Equine Disease Quarterly Newsletter

Screwworm Myiasis

5M

yiasis is the infestation of vertebrate animals
by larvae (maggots) of any species of fly.
Some fly species are specialized to use amphibian, reptilian, or avian hosts, but most usually
infest mammals. In horses, the typical and mostwidespread of such parasites are species of internal bot flies (Gasterophilus spp.), but many othermaggots (e.g. blow flies and/or flesh flies) may
facultatively infest equines externally. Althoughnone of these typically poses a serious threat tohosts, screwworms are a separate and often dire
exception. Unlike the others, the New World
screwworm, Cochliomyia hominivorax, is a specialized native blow fly and obligate parasite whose
maggots voraciously feed only on living tissues ofwarm-blooded animals. It once occupied most of
the Neotropical Region, including South Texas
and South Florida, where it was historically thescourge of both wildlife and livestock. From its
winter refuges, it spread variably northwards
each summer and injured or killed thousands ofvictims yearly, causing substantial economic losses
to animal agriculture. In the mid-1900s, USDA
scientists conceived and began field-testing an innovative method aimed at eradicating screwworms
as pests. The so-called sterile insect technique (SIT)
involved mass-rearing millions of adult flies in
captivity, sterilizing them by exposure to radiation,and over-flooding wild screwworm populations

with sterile insects to the point that most local,
field-mated wild females produced inviable eggs.
Within several generations of such pressure, local
populations died out, and progressively screwworms were extirpated, first from the USA andeventually down to Panama by 2000. Screwworms
persist on a handful of Caribbean islands and innorthern South America, but they are prevented
from dispersing and re-infesting North America
by continuous releases of sterile flies in an eastern
Panamanian barrier zone. The last locally infested
animal in the U.S. was seen in 1982 in Texas,
and since then, dozens of screwworm incursions
have been detected and dealt with on animals andhumans entering the country from still-infested
areas. Many of these cases involved race horses orpolo ponies entering from South America, withscrewworms detected in quarantine facilities. Currently, however, an active invasive population ofscrewworms has taken up residence in the Florida
Keys. How these flies entered the country andfrom where is still a mystery, but the infestation isof particular concern because most of the known
infested hosts have been endangered Florida Key
deer on the National Key Deer Refuge. As of thiswriting, screwworms have killed approximately
10% of the Key deer herd, along with several local pet pigs, cats, and dogs. Since the infestation
was first discovered at the end of September 2016,

Presorted Standard
US Postage Paid
Permit 51
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

JANUARY 2017
Volume 26, Number 1

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
Third Quarter2016  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Equine Lameness .  .  .  . 3National
Equine Coronavirus . . 3
Screwworm Myiasis  . 4

personnel in a state/federal task force have instituted several strategies to contain and eliminate
screwworms from the Keys, including monitoringand surveillance of fly and maggot activities todelimit the infested area, veterinary inspectionsof all animals leaving the Keys, preventative andcurative treatments of animal hosts, and mostimportantly, local application of the SIT throughrelease of over 25 million sterile flies flown in fromPanama. Judicious continuation of these practices
into early 2017 is expected to prevent the spreadof screwworms, extirpate them, and once again,
make the USA screwworm free.
Contact:
James W. Mertins, MS, PhD, Entomologist
James.W.Mertin@aphis.usda.gov(515) 337-7919
USDA APHIS VS STAS; National Veterinary Services
Laboratories
Ames, Iowa

Commentary, continued from page 1.

