Equine Disease Quarterly Newsletter

5
KENTUCKY

Equine Renal DiseaseRenal function is an important componentof overall health in any species. The kidneys
perform several important functions, including
waste removal, electrolyte balance, blood pressure
maintenance, a calcium source for bone health andproduction of factors for red blood cell stimulation, to name a few. In addition, the kidneys
receive substantial blood flow— approximately
25% of the cardiac output. Therefore, changes inblood flow, either increased or decreased, can havea significant impact on renal health.
Equine necropsy cases submitted to the University of Kentucky Veterinary Diagnostic Laboratory(UKVDL) over an eight-year period (2010-2018)
were queried for diagnoses related to renal pathology. Equine fetuses, foals, and adults of a variety
of breeds were included. It was determined that
3.6% (386/10,541) of equine submissions had
some type of renal pathology. Of those diagnoses,
renal lesions were determined to be primary in
38% of cases (n=148), secondary to another process in 55% of cases (n=211), or incidental in 7%
of cases (n=27).
Significant processes associated with primary lesions included: inflammatory/infectious (95 cases);congenital (21 cases); neoplastic renal carcinoma/
adenocarcinoma (10 cases); nephroliths (10 cases);
toxic (four cases); trauma (one case); and othermiscellaneous (i.e. chronic renal failure, protein
losing nephropathy) conditions (seven cases).
Within the infectious/inflammatory group,
the most common cause was a bacterial pathogen
resulting in nephritis. The largest proportion ofcases was due to Leptospira interrogans infections
in fetuses. Leptospirosis is a cause of abortion that
often localizes to the kidney. Actinobacillus equuli
was another common bacterial isolate, most often
seen in neonatal foals and occasionally adults.
In foals, infection with A. equuli is colloquiallytermed “sleepy foal disease.” Routes of infection
for A. equuli include a contaminated umbilicus,
inhalation or ingestion. Several cases of bacterial
pyelonephritis were identified. Pyelonephritis is
inflammation of the renal pelvis that most often
results from an infection that extends up to thekidneys from the lower urinary tract (i.e. urinary
bladder). The most common bacterial isolates
identified from cases at the UKVDL included

Streptococcus zooepidemicus, Escherichia coli, andEnterococcus sp.
Lesions that comprised the congenital category
included renal dysplasia, renal agenesis, congenital
renal cysts or congenital hydronephrosis/hydroureter. While there have been proposed associations of hereditary or nutritional components fordevelopmental renal abnormalities in some species(i.e. dogs and pigs), in horses the pathogenesis ofthese congenital lesions remains to be elucidated.
Significant nephroliths (kidney stones) wereidentified in 10 horses. The stones were composedof calcium carbonate or a mixture of calcium carbonate with other minerals. Typically, horses withnephroliths remain asymptomatic until the stone
results in obstruction. Development of nephroliths
has been associated with any nidus of renal disease
including cysts, papillary necrosis, pyelonephritis
or neoplasia.
Papillary (medullary crest) necrosis due tosuspected long-term use of non-steroidal antiinflammatory drugs (NSAIDs) was identified inthree of the four cases in the toxic category. NSAIDs(i.e. phenylbutazone/bute and flunixin meglumine/
Banamine) are routinely used in horses for pain
management. NSAIDs work by inhibiting a specificgroup of enzymes, cyclooxygenase (COX), which
subsequently reduces inflammation. Unfortunately,other downstream effects of this pathway include
decreased production of prostaglandins. Specificcells located in the renal medulla produce prostaglandins that are mediators of blood flow to the tissue. Therefore, decreased prostaglandin production
results in impaired blood flow to the medulla andsubsequent necrosis. Other compounding factors
include dehydration and use of multiple NSAIDs.
Luckily, renal complications due to NSAIDs arewell described with the result that there is judicious
use of these medications in practice.
The equine kidney has a vital role in overall
health. A variety of disease processes can impair
renal function. Awareness of these diseases is important for equine health.
CONTACT:
Jennifer Janes, DVM, PhD
jennifer.janes@uky.edu(859) 257-8283
University of Kentucky Veterinary Diagnostic Laboratory
Lexington, KY

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099

Presorted Standard
US Postage Paid
Permit 51
Lexington KY

Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

OCTOBER 2018
Volume 27, Number 4

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
Second Quarter2018  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2National
Asian Longhorned
Tick . . . . . . . . . . . . . . . . . 3
Muscular Disordersof Athletic Horses .  .  .  . 4KentuckyEquine Renal
Disease .  .  .  .  .  .  .  .  .  .  .  .  .  . 5

College of Agriculture,
Food and Environment
Department of
Veterinary ScienceVector or arthropod-borne diseases represent
some of the most significant threats to humanand animal health in certain regions/countries of
the world. An ever-increasing number have spreadbeyond historically defined boundaries, in no smallpart as a result of continued expansion in international trade of live animals or animal products andbecause of global climate change. The worldwide
spread of two human pathogens, Chikungunya
and Zika viruses, from the African continent inrecent years illustrates the major difficulties confronting the global community in containing theseand other arthropod-borne diseases.
Within the realm of infectious diseases, it ismore relevant in today’s world to consider populations of humans and animals in different countries
as co-existing in a global context, blurring theboundaries and reach of national political interests.
We have in essence become an international community in which social media play a major role incommunicating information across a spectrum ofissues, including disease events.
Aside from what is known of the diversity andrange of particular disease vectors in the USA, there
is a need to be mindful of the possible introductionof a particular arthropod, e.g. tick or mosquito,that has never been recorded previously in the
country—in other words, an invasive species.
The article in this issue of the Quarterly on the
discovery of the Asian longhorned tick (Haemaphysalis longicornis) for the first time in the USA
highlights the challenges that can be presented byan invasive tick species. Although shown to be acompetent vector of various diseases in a number
of Pacific Rim countries, the potential competencyof this particular tick to transmit animal or humandiseases in the country remains to be established.
Within recent months there have also been reports of the introduction of invasive species ofmosquito (Ochlerotatus japonicus) into Spain andof ticks (Hyalomma marginatum and H. rufipes)
into Germany.
Although the discovery of H. longicornis wasreported for the first time in 2018, subsequent
investigations have shown that the tick had beenin the USA at least since 2013. The lesson to belearned from this latest experience is that muchgreater surveillance and monitoring of tick andinsect populations in general is needed to establish
the range and distribution of the various species
with potential to serve as competent vectors ofknown mosquito and tick-borne diseases of equids.
To better prepare ourselves for dealing with
future disease threats, resources need to be madeavailable to support the infrastructure for morecomprehensive vector and disease surveillance
programs in conjunction with improved capacity
to respond to major disease events. The risk ofsuch threats will increase inevitably with continued
growth in the globalization of trade and the influence of climate change on our environment andthe spread of vectors and vector-borne diseases.
An integral element to better prepare ourselves
for the next disease threat is the need for greaterawareness and better education of practicing veterinarians who are frequently the “first responders” indealing with a case/outbreak of a novel disease ora possible invasive ecto-parasite. Increased public
education and engagement is also important inaddressing any disease threat that may evolve.
CONTACT:
Peter J. Timoney, MVB, MS, PhD, FRCVS
ptimoney@uky.edu(859) 218-1094
Charles Issel, DVM, PhD
cissel@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

2

3

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

I N T E R N AT I O N A L

N AT I O N A L

Second Quarter, 2018

Asian Longhorned Tick (Haemaphysalis longicornis):
Challenges from an Invasive Ixodid Tickhe International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following equine disease outbreaks.
The Republic of South Africa (RSA) reported
outbreaks of African horse sickness in most provinces in the country with the exception of theWestern Cape. One outbreak was recorded in
Swaziland.
Argentina, the UK, Uruguay, and the USA
reported outbreaks of equine influenza. At least 42
cases were confirmed on 10 premises located in fiveprovinces in Argentina. Three-year-old horses wereprincipally affected. The strain involved belonged
to clade 1, Florida sublineage of H3N8 virus. The
UK and Uruguay recorded single outbreaks of thedisease. Equine influenza was reported as endemic
in the USA, occurring in four states, with multiple
outbreaks in one state.
Germany, Ireland, Switzerland, the UK and
the USA recorded strangles. The number of outbreaks included six in Germany, outbreaks in all
four provinces in Ireland and eight in Switzerland.
The UK and the USA stated that the disease wasendemic in their respective countries. More than
85 outbreaks involving 178 cases were recorded in
24 states in the USA.
Equine herpesvirus 1 (EHV-1) infection wasreported by Belgium, Denmark, France, Germany,
Greece, Ireland, Japan, RSA, Switzerland, the UK,
and the USA. Infection associated with fever wasdiagnosed in three states in the USA. Respiratory
disease was confirmed in Belgium (10 outbreaks),
France (seven outbreaks), Germany (one case),
Switzerland (one outbreak), the UK (one outbreak)and the USA (widespread in various states). EHV1 abortion was recorded in Denmark (one case),
France (eight cases), Germany (12 cases), Japan(nine cases involving seven premises), RSA (twocases), the UK (five cases of which three were on
one premises), and the USA (two cases).
EHV-1 related disease in neonatal foals wasdiagnosed in France (one case) and the UK (twocases).
EHV-1 associated neurologic disease was reported from Denmark (two cases), France (fourcases), Germany (one case), Ireland (two cases),
and the USA (10 outbreaks in eight states; all but
one involved single cases of the disease).