Photos by
Matt Barton,
University of
Kentucky

So, how can we facilitate further progress inaddressing equine lameness challenges? A very
important part of the answer is quality scientificresearch to advance knowledge. At the Universityof Kentucky, we have established the EquestrianSports Research Initiative to enable multidisciplinary research teams to work together collaboratively with industry groups, clinical veterinarians,
and horse professionals. Health and welfare issues
in equine sports medicine are being studied frombasic to clinical levels by considering horse, rider,and surface issues concurrently. As noted above,scientific and technological advances are driving
progress in biomedical disciplines. Objective scientific research and the resulting new knowledge
are absolutely key, and need to be a top priority.
Contact:
James N. MacLeod, VMD, PhD
jnmacleod@uky.edu(859) 218-1099
Maxwell H. Gluck Equine Research Center
University of Kentucky, Lexington, KY

College of Agriculture,
Food and Environment
Department of
Veterinary Science

Accelerating Medical Progress on Equine LamenessIn the horse world, lameness is a major problem.
On this point, everyone agrees. Whether yourfocus is elite equine athletes or pleasure horses,
whether you are a professional or a recreational
rider, whether your primary breed of interest islarge or small, musculoskeletal injuries are common and potentially very serious.
Substantial progress has been made over the last
several decades in areas of both lameness diagnosis
and treatment. Importantly, the future holds asmuch promise as ever. Science and technology arecontinuing to drive advances in clinical disciplines.
Cell biology is a good example. With next
generation sequencing applied on a genomic scale(inclusive of all DNA or all RNA), it is now possible to broadly compare gene expression between
individual tissues and cell types. Data-driven scientific approaches are discovering a large numberof genes that nobody realized were important. The
results are providing new insights into cellular
identity, normal function, and disease mechanisms
in areas that have direct relevance to lameness.
New understanding about individual cell types
enables diagnostic and therapeutic strategies tobe refined. Consider cartilage as an example.
Our bodies contain several different cartilaginous
tissues—joint (articular) cartilage, non-articular
structural cartilage, cartilage that is replaced bybone through a process called endochondral ossification, and others. Although all types of cartilage
have features in common, an understanding of theunique cellular characteristics that define articularchondrocytes is clearly an important parameter toconsider with joint diseases.

Going forward, veterinarians will increasingly
have access to molecular biomarker panels to help
refine their list of differential diagnoses, to selectoptimal therapies, and for patient monitoring. We
already hear about these approaches with cancer
patients, and the same concepts are applicable forbone, cartilage, tendon, ligament, and muscle tissues. The clinical goals include improved sensitivity
in monitoring health as well as early identificationof disease problems and how the patient is responding to treatment.
On a therapeutic level, cell-based approaches
are generating high levels of interest and for goodreasons. The term “stem cells” is mentioned frequently. Cells can be used therapeutically to deliver
beneficial equine-specific growth and differentiation factors to an area of injury, to modulate thepatient’s immune system in helpful ways, and insome cases to directly generate a repair tissue. Thereis much to learn and quite a bit of misinformation
being disseminated, but cell-based therapies do
indeed hold a lot of promise.
Finally, we have entered the era of medical
informatics. Hardware, software, and data storage
options in computer science have advanced rapidly
to enable “big data” analyses that resolve biomedical relationships and patterns from “-omic” andpopulation levels that would be very hard to appreciate by looking only at an individual gene ora single patient. By analogy, consider how difficult
it would be to resolve crop circles and other patterns in a grain field while standing on the ground.
They are much easier to appreciate while looking
out the window of an airplane. It is not an “either/or” issue—broad and targeted analyses are both
important and often complementary.
continued on page 6.

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

N AT I O N A L

Third Quarter 2016

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross

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://www.ca.uky.edu/
gluck/index.htm
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

he International Collating Centre, Newmarket, United Kingdom and other sources
reported the following disease outbreaks.
Republic of South Africa reported outbreaksof African horse sickness in endemic areas of thecountry, but none in the Western Cape controlledzone.
Equine influenza was recorded in Germany(isolated case), the U.K. (case in an unvaccinatedfilly), and the USA, in which the disease is endemic. Outbreaks of the disease were confirmed
in California, Delaware, Florida, Kentucky, New
Jersey, and New York.
Strangles was reported by France, Germany,
Ireland, Singapore, and the USA. The number ofoutbreaks varied from four in France, twelve inGermany (all isolated cases), nineteen cases on two
premises in Ireland, a single case in an imported
horse in Singapore, and multiple outbreaks involving seventeen states in the USA. Outbreaks within
the USA consisted of 99 cases confirmed on an
estimated 36 premises, one of which represented
co-infection with equine herpesvirus 4.
France and South Africa recorded outbreaks ofequine herpesvirus 1 (EHV-1) infection. In the caseof the former, hyperthermia was the only clinicalsign observed. Clinical details were not provided
for the outbreak in South Africa. Outbreaks of
EHV-1 abortion were reported by Ireland, South
Africa and the UK, all involving isolated cases ofthe disease. EHV-1 related neurologic disease wasconfirmed in France, South Africa and the USA,each represented by single cases of the disease.
Respiratory disease caused by EHV-4 was recorded by France (seven outbreaks), South Africa
and Switzerland (single case of infection), and theUK (two outbreaks; limited number of infectedhorses in each instance). Germany reported acase of neurologic disease from which EHV-4 wasdetected from a nasal swab.
Infection with EHV-2 and/or EHV-5 was
confirmed in the USA, principally associated withevidence of respiratory disease.
Equine infectious anemia was recorded in
Canada and the USA. Nine cases were diagnosed
on three premises in Saskatchewan Province,

Canada. Two cases were confirmed on each of two
premises in New York and Oklahoma, USA.
France recorded that equine piroplasmosis wasendemic in the country. In the USA, Theileriaequi infection was confirmed in Quarter horse
racehorses engaged in non-sanctioned racing in
Tennessee (seventeen cases) and Wyoming/Utah(21 cases).
Germany reported nine cases of CEM on eightpremises, the majority in stallions and horses of
the Icelandic breed.
The USA reported cases/outbreaks of salmonellosis during the third quarter. Two cases involved
serogroup B Salmonella spp., 10 with serogroup
C1 spp. and two with serogroup D1 spp.
Outbreaks of clostridial enteritis due to Clostridium perfringens Type A, genotyped as β-2
toxin positive, were recorded by the USA, two in
Kentucky and two in Minnesota.
France and Germany confirmed limited outbreaks of rotavirus infection in foals.
One case of infection with Lawsonia intracellularis was diagnosed in a foal in Kentucky, USA.
Single cases of rabies were recorded in Oklahoma and Florida, USA.
The USA reported 49 cases of Eastern equine
encephalomyelitis during the period under review.
The greatest numbers of cases were confirmed in
Florida, Wisconsin, and South Carolina.
The USA confirmed a total of 88 cases of West
Nile encephalitis involving seventeen states. The
vast majority were in non-vaccinated horses or
those with incomplete vaccination histories.
Rhodococcus related disease was considered
endemic in the USA. Notwithstanding the factthat it is very difficult to estimate the prevalenceof this infection, some 40 cases were confirmed
during the third quarter.
Japan confirmed eight cases of Getah virus
infection on one premises, the majority having
incomplete vaccination histories. Infected horses
displayed typical clinical signs of the disease.
The USA reported three cases of Equine Monocytic Ehrlichiosis in Maryland and West Virginia.
Isolated cases of Ehrlichiosis were also confirmedin Germany and Switzerland.