Equine herpesvirus 4 (EHV-4) respiratory disease was recorded in Argentina (four outbreaks),
Belgium (one outbreak), France (59 outbreaks),
Germany, RSA and Switzerland (each confirmed
single cases of the disease), and the UK (fouroutbreaks). France and Germany reported single
cases of EHV-4 abortion.
The USA recorded multiple cases of equine herpesvirus 2 and/or 5 infection in several states, someassociated with a history of respiratory disease.
Equine infectious anemia was reported from
Canada (single cases on two premises), Germany(one case), Greece (one case), and the USA (18cases involving six states; 12 cases were in Texas).
RSA reported that equine piroplasmosis was
widely present in the country with multiple casesof the disease confirmed in five provinces.
Germany confirmed Taylorella equigenitalis, thecausal agent of contagious equine metritis in eightstallions and one mare, all of the Icelandic breed.
Seven premises were involved.
Single cases of equine coital exanthema caused
by equine herpesvirus 3 were recorded by Switzerland and the USA.
Cases of salmonellosis were reported from Ireland (one case) and the USA (12 cases, the majority
associated with strains of salmonella belonging toserogroup B). The USA confirmed three cases of
equine neorickettsiosis (Potomac horse fever), andGermany one case of rotaviral diarrhea in a foal.
A single case of rabies was confirmed in Nebraska, USA.
The USA recorded 10 cases of Eastern equine
encephalomyelitis, all in Florida.
Single cases of West Nile encephalitis werereported from Brazil and RSA.
RSA also recorded 16 cases of encephalitis due
to Middleburg virus infection and two cases due
to Shuni virus infection.
Equine encephalosis was reported from RSA.
Thirty-three cases were diagnosed in five provinces;these included seven in the Western Cape Province.
Rhodococcus equi infection is endemic in theUSA; 14 cases were confirmed during the period
under review.
Germany reported a case of anaplasmosis andSwitzerland four cases of ehrlichiosis.

Asian longhorned ticks (ALT) have small,
reddish-brown bodies with no distinctive
markings to facilitate quick recognition. In addition, unfed adults are smaller (3 to 4 mm long)than the familiar commonly encountered hardticks. The initial confirmed identification of ALT
in the USA was based on specimens collectedfrom a heavily-infested sheep in New Jersey in2017. This was thought to be the first detectionof a new tick species in the USA in 50 years.
However, subsequent investigation revealed thatspecimens removed from a dog in New Jersey in2013, which were initially identified as the native
rabbit tick Haemaphysalis leporispalustris, were also
ALT. Consequently, the species has been present
for several years and has spread. As of August 2018,
this invasive tick has been found in at least one
location in Arkansas, Connecticut, Maryland, New
Jersey, New York, North Carolina, Pennsylvania,
Virginia, and West Virginia (Figure 1). Reported
hosts have included cattle, a dog, a horse, an opossum, and white-tailed deer.
Native to China, Korea, and Japan, the ALT
became established in Australia and New Zealand,
where it feeds on a variety of wild and domestic
animals and humans. This species does best in
moist, warm environments. However, it canwithstand temperatures from its developmental
threshold of ~12ºC to a lethal high temperature of
40ºC. Adults and particularly larval stages of thespecies appear to have a relatively low tolerance of
dehydration, which may play an important role inits ultimate distribution in the USA.
The ALT is a three-host tick with a life cyclethat takes about a year. While males and females
occur in approximately equal numbers over its

native habitat, very few males have been foundin the USA. Apparently, parthenogenesis (female
reproduction without the need of fertilization bya male) is a significant feature of its biology in the
USA (Figure 2). Females can deposit about 2,000
eggs, all females, so local populations can growrapidly following establishment. This can result insignificant blood loss and stress to infested hosts.
While the initial introduction(s) of this tick is
unknown, genetic mapping has identified threemitochondrial DNA lineages. This points to atleast three distinct females lineages. Parthenogenesis would allow relatively rapid selection forbiotypes in response to environmental factors in
its new habitat.
Collections of ALT from sheep in China indicate the ears and periocular areas are preferredattachment sites. Specimens collected and tested in
the USA have not been shown to carry any diseases,
but ALT are competent disease vectors in Asia
contributing to theileriosis and babesiosis in cattlein Australia and New Zealand and anaplasmosis
in Korea. Severe fever with thrombocytopenia
syndrome (SFTS) is an emerging hemorrhagic
fever in East Asia caused by SFTS virus (SFTSV),a newly discovered phlebovirus. The Haemaphysalis
longicornis tick has been suspected to be the vector of SFTSV. Time will tell the story of its vector
potential in North America. Preserved specimensof suspected Asian longhorned ticks should be sent
to the National Veterinary Services Laboratories inAmes, Iowa for identification.
CONTACT:
Lee Townsend, MS, PhD
ltownsen@uky.edu(859) 257-7455
Department of Entomology
University of Kentucky
Lexington, KY

Muscular Disorders of Athletic Horses

4

T

Figure 1. Known
U.S. distribution of
Haemaphysalis longicornis(as of August 30, 2018).

Figure 2. The female Asian longhorned tick (ALT) (Haemaphysalis
longicornis) is able to reproduce without male fertilization to rapidly growlocal populations after establishment. ALT are able to deposit about 2,000
eggs, all female. Male ALT in the United States are rare. Source: James
Gathany, Centers for Disease Control and Prevention

he equine muscular system is the engine roomof the horse, comprising over half of the bodymass of Thoroughbreds. At the cellular level it is acomplex system, comprised of a vast array of specialized proteins that coordinate functions ranging
from power output to heat management. Disordersof the muscular system cause poor performanceand in some cases, death; yet in certain groups ofathletic horses, 5% to 25% of individuals haveheritable muscular disorders. Muscle disorders
are very common in athletic horse breeds because,
surprisingly, they can also provide some beneficial
effects, ranging from enhanced muscle mass toeconomic metabolism.
Given the importance of the muscular system
to athletic performance of the horse, not surprisingly, it has attracted considerable research focus.
In the past two decades, “tying-up” up in athletic
horses has been teased into at least three distinct
disorders, which are heritable and therefore tend
to have strong breed predispositions. Several otherheritable muscular disorders of horses have also
been defined, causing problems ranging fromprofound weakness to respiratory paralysis andearly neonatal death. Advances in medicine now
permit convenient hair or blood tests for manyof these diseases due to their genetic basis, andbreeders are encouraged to display appropriate
stewardship by testing their breeding stock for
known disorders that have scientifically validated
genetic tests available. Current research efforts
are attempting to identify the genetic signatureof the disease causing tying-up in Thoroughbreds
and Standardbreds, which has proved challenging,and the disease causing tying-up in Arabian horses.
Advanced molecular techniques are also being applied to some disorders to determine exactly whatgoes wrong at the cellular level, to help define
the basis of clinical signs and to better direct thedevelopment of effective genetic tests.
Currently, the most clearly defined musculardisorders of athletic breeds are polysaccharide
storage myopathy (PSSM), hyperkalemic periodic
paralysis (HYPP), and glycogen branching enzyme
deficiency (GBED), because the cellular nature ofthese diseases and the underlying causative genetic
mutations are largely defined. PSSM is common
in Quarter horses and related breeds, and typicallycauses signs of tying-up. It is also linked to highbody condition, which can be desirable in those
breeds. HYPP causes weakness and paralysis and,occasionally, death. It is also associated with highmuscle mass, and therefore became prevalent due
to positive selection pressure for this trait. GBED
is an inevitably fatal disorder of Quarter Horses
and Paints, causing weakness and death in thefirst days to weeks of life. It is uncommon, andassociation with a positive trait is not recognized.
All three of these disorders can be readily tested
for on hair or blood.
Standardbred and Thoroughbred horses appear
to share a disorder causing tying-up during training, with clinical signs rarely or never seen during
actual racing exercise. This disease is referred to asrecurrent exertional rhabdomyolysis (RER). It appears to be more common in faster horses because
it might permit more rapid muscular processes atthe cellular level, hence there has been positive
selection pressure on this disease. The geneticsof RER have proven frustrating to define despite
many years of work. Warmblood and Arabianhorses might also share a disorder recently coined
as “myofibrillar myopathy” (MFM). Signs of thisdisease appear to consist of tying-up in Arabianhorses, and poor performance and poorly defined
movement abnormalities in Warmblood horses.
The genetic cause of MFM is not known and no
scientifically validated genetic tests exist for MFM
or RER.
In summary, muscular disorders are common
in athletic horses, and can be frustrating andeven fatal under some circumstances. Association
with specific positive traits has contributed to theprevalence of some of these diseases. Genetic testing is available for many heritable equine diseases,
and it is likely that testing for less clearly defineddisorders will be developed in the coming years.
Genetic stewardship relies on breeders being educated about heritable disorders, and performing
proactive breeding selection processes to produce
horses that are not only high performers but also
genetically sound.
CONTACT:
Erica McKenzie, BSc, BVMS, PhD, DACVIM, DACVSMR
erica.mckenzie@oregonstate.edu(541) 737-2858
Carlson College of Veterinary Medicine
Oregon State University
Corvallis, OR