Observation, Science, and Equine Lameness DiagnosisAsignificant number of pain-related gait abnormalities in horses are evident only when
the horse is ridden, and are not apparent when
the horse is hand-walked or lunged. Even whenthese horses are ridden, the lameness may not be
overt. While there have been many recent technicaladvancements in the objective assessment of gait,these are generally of limited value for detectionof bilaterally symmetrical alterations in gait that
result in reduced performance such as generalized
stiffness, lack of willingness to work, alteration inquality of movements such as lack of hindlimb
engagement and impulsion, and alteration in therider’s feel of the contact via the reins and bit tothe horse’s mouth.
A rider often assumes that these problems are
attributable to thoracolumbar region pain, because
the problems are only manifest when the horse isridden. When observed on the lunge, such horses
may lean into the circle—often more on one rein
than the other—and show exaggerated contractions of the epaxial muscles. However, studies
have shown that experimentally induced forelimbor hindlimb lameness may reduce range of motion of the thoracolumbosacral vertebral column.
Radiographic examination may reveal impinging
spinous processes, and this finding often results
in an erroneous conclusion implicating thoracolumbar pain as the primary problem. We havedemonstrated that by using diagnostic analgesia
to abolish overt or subclinical lameness, the rider
often appreciates an increased range of motion of
the horse’s back.
To investigate these clinical observations, wehave studied normal horses subjectively free fromlameness in hand, after flexion test, on the lunge
on both soft and firm surfaces and when ridden.
We objectively measured body lean on the lunge
and range of movement of the thoracolumbar
region using inertial measurement units placed at
predefined locations on the thoracolumbar andpelvic regions. These studies established normal
ranges of motion for the thoracolumbosacral
spine and demonstrated that sound horses have asmall degree of bilaterally symmetrical body leanon the lunge. We also measured body lean on thelunge in lame horses and demonstrated that there
is frequently asymmetry between left and rightreins, with greater lean compared with normal

on at least one rein. Substantial improvement
in lameness by performing diagnostic analgesia
resulted in reduced body lean on both reins andreestablishment of symmetry between left andright reins. Likewise, when lameness was improvedby diagnostic analgesia, range of motion of thethoracolumbosacral regions increased, especiallyin the caudal thoracic and lumbar regions.
We have observed that the tendency of a saddle
to slip persistently to one side is most frequently
associated with hindlimb lameness. Abolition oflameness by diagnostic analgesia results in resolution of the saddle slip. The saddle most commonly
slips to the side of the lame or more lame hindlimb,
but less frequently slips toward the less lame limb.
Presumably saddle slip is induced by altered rangeof motion of the thoracolumbosacral region, which
may vary among horses. Saddle slip may actually
be an indicator of the likely presence of hindlimb
lameness.
Overt lameness may not be apparent when ahorse is trotting, but musculoskeletal pain may
be manifest at a canter by the horse’s tendency to
become disunited or repeatedly change leading
limbs behind or in front, crookedness, loss of anormal three time rhythm, placing the hindlimbs
either abnormally close together spatially and temporally, or placing the limbs remarkably far apart.
These observations may be apparent either on thelunge or when the horse is ridden. Abolition of
baseline lameness seen in hand may paradoxicallymake the canter appear worse if sacroiliac pain iscontributing to pain and poor performance.
These observations highlight the importanceof evaluating horses with performance problems
both in hand, on the lunge and ridden, preferably
by the normal rider. Horses should be assessed inwalk, trot, and canter, bearing in mind that while
one aspect of the gait may improve with diagnostic
analgesia, another may deteriorate. Horses should
also be assessed performing the movements which
they find most difficult, because in some horses
this may be the only condition when the problem
is manifest.
Contact:
Sue Dyson, MA, VetMB, PhD, DEO, FRCVS
sue.dyson@aht.org.uk+44 (0)1638 7519098
Centre for Equine Studies, Animal Health Trust
Newmarket, Suffolk, UK