2

3

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

I N T E R N AT I O N A L

N AT I O N A L

Second Quarter, 2018

Asian Longhorned Tick (Haemaphysalis longicornis):
Challenges from an Invasive Ixodid Tickhe International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following equine disease outbreaks.
The Republic of South Africa (RSA) reported
outbreaks of African horse sickness in most provinces in the country with the exception of theWestern Cape. One outbreak was recorded in
Swaziland.
Argentina, the UK, Uruguay, and the USA
reported outbreaks of equine influenza. At least 42
cases were confirmed on 10 premises located in fiveprovinces in Argentina. Three-year-old horses wereprincipally affected. The strain involved belonged
to clade 1, Florida sublineage of H3N8 virus. The
UK and Uruguay recorded single outbreaks of thedisease. Equine influenza was reported as endemic
in the USA, occurring in four states, with multiple
outbreaks in one state.
Germany, Ireland, Switzerland, the UK and
the USA recorded strangles. The number of outbreaks included six in Germany, outbreaks in all
four provinces in Ireland and eight in Switzerland.
The UK and the USA stated that the disease wasendemic in their respective countries. More than
85 outbreaks involving 178 cases were recorded in
24 states in the USA.
Equine herpesvirus 1 (EHV-1) infection wasreported by Belgium, Denmark, France, Germany,
Greece, Ireland, Japan, RSA, Switzerland, the UK,
and the USA. Infection associated with fever wasdiagnosed in three states in the USA. Respiratory
disease was confirmed in Belgium (10 outbreaks),
France (seven outbreaks), Germany (one case),
Switzerland (one outbreak), the UK (one outbreak)and the USA (widespread in various states). EHV1 abortion was recorded in Denmark (one case),
France (eight cases), Germany (12 cases), Japan(nine cases involving seven premises), RSA (twocases), the UK (five cases of which three were on
one premises), and the USA (two cases).
EHV-1 related disease in neonatal foals wasdiagnosed in France (one case) and the UK (twocases).
EHV-1 associated neurologic disease was reported from Denmark (two cases), France (fourcases), Germany (one case), Ireland (two cases),
and the USA (10 outbreaks in eight states; all but
one involved single cases of the disease).

Equine herpesvirus 4 (EHV-4) respiratory disease was recorded in Argentina (four outbreaks),
Belgium (one outbreak), France (59 outbreaks),
Germany, RSA and Switzerland (each confirmed
single cases of the disease), and the UK (fouroutbreaks). France and Germany reported single
cases of EHV-4 abortion.
The USA recorded multiple cases of equine herpesvirus 2 and/or 5 infection in several states, someassociated with a history of respiratory disease.
Equine infectious anemia was reported from
Canada (single cases on two premises), Germany(one case), Greece (one case), and the USA (18cases involving six states; 12 cases were in Texas).
RSA reported that equine piroplasmosis was
widely present in the country with multiple casesof the disease confirmed in five provinces.
Germany confirmed Taylorella equigenitalis, thecausal agent of contagious equine metritis in eightstallions and one mare, all of the Icelandic breed.
Seven premises were involved.
Single cases of equine coital exanthema caused
by equine herpesvirus 3 were recorded by Switzerland and the USA.
Cases of salmonellosis were reported from Ireland (one case) and the USA (12 cases, the majority
associated with strains of salmonella belonging toserogroup B). The USA confirmed three cases of
equine neorickettsiosis (Potomac horse fever), andGermany one case of rotaviral diarrhea in a foal.
A single case of rabies was confirmed in Nebraska, USA.
The USA recorded 10 cases of Eastern equine
encephalomyelitis, all in Florida.
Single cases of West Nile encephalitis werereported from Brazil and RSA.
RSA also recorded 16 cases of encephalitis due
to Middleburg virus infection and two cases due
to Shuni virus infection.
Equine encephalosis was reported from RSA.
Thirty-three cases were diagnosed in five provinces;these included seven in the Western Cape Province.
Rhodococcus equi infection is endemic in theUSA; 14 cases were confirmed during the period
under review.
Germany reported a case of anaplasmosis andSwitzerland four cases of ehrlichiosis.

Asian longhorned ticks (ALT) have small,
reddish-brown bodies with no distinctive
markings to facilitate quick recognition. In addition, unfed adults are smaller (3 to 4 mm long)than the familiar commonly encountered hardticks. The initial confirmed identification of ALT
in the USA was based on specimens collectedfrom a heavily-infested sheep in New Jersey in2017. This was thought to be the first detectionof a new tick species in the USA in 50 years.
However, subsequent investigation revealed thatspecimens removed from a dog in New Jersey in2013, which were initially identified as the native
rabbit tick Haemaphysalis leporispalustris, were also
ALT. Consequently, the species has been present
for several years and has spread. As of August 2018,
this invasive tick has been found in at least one
location in Arkansas, Connecticut, Maryland, New
Jersey, New York, North Carolina, Pennsylvania,
Virginia, and West Virginia (Figure 1). Reported
hosts have included cattle, a dog, a horse, an opossum, and white-tailed deer.
Native to China, Korea, and Japan, the ALT
became established in Australia and New Zealand,
where it feeds on a variety of wild and domestic
animals and humans. This species does best in
moist, warm environments. However, it canwithstand temperatures from its developmental
threshold of ~12ºC to a lethal high temperature of
40ºC. Adults and particularly larval stages of thespecies appear to have a relatively low tolerance of
dehydration, which may play an important role inits ultimate distribution in the USA.
The ALT is a three-host tick with a life cyclethat takes about a year. While males and females
occur in approximately equal numbers over its

native habitat, very few males have been foundin the USA. Apparently, parthenogenesis (female
reproduction without the need of fertilization bya male) is a significant feature of its biology in the
USA (Figure 2). Females can deposit about 2,000
eggs, all females, so local populations can growrapidly following establishment. This can result insignificant blood loss and stress to infested hosts.
While the initial introduction(s) of this tick is
unknown, genetic mapping has identified threemitochondrial DNA lineages. This points to atleast three distinct females lineages. Parthenogenesis would allow relatively rapid selection forbiotypes in response to environmental factors in
its new habitat.
Collections of ALT from sheep in China indicate the ears and periocular areas are preferredattachment sites. Specimens collected and tested in
the USA have not been shown to carry any diseases,
but ALT are competent disease vectors in Asia
contributing to theileriosis and babesiosis in cattlein Australia and New Zealand and anaplasmosis
in Korea. Severe fever with thrombocytopenia
syndrome (SFTS) is an emerging hemorrhagic
fever in East Asia caused by SFTS virus (SFTSV),a newly discovered phlebovirus. The Haemaphysalis
longicornis tick has been suspected to be the vector of SFTSV. Time will tell the story of its vector
potential in North America. Preserved specimensof suspected Asian longhorned ticks should be sent
to the National Veterinary Services Laboratories inAmes, Iowa for identification.
CONTACT:
Lee Townsend, MS, PhD
ltownsen@uky.edu(859) 257-7455
Department of Entomology
University of Kentucky
Lexington, KY

Muscular Disorders of Athletic Horses

4

T

Figure 1. Known
U.S. distribution of
Haemaphysalis longicornis(as of August 30, 2018).