Equine Coronavirus – An Emerging Enteric Virus of Adult Horses

E

quine coronavirus (ECoV) is classified within
the Betacoronavirus genus, along with bovine
coronavirus, porcine hemagglutinating encephalomyelitis virus, mouse hepatitis virus, rat coronavirus (sialodacryoadenitis virus), and certain humancoronaviruses such as OC43, HKU1, Severe AcuteRespiratory Syndrome coronavirus, and Middle
East Respiratory Syndrome coronavirus; the latter two viruses have caused epidemic outbreaks ofrespiratory disease in human beings in the last decade. ECoV has been recently associated clinicallyand epidemiologically with emerging outbreaksof pyrogenic and enteric disease in adult horses
in Japan and anorexia, lethargy, and fever in the
United States.
Coronavirus infection typically begins in theproximal small intestine and subsequently spreads
to the colonic epithelial cells, leading to blunting of
the intestinal villi and subsequent villous atrophy.
Loss of epithelial cells results in malabsorption
and maldigestion of nutrients and acute diarrhea.
Following a short incubation period of 48-72
hours, adult horses develop fever, anorexia, anddepression. Changes in fecal character, ranging
from soft-formed stools to watery consistency,
and colic are seen in less than 20% of affectedhorses. A small number of horses develop acuteneurologic signs due to hyperammonemia, which
may manifest as severe depression, head pressing,
ataxia, proprioceptive deficits, recumbency, nystagmus, and seizure. Common hematological abnormalities are leucopenia due to neutropenia and/or
lymphopenia. ECoV infection generally resolves
within 1-4 days with supportive care consistingof the administration of anti-inflammatory drugs
and oral or intravenous fluids. Fatalities have been
associated with septicemia, endotoxemia as well as
metabolic abnormalities leading to encephalopathy(hyperammonemia).
Historically, the detection of ECoV has reliedon either electron microscopy, antigen-capture
ELISA, or viral isolation from the feces. All of thesedetection modalities lack sensitivity, especially if

viral particles are not present in sufficient numbers.
Quantitative polymerase chain reaction (PCR)
assay for the detection of ECoV nucleic acid has
supplanted many conventional virological assays,
mainly due to its short turn-around-time, highthroughput capability and increased analyticalsensitivity and specificity. The overall agreement
between clinical status and PCR results for ECoV
is over 90%, making fecal PCR the diagnostic toolof choice.
Infected horses can shed ECoV up to 14 days.
Due to the fecal-oral transmission route and thehighly infectious nature of ECoV, common-sense
biosecurity protocols should be instituted during
an outbreak of ECoV. ECoV PCR positive horses(clinical or subclinical) should always be isolated
from the rest of the equine population to decrease
the exposure risk and environmental contamination. Potentially exposed horses should not be
moved until their definitive infection status has
been determined. For isolation purposes, use an
empty barn or an isolation unit. In a barn situation,
close one end of the barn and use it as isolation
area. Caretakers and owners should wear gloves,protective clothing (coveralls or disposable gowns),
and dedicated footwear.
Good hand hygiene should be instituted (faucet
with warm/cold water or hand sanitizer).
Barrier nursing techniques should be established in the form of footbath or mats in front of
the isolation unit and each stall. This will minimize
the spread of pathogens from stalls to clean areas.
It is very important to control traffic and minimize
contact of affected horses with the general public.
Hygiene should be maximized by regular cleaningand disinfecting.
Contact:
Nicola Pusterla, DVM, PhD, Diplomate ACVIM
npusterla@ucdavis.edu(530) 752-1360
Department of Medicine and Epidemiology,
School of Veterinary Medicine
UC Davis, California

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

N AT I O N A L

Third Quarter 2016

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross

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://www.ca.uky.edu/
gluck/index.htm
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