Figure 2. The female Asian longhorned tick (ALT) (Haemaphysalis
longicornis) is able to reproduce without male fertilization to rapidly growlocal populations after establishment. ALT are able to deposit about 2,000
eggs, all female. Male ALT in the United States are rare. Source: James
Gathany, Centers for Disease Control and Prevention

he equine muscular system is the engine roomof the horse, comprising over half of the bodymass of Thoroughbreds. At the cellular level it is acomplex system, comprised of a vast array of specialized proteins that coordinate functions ranging
from power output to heat management. Disordersof the muscular system cause poor performanceand in some cases, death; yet in certain groups ofathletic horses, 5% to 25% of individuals haveheritable muscular disorders. Muscle disorders
are very common in athletic horse breeds because,
surprisingly, they can also provide some beneficial
effects, ranging from enhanced muscle mass toeconomic metabolism.
Given the importance of the muscular system
to athletic performance of the horse, not surprisingly, it has attracted considerable research focus.
In the past two decades, “tying-up” up in athletic
horses has been teased into at least three distinct
disorders, which are heritable and therefore tend
to have strong breed predispositions. Several otherheritable muscular disorders of horses have also
been defined, causing problems ranging fromprofound weakness to respiratory paralysis andearly neonatal death. Advances in medicine now
permit convenient hair or blood tests for manyof these diseases due to their genetic basis, andbreeders are encouraged to display appropriate
stewardship by testing their breeding stock for
known disorders that have scientifically validated
genetic tests available. Current research efforts
are attempting to identify the genetic signatureof the disease causing tying-up in Thoroughbreds
and Standardbreds, which has proved challenging,and the disease causing tying-up in Arabian horses.
Advanced molecular techniques are also being applied to some disorders to determine exactly whatgoes wrong at the cellular level, to help define
the basis of clinical signs and to better direct thedevelopment of effective genetic tests.
Currently, the most clearly defined musculardisorders of athletic breeds are polysaccharide
storage myopathy (PSSM), hyperkalemic periodic
paralysis (HYPP), and glycogen branching enzyme
deficiency (GBED), because the cellular nature ofthese diseases and the underlying causative genetic
mutations are largely defined. PSSM is common
in Quarter horses and related breeds, and typicallycauses signs of tying-up. It is also linked to highbody condition, which can be desirable in those
breeds. HYPP causes weakness and paralysis and,occasionally, death. It is also associated with highmuscle mass, and therefore became prevalent due
to positive selection pressure for this trait. GBED
is an inevitably fatal disorder of Quarter Horses
and Paints, causing weakness and death in thefirst days to weeks of life. It is uncommon, andassociation with a positive trait is not recognized.
All three of these disorders can be readily tested
for on hair or blood.
Standardbred and Thoroughbred horses appear
to share a disorder causing tying-up during training, with clinical signs rarely or never seen during
actual racing exercise. This disease is referred to asrecurrent exertional rhabdomyolysis (RER). It appears to be more common in faster horses because
it might permit more rapid muscular processes atthe cellular level, hence there has been positive
selection pressure on this disease. The geneticsof RER have proven frustrating to define despite
many years of work. Warmblood and Arabianhorses might also share a disorder recently coined
as “myofibrillar myopathy” (MFM). Signs of thisdisease appear to consist of tying-up in Arabianhorses, and poor performance and poorly defined
movement abnormalities in Warmblood horses.
The genetic cause of MFM is not known and no
scientifically validated genetic tests exist for MFM
or RER.
In summary, muscular disorders are common
in athletic horses, and can be frustrating andeven fatal under some circumstances. Association
with specific positive traits has contributed to theprevalence of some of these diseases. Genetic testing is available for many heritable equine diseases,
and it is likely that testing for less clearly defineddisorders will be developed in the coming years.
Genetic stewardship relies on breeders being educated about heritable disorders, and performing
proactive breeding selection processes to produce
horses that are not only high performers but also
genetically sound.
CONTACT:
Erica McKenzie, BSc, BVMS, PhD, DACVIM, DACVSMR
erica.mckenzie@oregonstate.edu(541) 737-2858
Carlson College of Veterinary Medicine
Oregon State University
Corvallis, OR

2

3

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

I N T E R N AT I O N A L

N AT I O N A L

Second Quarter, 2018

Asian Longhorned Tick (Haemaphysalis longicornis):
Challenges from an Invasive Ixodid Tickhe International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following equine disease outbreaks.
The Republic of South Africa (RSA) reported
outbreaks of African horse sickness in most provinces in the country with the exception of theWestern Cape. One outbreak was recorded in
Swaziland.
Argentina, the UK, Uruguay, and the USA
reported outbreaks of equine influenza. At least 42
cases were confirmed on 10 premises located in fiveprovinces in Argentina. Three-year-old horses wereprincipally affected. The strain involved belonged
to clade 1, Florida sublineage of H3N8 virus. The
UK and Uruguay recorded single outbreaks of thedisease. Equine influenza was reported as endemic
in the USA, occurring in four states, with multiple
outbreaks in one state.
Germany, Ireland, Switzerland, the UK and
the USA recorded strangles. The number of outbreaks included six in Germany, outbreaks in all
four provinces in Ireland and eight in Switzerland.
The UK and the USA stated that the disease wasendemic in their respective countries. More than
85 outbreaks involving 178 cases were recorded in
24 states in the USA.
Equine herpesvirus 1 (EHV-1) infection wasreported by Belgium, Denmark, France, Germany,
Greece, Ireland, Japan, RSA, Switzerland, the UK,
and the USA. Infection associated with fever wasdiagnosed in three states in the USA. Respiratory
disease was confirmed in Belgium (10 outbreaks),
France (seven outbreaks), Germany (one case),
Switzerland (one outbreak), the UK (one outbreak)and the USA (widespread in various states). EHV1 abortion was recorded in Denmark (one case),
France (eight cases), Germany (12 cases), Japan(nine cases involving seven premises), RSA (twocases), the UK (five cases of which three were on
one premises), and the USA (two cases).
EHV-1 related disease in neonatal foals wasdiagnosed in France (one case) and the UK (twocases).
EHV-1 associated neurologic disease was reported from Denmark (two cases), France (fourcases), Germany (one case), Ireland (two cases),
and the USA (10 outbreaks in eight states; all but
one involved single cases of the disease).

Equine herpesvirus 4 (EHV-4) respiratory disease was recorded in Argentina (four outbreaks),
Belgium (one outbreak), France (59 outbreaks),
Germany, RSA and Switzerland (each confirmed
single cases of the disease), and the UK (fouroutbreaks). France and Germany reported single
cases of EHV-4 abortion.
The USA recorded multiple cases of equine herpesvirus 2 and/or 5 infection in several states, someassociated with a history of respiratory disease.
Equine infectious anemia was reported from
Canada (single cases on two premises), Germany(one case), Greece (one case), and the USA (18cases involving six states; 12 cases were in Texas).
RSA reported that equine piroplasmosis was
widely present in the country with multiple casesof the disease confirmed in five provinces.
Germany confirmed Taylorella equigenitalis, thecausal agent of contagious equine metritis in eightstallions and one mare, all of the Icelandic breed.
Seven premises were involved.
Single cases of equine coital exanthema caused
by equine herpesvirus 3 were recorded by Switzerland and the USA.
Cases of salmonellosis were reported from Ireland (one case) and the USA (12 cases, the majority
associated with strains of salmonella belonging toserogroup B). The USA confirmed three cases of
equine neorickettsiosis (Potomac horse fever), andGermany one case of rotaviral diarrhea in a foal.
A single case of rabies was confirmed in Nebraska, USA.
The USA recorded 10 cases of Eastern equine
encephalomyelitis, all in Florida.
Single cases of West Nile encephalitis werereported from Brazil and RSA.
RSA also recorded 16 cases of encephalitis due
to Middleburg virus infection and two cases due
to Shuni virus infection.
Equine encephalosis was reported from RSA.
Thirty-three cases were diagnosed in five provinces;these included seven in the Western Cape Province.
Rhodococcus equi infection is endemic in theUSA; 14 cases were confirmed during the period
under review.
Germany reported a case of anaplasmosis andSwitzerland four cases of ehrlichiosis.

Asian longhorned ticks (ALT) have small,
reddish-brown bodies with no distinctive
markings to facilitate quick recognition. In addition, unfed adults are smaller (3 to 4 mm long)than the familiar commonly encountered hardticks. The initial confirmed identification of ALT
in the USA was based on specimens collectedfrom a heavily-infested sheep in New Jersey in2017. This was thought to be the first detectionof a new tick species in the USA in 50 years.
However, subsequent investigation revealed thatspecimens removed from a dog in New Jersey in2013, which were initially identified as the native
rabbit tick Haemaphysalis leporispalustris, were also
ALT. Consequently, the species has been present
for several years and has spread. As of August 2018,
this invasive tick has been found in at least one
location in Arkansas, Connecticut, Maryland, New
Jersey, New York, North Carolina, Pennsylvania,
Virginia, and West Virginia (Figure 1). Reported
hosts have included cattle, a dog, a horse, an opossum, and white-tailed deer.
Native to China, Korea, and Japan, the ALT
became established in Australia and New Zealand,
where it feeds on a variety of wild and domestic
animals and humans. This species does best in
moist, warm environments. However, it canwithstand temperatures from its developmental
threshold of ~12ºC to a lethal high temperature of
40ºC. Adults and particularly larval stages of thespecies appear to have a relatively low tolerance of
dehydration, which may play an important role inits ultimate distribution in the USA.
The ALT is a three-host tick with a life cyclethat takes about a year. While males and females
occur in approximately equal numbers over its

native habitat, very few males have been foundin the USA. Apparently, parthenogenesis (female
reproduction without the need of fertilization bya male) is a significant feature of its biology in the
USA (Figure 2). Females can deposit about 2,000
eggs, all females, so local populations can growrapidly following establishment. This can result insignificant blood loss and stress to infested hosts.
While the initial introduction(s) of this tick is
unknown, genetic mapping has identified threemitochondrial DNA lineages. This points to atleast three distinct females lineages. Parthenogenesis would allow relatively rapid selection forbiotypes in response to environmental factors in
its new habitat.
Collections of ALT from sheep in China indicate the ears and periocular areas are preferredattachment sites. Specimens collected and tested in
the USA have not been shown to carry any diseases,
but ALT are competent disease vectors in Asia
contributing to theileriosis and babesiosis in cattlein Australia and New Zealand and anaplasmosis
in Korea. Severe fever with thrombocytopenia
syndrome (SFTS) is an emerging hemorrhagic
fever in East Asia caused by SFTS virus (SFTSV),a newly discovered phlebovirus. The Haemaphysalis
longicornis tick has been suspected to be the vector of SFTSV. Time will tell the story of its vector
potential in North America. Preserved specimensof suspected Asian longhorned ticks should be sent
to the National Veterinary Services Laboratories inAmes, Iowa for identification.
CONTACT:
Lee Townsend, MS, PhD
ltownsen@uky.edu(859) 257-7455
Department of Entomology
University of Kentucky
Lexington, KY

Muscular Disorders of Athletic Horses

4

T

Figure 1. Known
U.S. distribution of
Haemaphysalis longicornis(as of August 30, 2018).

Figure 2. The female Asian longhorned tick (ALT) (Haemaphysalis
longicornis) is able to reproduce without male fertilization to rapidly growlocal populations after establishment. ALT are able to deposit about 2,000
eggs, all female. Male ALT in the United States are rare. Source: James
Gathany, Centers for Disease Control and Prevention

he equine muscular system is the engine roomof the horse, comprising over half of the bodymass of Thoroughbreds. At the cellular level it is acomplex system, comprised of a vast array of specialized proteins that coordinate functions ranging
from power output to heat management. Disordersof the muscular system cause poor performanceand in some cases, death; yet in certain groups ofathletic horses, 5% to 25% of individuals haveheritable muscular disorders. Muscle disorders
are very common in athletic horse breeds because,
surprisingly, they can also provide some beneficial
effects, ranging from enhanced muscle mass toeconomic metabolism.
Given the importance of the muscular system
to athletic performance of the horse, not surprisingly, it has attracted considerable research focus.
In the past two decades, “tying-up” up in athletic
horses has been teased into at least three distinct
disorders, which are heritable and therefore tend
to have strong breed predispositions. Several otherheritable muscular disorders of horses have also
been defined, causing problems ranging fromprofound weakness to respiratory paralysis andearly neonatal death. Advances in medicine now
permit convenient hair or blood tests for manyof these diseases due to their genetic basis, andbreeders are encouraged to display appropriate
stewardship by testing their breeding stock for
known disorders that have scientifically validated
genetic tests available. Current research efforts
are attempting to identify the genetic signatureof the disease causing tying-up in Thoroughbreds
and Standardbreds, which has proved challenging,and the disease causing tying-up in Arabian horses.
Advanced molecular techniques are also being applied to some disorders to determine exactly whatgoes wrong at the cellular level, to help define
the basis of clinical signs and to better direct thedevelopment of effective genetic tests.
Currently, the most clearly defined musculardisorders of athletic breeds are polysaccharide
storage myopathy (PSSM), hyperkalemic periodic
paralysis (HYPP), and glycogen branching enzyme
deficiency (GBED), because the cellular nature ofthese diseases and the underlying causative genetic
mutations are largely defined. PSSM is common
in Quarter horses and related breeds, and typicallycauses signs of tying-up. It is also linked to highbody condition, which can be desirable in those
breeds. HYPP causes weakness and paralysis and,occasionally, death. It is also associated with highmuscle mass, and therefore became prevalent due
to positive selection pressure for this trait. GBED
is an inevitably fatal disorder of Quarter Horses
and Paints, causing weakness and death in thefirst days to weeks of life. It is uncommon, andassociation with a positive trait is not recognized.
All three of these disorders can be readily tested
for on hair or blood.
Standardbred and Thoroughbred horses appear
to share a disorder causing tying-up during training, with clinical signs rarely or never seen during
actual racing exercise. This disease is referred to asrecurrent exertional rhabdomyolysis (RER). It appears to be more common in faster horses because
it might permit more rapid muscular processes atthe cellular level, hence there has been positive
selection pressure on this disease. The geneticsof RER have proven frustrating to define despite
many years of work. Warmblood and Arabianhorses might also share a disorder recently coined
as “myofibrillar myopathy” (MFM). Signs of thisdisease appear to consist of tying-up in Arabianhorses, and poor performance and poorly defined
movement abnormalities in Warmblood horses.
The genetic cause of MFM is not known and no
scientifically validated genetic tests exist for MFM
or RER.
In summary, muscular disorders are common
in athletic horses, and can be frustrating andeven fatal under some circumstances. Association
with specific positive traits has contributed to theprevalence of some of these diseases. Genetic testing is available for many heritable equine diseases,
and it is likely that testing for less clearly defineddisorders will be developed in the coming years.
Genetic stewardship relies on breeders being educated about heritable disorders, and performing
proactive breeding selection processes to produce
horses that are not only high performers but also
genetically sound.
CONTACT:
Erica McKenzie, BSc, BVMS, PhD, DACVIM, DACVSMR
erica.mckenzie@oregonstate.edu(541) 737-2858
Carlson College of Veterinary Medicine
Oregon State University
Corvallis, OR