he International Collating Centre, Newmarket, United Kingdom and other sources
reported the following disease outbreaks.
Republic of South Africa reported outbreaksof African horse sickness in endemic areas of thecountry, but none in the Western Cape controlledzone.
Equine influenza was recorded in Germany(isolated case), the U.K. (case in an unvaccinatedfilly), and the USA, in which the disease is endemic. Outbreaks of the disease were confirmed
in California, Delaware, Florida, Kentucky, New
Jersey, and New York.
Strangles was reported by France, Germany,
Ireland, Singapore, and the USA. The number ofoutbreaks varied from four in France, twelve inGermany (all isolated cases), nineteen cases on two
premises in Ireland, a single case in an imported
horse in Singapore, and multiple outbreaks involving seventeen states in the USA. Outbreaks within
the USA consisted of 99 cases confirmed on an
estimated 36 premises, one of which represented
co-infection with equine herpesvirus 4.
France and South Africa recorded outbreaks ofequine herpesvirus 1 (EHV-1) infection. In the caseof the former, hyperthermia was the only clinicalsign observed. Clinical details were not provided
for the outbreak in South Africa. Outbreaks of
EHV-1 abortion were reported by Ireland, South
Africa and the UK, all involving isolated cases ofthe disease. EHV-1 related neurologic disease wasconfirmed in France, South Africa and the USA,each represented by single cases of the disease.
Respiratory disease caused by EHV-4 was recorded by France (seven outbreaks), South Africa
and Switzerland (single case of infection), and theUK (two outbreaks; limited number of infectedhorses in each instance). Germany reported acase of neurologic disease from which EHV-4 wasdetected from a nasal swab.
Infection with EHV-2 and/or EHV-5 was
confirmed in the USA, principally associated withevidence of respiratory disease.
Equine infectious anemia was recorded in
Canada and the USA. Nine cases were diagnosed
on three premises in Saskatchewan Province,

Canada. Two cases were confirmed on each of two
premises in New York and Oklahoma, USA.
France recorded that equine piroplasmosis wasendemic in the country. In the USA, Theileriaequi infection was confirmed in Quarter horse
racehorses engaged in non-sanctioned racing in
Tennessee (seventeen cases) and Wyoming/Utah(21 cases).
Germany reported nine cases of CEM on eightpremises, the majority in stallions and horses of
the Icelandic breed.
The USA reported cases/outbreaks of salmonellosis during the third quarter. Two cases involved
serogroup B Salmonella spp., 10 with serogroup
C1 spp. and two with serogroup D1 spp.
Outbreaks of clostridial enteritis due to Clostridium perfringens Type A, genotyped as β-2
toxin positive, were recorded by the USA, two in
Kentucky and two in Minnesota.
France and Germany confirmed limited outbreaks of rotavirus infection in foals.
One case of infection with Lawsonia intracellularis was diagnosed in a foal in Kentucky, USA.
Single cases of rabies were recorded in Oklahoma and Florida, USA.
The USA reported 49 cases of Eastern equine
encephalomyelitis during the period under review.
The greatest numbers of cases were confirmed in
Florida, Wisconsin, and South Carolina.
The USA confirmed a total of 88 cases of West
Nile encephalitis involving seventeen states. The
vast majority were in non-vaccinated horses or
those with incomplete vaccination histories.
Rhodococcus related disease was considered
endemic in the USA. Notwithstanding the factthat it is very difficult to estimate the prevalenceof this infection, some 40 cases were confirmed
during the third quarter.
Japan confirmed eight cases of Getah virus
infection on one premises, the majority having
incomplete vaccination histories. Infected horses
displayed typical clinical signs of the disease.
The USA reported three cases of Equine Monocytic Ehrlichiosis in Maryland and West Virginia.
Isolated cases of Ehrlichiosis were also confirmedin Germany and Switzerland.

Observation, Science, and Equine Lameness DiagnosisAsignificant number of pain-related gait abnormalities in horses are evident only when
the horse is ridden, and are not apparent when
the horse is hand-walked or lunged. Even whenthese horses are ridden, the lameness may not be
overt. While there have been many recent technicaladvancements in the objective assessment of gait,these are generally of limited value for detectionof bilaterally symmetrical alterations in gait that
result in reduced performance such as generalized
stiffness, lack of willingness to work, alteration inquality of movements such as lack of hindlimb
engagement and impulsion, and alteration in therider’s feel of the contact via the reins and bit tothe horse’s mouth.
A rider often assumes that these problems are
attributable to thoracolumbar region pain, because
the problems are only manifest when the horse isridden. When observed on the lunge, such horses
may lean into the circle—often more on one rein
than the other—and show exaggerated contractions of the epaxial muscles. However, studies
have shown that experimentally induced forelimbor hindlimb lameness may reduce range of motion of the thoracolumbosacral vertebral column.
Radiographic examination may reveal impinging
spinous processes, and this finding often results
in an erroneous conclusion implicating thoracolumbar pain as the primary problem. We havedemonstrated that by using diagnostic analgesia
to abolish overt or subclinical lameness, the rider
often appreciates an increased range of motion of
the horse’s back.
To investigate these clinical observations, wehave studied normal horses subjectively free fromlameness in hand, after flexion test, on the lunge
on both soft and firm surfaces and when ridden.
We objectively measured body lean on the lunge
and range of movement of the thoracolumbar
region using inertial measurement units placed at
predefined locations on the thoracolumbar andpelvic regions. These studies established normal
ranges of motion for the thoracolumbosacral
spine and demonstrated that sound horses have asmall degree of bilaterally symmetrical body leanon the lunge. We also measured body lean on thelunge in lame horses and demonstrated that there
is frequently asymmetry between left and rightreins, with greater lean compared with normal