2

3

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

I N T E R N AT I O N A L

N AT I O N A L

Second Quarter, 2018

Asian Longhorned Tick (Haemaphysalis longicornis):
Challenges from an Invasive Ixodid Tickhe International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following equine disease outbreaks.
The Republic of South Africa (RSA) reported
outbreaks of African horse sickness in most provinces in the country with the exception of theWestern Cape. One outbreak was recorded in
Swaziland.
Argentina, the UK, Uruguay, and the USA
reported outbreaks of equine influenza. At least 42
cases were confirmed on 10 premises located in fiveprovinces in Argentina. Three-year-old horses wereprincipally affected. The strain involved belonged
to clade 1, Florida sublineage of H3N8 virus. The
UK and Uruguay recorded single outbreaks of thedisease. Equine influenza was reported as endemic
in the USA, occurring in four states, with multiple
outbreaks in one state.
Germany, Ireland, Switzerland, the UK and
the USA recorded strangles. The number of outbreaks included six in Germany, outbreaks in all
four provinces in Ireland and eight in Switzerland.
The UK and the USA stated that the disease wasendemic in their respective countries. More than
85 outbreaks involving 178 cases were recorded in
24 states in the USA.
Equine herpesvirus 1 (EHV-1) infection wasreported by Belgium, Denmark, France, Germany,
Greece, Ireland, Japan, RSA, Switzerland, the UK,
and the USA. Infection associated with fever wasdiagnosed in three states in the USA. Respiratory
disease was confirmed in Belgium (10 outbreaks),
France (seven outbreaks), Germany (one case),
Switzerland (one outbreak), the UK (one outbreak)and the USA (widespread in various states). EHV1 abortion was recorded in Denmark (one case),
France (eight cases), Germany (12 cases), Japan(nine cases involving seven premises), RSA (twocases), the UK (five cases of which three were on
one premises), and the USA (two cases).
EHV-1 related disease in neonatal foals wasdiagnosed in France (one case) and the UK (twocases).
EHV-1 associated neurologic disease was reported from Denmark (two cases), France (fourcases), Germany (one case), Ireland (two cases),
and the USA (10 outbreaks in eight states; all but
one involved single cases of the disease).

Equine herpesvirus 4 (EHV-4) respiratory disease was recorded in Argentina (four outbreaks),
Belgium (one outbreak), France (59 outbreaks),
Germany, RSA and Switzerland (each confirmed
single cases of the disease), and the UK (fouroutbreaks). France and Germany reported single
cases of EHV-4 abortion.
The USA recorded multiple cases of equine herpesvirus 2 and/or 5 infection in several states, someassociated with a history of respiratory disease.
Equine infectious anemia was reported from
Canada (single cases on two premises), Germany(one case), Greece (one case), and the USA (18cases involving six states; 12 cases were in Texas).
RSA reported that equine piroplasmosis was
widely present in the country with multiple casesof the disease confirmed in five provinces.
Germany confirmed Taylorella equigenitalis, thecausal agent of contagious equine metritis in eightstallions and one mare, all of the Icelandic breed.
Seven premises were involved.
Single cases of equine coital exanthema caused
by equine herpesvirus 3 were recorded by Switzerland and the USA.
Cases of salmonellosis were reported from Ireland (one case) and the USA (12 cases, the majority
associated with strains of salmonella belonging toserogroup B). The USA confirmed three cases of
equine neorickettsiosis (Potomac horse fever), andGermany one case of rotaviral diarrhea in a foal.
A single case of rabies was confirmed in Nebraska, USA.
The USA recorded 10 cases of Eastern equine
encephalomyelitis, all in Florida.
Single cases of West Nile encephalitis werereported from Brazil and RSA.
RSA also recorded 16 cases of encephalitis due
to Middleburg virus infection and two cases due
to Shuni virus infection.
Equine encephalosis was reported from RSA.
Thirty-three cases were diagnosed in five provinces;these included seven in the Western Cape Province.
Rhodococcus equi infection is endemic in theUSA; 14 cases were confirmed during the period
under review.
Germany reported a case of anaplasmosis andSwitzerland four cases of ehrlichiosis.

Asian longhorned ticks (ALT) have small,
reddish-brown bodies with no distinctive
markings to facilitate quick recognition. In addition, unfed adults are smaller (3 to 4 mm long)than the familiar commonly encountered hardticks. The initial confirmed identification of ALT
in the USA was based on specimens collectedfrom a heavily-infested sheep in New Jersey in2017. This was thought to be the first detectionof a new tick species in the USA in 50 years.
However, subsequent investigation revealed thatspecimens removed from a dog in New Jersey in2013, which were initially identified as the native
rabbit tick Haemaphysalis leporispalustris, were also
ALT. Consequently, the species has been present
for several years and has spread. As of August 2018,
this invasive tick has been found in at least one
location in Arkansas, Connecticut, Maryland, New
Jersey, New York, North Carolina, Pennsylvania,
Virginia, and West Virginia (Figure 1). Reported
hosts have included cattle, a dog, a horse, an opossum, and white-tailed deer.
Native to China, Korea, and Japan, the ALT
became established in Australia and New Zealand,
where it feeds on a variety of wild and domestic
animals and humans. This species does best in
moist, warm environments. However, it canwithstand temperatures from its developmental
threshold of ~12ºC to a lethal high temperature of
40ºC. Adults and particularly larval stages of thespecies appear to have a relatively low tolerance of
dehydration, which may play an important role inits ultimate distribution in the USA.
The ALT is a three-host tick with a life cyclethat takes about a year. While males and females
occur in approximately equal numbers over its

native habitat, very few males have been foundin the USA. Apparently, parthenogenesis (female
reproduction without the need of fertilization bya male) is a significant feature of its biology in the
USA (Figure 2). Females can deposit about 2,000
eggs, all females, so local populations can growrapidly following establishment. This can result insignificant blood loss and stress to infested hosts.
While the initial introduction(s) of this tick is
unknown, genetic mapping has identified threemitochondrial DNA lineages. This points to atleast three distinct females lineages. Parthenogenesis would allow relatively rapid selection forbiotypes in response to environmental factors in
its new habitat.
Collections of ALT from sheep in China indicate the ears and periocular areas are preferredattachment sites. Specimens collected and tested in
the USA have not been shown to carry any diseases,
but ALT are competent disease vectors in Asia
contributing to theileriosis and babesiosis in cattlein Australia and New Zealand and anaplasmosis
in Korea. Severe fever with thrombocytopenia
syndrome (SFTS) is an emerging hemorrhagic
fever in East Asia caused by SFTS virus (SFTSV),a newly discovered phlebovirus. The Haemaphysalis
longicornis tick has been suspected to be the vector of SFTSV. Time will tell the story of its vector
potential in North America. Preserved specimensof suspected Asian longhorned ticks should be sent
to the National Veterinary Services Laboratories inAmes, Iowa for identification.
CONTACT:
Lee Townsend, MS, PhD
ltownsen@uky.edu(859) 257-7455
Department of Entomology
University of Kentucky
Lexington, KY

Muscular Disorders of Athletic Horses

4

T

Figure 1. Known
U.S. distribution of
Haemaphysalis longicornis(as of August 30, 2018).

Figure 2. The female Asian longhorned tick (ALT) (Haemaphysalis
longicornis) is able to reproduce without male fertilization to rapidly growlocal populations after establishment. ALT are able to deposit about 2,000
eggs, all female. Male ALT in the United States are rare. Source: James
Gathany, Centers for Disease Control and Prevention

he equine muscular system is the engine roomof the horse, comprising over half of the bodymass of Thoroughbreds. At the cellular level it is acomplex system, comprised of a vast array of specialized proteins that coordinate functions ranging
from power output to heat management. Disordersof the muscular system cause poor performanceand in some cases, death; yet in certain groups ofathletic horses, 5% to 25% of individuals haveheritable muscular disorders. Muscle disorders
are very common in athletic horse breeds because,
surprisingly, they can also provide some beneficial
effects, ranging from enhanced muscle mass toeconomic metabolism.
Given the importance of the muscular system
to athletic performance of the horse, not surprisingly, it has attracted considerable research focus.
In the past two decades, “tying-up” up in athletic
horses has been teased into at least three distinct
disorders, which are heritable and therefore tend
to have strong breed predispositions. Several otherheritable muscular disorders of horses have also
been defined, causing problems ranging fromprofound weakness to respiratory paralysis andearly neonatal death. Advances in medicine now
permit convenient hair or blood tests for manyof these diseases due to their genetic basis, andbreeders are encouraged to display appropriate
stewardship by testing their breeding stock for
known disorders that have scientifically validated
genetic tests available. Current research efforts
are attempting to identify the genetic signatureof the disease causing tying-up in Thoroughbreds
and Standardbreds, which has proved challenging,and the disease causing tying-up in Arabian horses.
Advanced molecular techniques are also being applied to some disorders to determine exactly whatgoes wrong at the cellular level, to help define
the basis of clinical signs and to better direct thedevelopment of effective genetic tests.
Currently, the most clearly defined musculardisorders of athletic breeds are polysaccharide
storage myopathy (PSSM), hyperkalemic periodic
paralysis (HYPP), and glycogen branching enzyme
deficiency (GBED), because the cellular nature ofthese diseases and the underlying causative genetic
mutations are largely defined. PSSM is common
in Quarter horses and related breeds, and typicallycauses signs of tying-up. It is also linked to highbody condition, which can be desirable in those
breeds. HYPP causes weakness and paralysis and,occasionally, death. It is also associated with highmuscle mass, and therefore became prevalent due
to positive selection pressure for this trait. GBED
is an inevitably fatal disorder of Quarter Horses
and Paints, causing weakness and death in thefirst days to weeks of life. It is uncommon, andassociation with a positive trait is not recognized.
All three of these disorders can be readily tested
for on hair or blood.
Standardbred and Thoroughbred horses appear
to share a disorder causing tying-up during training, with clinical signs rarely or never seen during
actual racing exercise. This disease is referred to asrecurrent exertional rhabdomyolysis (RER). It appears to be more common in faster horses because
it might permit more rapid muscular processes atthe cellular level, hence there has been positive
selection pressure on this disease. The geneticsof RER have proven frustrating to define despite
many years of work. Warmblood and Arabianhorses might also share a disorder recently coined
as “myofibrillar myopathy” (MFM). Signs of thisdisease appear to consist of tying-up in Arabianhorses, and poor performance and poorly defined
movement abnormalities in Warmblood horses.
The genetic cause of MFM is not known and no
scientifically validated genetic tests exist for MFM
or RER.
In summary, muscular disorders are common
in athletic horses, and can be frustrating andeven fatal under some circumstances. Association
with specific positive traits has contributed to theprevalence of some of these diseases. Genetic testing is available for many heritable equine diseases,
and it is likely that testing for less clearly defineddisorders will be developed in the coming years.
Genetic stewardship relies on breeders being educated about heritable disorders, and performing
proactive breeding selection processes to produce
horses that are not only high performers but also
genetically sound.
CONTACT:
Erica McKenzie, BSc, BVMS, PhD, DACVIM, DACVSMR
erica.mckenzie@oregonstate.edu(541) 737-2858
Carlson College of Veterinary Medicine
Oregon State University
Corvallis, OREquine Disease Quarterly Newsletter

5
KENTUCKY

Equine Renal DiseaseRenal function is an important componentof overall health in any species. The kidneys
perform several important functions, including
waste removal, electrolyte balance, blood pressure
maintenance, a calcium source for bone health andproduction of factors for red blood cell stimulation, to name a few. In addition, the kidneys
receive substantial blood flow— approximately
25% of the cardiac output. Therefore, changes inblood flow, either increased or decreased, can havea significant impact on renal health.
Equine necropsy cases submitted to the University of Kentucky Veterinary Diagnostic Laboratory(UKVDL) over an eight-year period (2010-2018)
were queried for diagnoses related to renal pathology. Equine fetuses, foals, and adults of a variety
of breeds were included. It was determined that
3.6% (386/10,541) of equine submissions had
some type of renal pathology. Of those diagnoses,
renal lesions were determined to be primary in
38% of cases (n=148), secondary to another process in 55% of cases (n=211), or incidental in 7%
of cases (n=27).
Significant processes associated with primary lesions included: inflammatory/infectious (95 cases);congenital (21 cases); neoplastic renal carcinoma/
adenocarcinoma (10 cases); nephroliths (10 cases);
toxic (four cases); trauma (one case); and othermiscellaneous (i.e. chronic renal failure, protein
losing nephropathy) conditions (seven cases).
Within the infectious/inflammatory group,
the most common cause was a bacterial pathogen
resulting in nephritis. The largest proportion ofcases was due to Leptospira interrogans infections
in fetuses. Leptospirosis is a cause of abortion that
often localizes to the kidney. Actinobacillus equuli
was another common bacterial isolate, most often
seen in neonatal foals and occasionally adults.
In foals, infection with A. equuli is colloquiallytermed “sleepy foal disease.” Routes of infection
for A. equuli include a contaminated umbilicus,
inhalation or ingestion. Several cases of bacterial
pyelonephritis were identified. Pyelonephritis is
inflammation of the renal pelvis that most often
results from an infection that extends up to thekidneys from the lower urinary tract (i.e. urinary
bladder). The most common bacterial isolates
identified from cases at the UKVDL included

Streptococcus zooepidemicus, Escherichia coli, andEnterococcus sp.
Lesions that comprised the congenital category
included renal dysplasia, renal agenesis, congenital
renal cysts or congenital hydronephrosis/hydroureter. While there have been proposed associations of hereditary or nutritional components fordevelopmental renal abnormalities in some species(i.e. dogs and pigs), in horses the pathogenesis ofthese congenital lesions remains to be elucidated.
Significant nephroliths (kidney stones) wereidentified in 10 horses. The stones were composedof calcium carbonate or a mixture of calcium carbonate with other minerals. Typically, horses withnephroliths remain asymptomatic until the stone
results in obstruction. Development of nephroliths
has been associated with any nidus of renal disease
including cysts, papillary necrosis, pyelonephritis
or neoplasia.
Papillary (medullary crest) necrosis due tosuspected long-term use of non-steroidal antiinflammatory drugs (NSAIDs) was identified inthree of the four cases in the toxic category. NSAIDs(i.e. phenylbutazone/bute and flunixin meglumine/
Banamine) are routinely used in horses for pain
management. NSAIDs work by inhibiting a specificgroup of enzymes, cyclooxygenase (COX), which
subsequently reduces inflammation. Unfortunately,other downstream effects of this pathway include
decreased production of prostaglandins. Specificcells located in the renal medulla produce prostaglandins that are mediators of blood flow to the tissue. Therefore, decreased prostaglandin production
results in impaired blood flow to the medulla andsubsequent necrosis. Other compounding factors
include dehydration and use of multiple NSAIDs.
Luckily, renal complications due to NSAIDs arewell described with the result that there is judicious
use of these medications in practice.
The equine kidney has a vital role in overall
health. A variety of disease processes can impair
renal function. Awareness of these diseases is important for equine health.
CONTACT:
Jennifer Janes, DVM, PhD
jennifer.janes@uky.edu(859) 257-8283
University of Kentucky Veterinary Diagnostic Laboratory
Lexington, KY

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099

Presorted Standard
US Postage Paid
Permit 51
Lexington KY

Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

OCTOBER 2018
Volume 27, Number 4

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
Second Quarter2018  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2National
Asian Longhorned
Tick . . . . . . . . . . . . . . . . . 3
Muscular Disordersof Athletic Horses .  .  .  . 4KentuckyEquine Renal
Disease .  .  .  .  .  .  .  .  .  .  .  .  .  . 5

College of Agriculture,
Food and Environment
Department of
Veterinary ScienceVector or arthropod-borne diseases represent
some of the most significant threats to humanand animal health in certain regions/countries of
the world. An ever-increasing number have spreadbeyond historically defined boundaries, in no smallpart as a result of continued expansion in international trade of live animals or animal products andbecause of global climate change. The worldwide
spread of two human pathogens, Chikungunya
and Zika viruses, from the African continent inrecent years illustrates the major difficulties confronting the global community in containing theseand other arthropod-borne diseases.
Within the realm of infectious diseases, it ismore relevant in today’s world to consider populations of humans and animals in different countries
as co-existing in a global context, blurring theboundaries and reach of national political interests.
We have in essence become an international community in which social media play a major role incommunicating information across a spectrum ofissues, including disease events.
Aside from what is known of the diversity andrange of particular disease vectors in the USA, there
is a need to be mindful of the possible introductionof a particular arthropod, e.g. tick or mosquito,that has never been recorded previously in the
country—in other words, an invasive species.
The article in this issue of the Quarterly on the
discovery of the Asian longhorned tick (Haemaphysalis longicornis) for the first time in the USA
highlights the challenges that can be presented byan invasive tick species. Although shown to be acompetent vector of various diseases in a number
of Pacific Rim countries, the potential competencyof this particular tick to transmit animal or humandiseases in the country remains to be established.
Within recent months there have also been reports of the introduction of invasive species ofmosquito (Ochlerotatus japonicus) into Spain andof ticks (Hyalomma marginatum and H. rufipes)
into Germany.
Although the discovery of H. longicornis wasreported for the first time in 2018, subsequent
investigations have shown that the tick had beenin the USA at least since 2013. The lesson to belearned from this latest experience is that muchgreater surveillance and monitoring of tick andinsect populations in general is needed to establish
the range and distribution of the various species
with potential to serve as competent vectors ofknown mosquito and tick-borne diseases of equids.
To better prepare ourselves for dealing with
future disease threats, resources need to be madeavailable to support the infrastructure for morecomprehensive vector and disease surveillance
programs in conjunction with improved capacity
to respond to major disease events. The risk ofsuch threats will increase inevitably with continued
growth in the globalization of trade and the influence of climate change on our environment andthe spread of vectors and vector-borne diseases.
An integral element to better prepare ourselves
for the next disease threat is the need for greaterawareness and better education of practicing veterinarians who are frequently the “first responders” indealing with a case/outbreak of a novel disease ora possible invasive ecto-parasite. Increased public
education and engagement is also important inaddressing any disease threat that may evolve.
CONTACT:
Peter J. Timoney, MVB, MS, PhD, FRCVS
ptimoney@uky.edu(859) 218-1094
Charles Issel, DVM, PhD
cissel@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