on at least one rein. Substantial improvement
in lameness by performing diagnostic analgesia
resulted in reduced body lean on both reins andreestablishment of symmetry between left andright reins. Likewise, when lameness was improvedby diagnostic analgesia, range of motion of thethoracolumbosacral regions increased, especiallyin the caudal thoracic and lumbar regions.
We have observed that the tendency of a saddle
to slip persistently to one side is most frequently
associated with hindlimb lameness. Abolition oflameness by diagnostic analgesia results in resolution of the saddle slip. The saddle most commonly
slips to the side of the lame or more lame hindlimb,
but less frequently slips toward the less lame limb.
Presumably saddle slip is induced by altered rangeof motion of the thoracolumbosacral region, which
may vary among horses. Saddle slip may actually
be an indicator of the likely presence of hindlimb
lameness.
Overt lameness may not be apparent when ahorse is trotting, but musculoskeletal pain may
be manifest at a canter by the horse’s tendency to
become disunited or repeatedly change leading
limbs behind or in front, crookedness, loss of anormal three time rhythm, placing the hindlimbs
either abnormally close together spatially and temporally, or placing the limbs remarkably far apart.
These observations may be apparent either on thelunge or when the horse is ridden. Abolition of
baseline lameness seen in hand may paradoxicallymake the canter appear worse if sacroiliac pain iscontributing to pain and poor performance.
These observations highlight the importanceof evaluating horses with performance problems
both in hand, on the lunge and ridden, preferably
by the normal rider. Horses should be assessed inwalk, trot, and canter, bearing in mind that while
one aspect of the gait may improve with diagnostic
analgesia, another may deteriorate. Horses should
also be assessed performing the movements which
they find most difficult, because in some horses
this may be the only condition when the problem
is manifest.
Contact:
Sue Dyson, MA, VetMB, PhD, DEO, FRCVS
sue.dyson@aht.org.uk+44 (0)1638 7519098
Centre for Equine Studies, Animal Health Trust
Newmarket, Suffolk, UK

Equine Coronavirus – An Emerging Enteric Virus of Adult Horses

E

quine coronavirus (ECoV) is classified within
the Betacoronavirus genus, along with bovine
coronavirus, porcine hemagglutinating encephalomyelitis virus, mouse hepatitis virus, rat coronavirus (sialodacryoadenitis virus), and certain humancoronaviruses such as OC43, HKU1, Severe AcuteRespiratory Syndrome coronavirus, and Middle
East Respiratory Syndrome coronavirus; the latter two viruses have caused epidemic outbreaks ofrespiratory disease in human beings in the last decade. ECoV has been recently associated clinicallyand epidemiologically with emerging outbreaksof pyrogenic and enteric disease in adult horses
in Japan and anorexia, lethargy, and fever in the
United States.
Coronavirus infection typically begins in theproximal small intestine and subsequently spreads
to the colonic epithelial cells, leading to blunting of
the intestinal villi and subsequent villous atrophy.
Loss of epithelial cells results in malabsorption
and maldigestion of nutrients and acute diarrhea.
Following a short incubation period of 48-72
hours, adult horses develop fever, anorexia, anddepression. Changes in fecal character, ranging
from soft-formed stools to watery consistency,
and colic are seen in less than 20% of affectedhorses. A small number of horses develop acuteneurologic signs due to hyperammonemia, which
may manifest as severe depression, head pressing,
ataxia, proprioceptive deficits, recumbency, nystagmus, and seizure. Common hematological abnormalities are leucopenia due to neutropenia and/or
lymphopenia. ECoV infection generally resolves
within 1-4 days with supportive care consistingof the administration of anti-inflammatory drugs
and oral or intravenous fluids. Fatalities have been
associated with septicemia, endotoxemia as well as
metabolic abnormalities leading to encephalopathy(hyperammonemia).
Historically, the detection of ECoV has reliedon either electron microscopy, antigen-capture
ELISA, or viral isolation from the feces. All of thesedetection modalities lack sensitivity, especially if

viral particles are not present in sufficient numbers.
Quantitative polymerase chain reaction (PCR)
assay for the detection of ECoV nucleic acid has
supplanted many conventional virological assays,
mainly due to its short turn-around-time, highthroughput capability and increased analyticalsensitivity and specificity. The overall agreement
between clinical status and PCR results for ECoV
is over 90%, making fecal PCR the diagnostic toolof choice.
Infected horses can shed ECoV up to 14 days.
Due to the fecal-oral transmission route and thehighly infectious nature of ECoV, common-sense
biosecurity protocols should be instituted during
an outbreak of ECoV. ECoV PCR positive horses(clinical or subclinical) should always be isolated
from the rest of the equine population to decrease
the exposure risk and environmental contamination. Potentially exposed horses should not be
moved until their definitive infection status has
been determined. For isolation purposes, use an
empty barn or an isolation unit. In a barn situation,
close one end of the barn and use it as isolation
area. Caretakers and owners should wear gloves,protective clothing (coveralls or disposable gowns),
and dedicated footwear.
Good hand hygiene should be instituted (faucet
with warm/cold water or hand sanitizer).
Barrier nursing techniques should be established in the form of footbath or mats in front of
the isolation unit and each stall. This will minimize
the spread of pathogens from stalls to clean areas.
It is very important to control traffic and minimize
contact of affected horses with the general public.
Hygiene should be maximized by regular cleaningand disinfecting.
Contact:
Nicola Pusterla, DVM, PhD, Diplomate ACVIM
npusterla@ucdavis.edu(530) 752-1360
Department of Medicine and Epidemiology,
School of Veterinary Medicine
UC Davis, California

2

3

4

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

N AT I O N A L

Third Quarter 2016

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross

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://www.ca.uky.edu/
gluck/index.htm
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

he International Collating Centre, Newmarket, United Kingdom and other sources
reported the following disease outbreaks.
Republic of South Africa reported outbreaksof African horse sickness in endemic areas of thecountry, but none in the Western Cape controlledzone.
Equine influenza was recorded in Germany(isolated case), the U.K. (case in an unvaccinatedfilly), and the USA, in which the disease is endemic. Outbreaks of the disease were confirmed
in California, Delaware, Florida, Kentucky, New
Jersey, and New York.
Strangles was reported by France, Germany,
Ireland, Singapore, and the USA. The number ofoutbreaks varied from four in France, twelve inGermany (all isolated cases), nineteen cases on two
premises in Ireland, a single case in an imported
horse in Singapore, and multiple outbreaks involving seventeen states in the USA. Outbreaks within
the USA consisted of 99 cases confirmed on an
estimated 36 premises, one of which represented
co-infection with equine herpesvirus 4.
France and South Africa recorded outbreaks ofequine herpesvirus 1 (EHV-1) infection. In the caseof the former, hyperthermia was the only clinicalsign observed. Clinical details were not provided
for the outbreak in South Africa. Outbreaks of
EHV-1 abortion were