Equine Disease Quarterly Newsletter

5
KENTUCKY

Equine Renal DiseaseRenal function is an important componentof overall health in any species. The kidneys
perform several important functions, including
waste removal, electrolyte balance, blood pressure
maintenance, a calcium source for bone health andproduction of factors for red blood cell stimulation, to name a few. In addition, the kidneys
receive substantial blood flow— approximately
25% of the cardiac output. Therefore, changes inblood flow, either increased or decreased, can havea significant impact on renal health.
Equine necropsy cases submitted to the University of Kentucky Veterinary Diagnostic Laboratory(UKVDL) over an eight-year period (2010-2018)
were queried for diagnoses related to renal pathology. Equine fetuses, foals, and adults of a variety
of breeds were included. It was determined that
3.6% (386/10,541) of equine submissions had
some type of renal pathology. Of those diagnoses,
renal lesions were determined to be primary in
38% of cases (n=148), secondary to another process in 55% of cases (n=211), or incidental in 7%
of cases (n=27).
Significant processes associated with primary lesions included: inflammatory/infectious (95 cases);congenital (21 cases); neoplastic renal carcinoma/
adenocarcinoma (10 cases); nephroliths (10 cases);
toxic (four cases); trauma (one case); and othermiscellaneous (i.e. chronic renal failure, protein
losing nephropathy) conditions (seven cases).
Within the infectious/inflammatory group,
the most common cause was a bacterial pathogen
resulting in nephritis. The largest proportion ofcases was due to Leptospira interrogans infections
in fetuses. Leptospirosis is a cause of abortion that
often localizes to the kidney. Actinobacillus equuli
was another common bacterial isolate, most often
seen in neonatal foals and occasionally adults.
In foals, infection with A. equuli is colloquiallytermed “sleepy foal disease.” Routes of infection
for A. equuli include a contaminated umbilicus,
inhalation or ingestion. Several cases of bacterial
pyelonephritis were identified. Pyelonephritis is
inflammation of the renal pelvis that most often
results from an infection that extends up to thekidneys from the lower urinary tract (i.e. urinary
bladder). The most common bacterial isolates
identified from cases at the UKVDL included

Streptococcus zooepidemicus, Escherichia coli, andEnterococcus sp.
Lesions that comprised the congenital category
included renal dysplasia, renal agenesis, congenital
renal cysts or congenital hydronephrosis/hydroureter. While there have been proposed associations of hereditary or nutritional components fordevelopmental renal abnormalities in some species(i.e. dogs and pigs), in horses the pathogenesis ofthese congenital lesions remains to be elucidated.
Significant nephroliths (kidney stones) wereidentified in 10 horses. The stones were composedof calcium carbonate or a mixture of calcium carbonate with other minerals. Typically, horses withnephroliths remain asymptomatic until the stone
results in obstruction. Development of nephroliths
has been associated with any nidus of renal disease
including cysts, papillary necrosis, pyelonephritis
or neoplasia.
Papillary (medullary crest) necrosis due tosuspected long-term use of non-steroidal antiinflammatory drugs (NSAIDs) was identified inthree of the four cases in the toxic category. NSAIDs(i.e. phenylbutazone/bute and flunixin meglumine/
Banamine) are routinely used in horses for pain
management. NSAIDs work by inhibiting a specificgroup of enzymes, cyclooxygenase (COX), which
subsequently reduces inflammation. Unfortunately,other downstream effects of this pathway include
decreased production of prostaglandins. Specificcells located in the renal medulla produce prostaglandins that are mediators of blood flow to the tissue. Therefore, decreased prostaglandin production
results in impaired blood flow to the medulla andsubsequent necrosis. Other compounding factors
include dehydration and use of multiple NSAIDs.
Luckily, renal complications due to NSAIDs arewell described with the result that there is judicious
use of these medications in practice.
The equine kidney has a vital role in overall
health. A variety of disease processes can impair
renal function. Awareness of these diseases is important for equine health.
CONTACT:
Jennifer Janes, DVM, PhD
jennifer.janes@uky.edu(859) 257-8283
University of Kentucky Veterinary Diagnostic Laboratory
Lexington, KY

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099
Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

OCTOBER 2018
Volume 27, Number 4

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
Second Quarter2018  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2National
Asian Longhorned
Tick . . . . . . . . . . . . . . . . . 3
Muscular Disordersof Athletic Horses  .  .  . 4KentuckyEquine Renal
Disease .  .  .  .  .  .  .  .  .  .  .  .  .  . 5

College of Agriculture,
Food and Environment
Department of
Veterinary ScienceVector or arthropod-borne diseases represent
some of the most significant threats to humanand animal health in certain regions/countries of
the world. An ever-increasing number have spreadbeyond historically defined boundaries, in no smallpart as a result of continued expansion in international trade of live animals or animal products andbecause of global climate change. The worldwide
spread of two human pathogens, Chikungunya
and Zika viruses, from the African continent inrecent years illustrates the major difficulties confronting the global community in containing theseand other arthropod-borne diseases.
Within the realm of infectious diseases, it ismore relevant in today’s world to consider populations of humans and animals in different countries
as co-existing in a global context, blurring theboundaries and reach of national political interests.
We have in essence become an international community in which social media play a major role incommunicating information across a spectrum ofissues, including disease events.
Aside from what is known of the diversity andrange of particular disease vectors in the USA, there
is a need to be mindful of the possible introductionof a particular arthropod, e.g. tick or mosquito,that has never been recorded previously in the
country—in other words, an invasive species.
The article in this issue of the Quarterly on the
discovery of the Asian longhorned tick (Haemaphysalis longicornis) for the first time in the USA
highlights the challenges that can be presented byan invasive tick species. Although shown to be acompetent vector of various diseases in a number
of Pacific Rim countries, the potential competencyof this particular tick to transmit animal or humandiseases in the country remains to be established.
Within recent months there have also been reports of the introduction of invasive species ofmosquito (Ochlerotatus japonicus) into Spain andof ticks (Hyalomma marginatum and H. rufipes)
into Germany.
Although the discovery of H. longicornis wasreported for the first time in 2018, subsequent
investigations have shown that the tick had beenin the USA at least since 2013. The lesson to belearned from this latest experience is that muchgreater surveillance and monitoring of tick andinsect populations in general is needed to establish
the range and distribution of the various species
with potential to serve as competent vectors ofknown mosquito and tick-borne diseases of equids.
To better prepare ourselves for dealing with
future disease threats, resources need to be madeavailable to support the infrastructure for morecomprehensive vector and disease surveillance
programs in conjunction with improved capacity
to respond to major disease events. The risk ofsuch threats will increase inevitably with continued
growth in the globalization of trade and the influence of climate change on our environment andthe spread of vectors and vector-borne diseases.
An integral element to better prepare ourselves
for the next disease threat is the need for greaterawareness and better education of practicing veterinarians who are frequently the “first responders” indealing with a case/outbreak of a novel disease ora possible invasive ecto-parasite. Increased public
education and engagement is also important inaddressing any disease threat that may evolve.
CONTACT:
Peter J. Timoney, MVB, MS, PhD, FRCVS
ptimoney@uky.edu(859) 218-1094
Charles Issel, DVM, PhD
cissel@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY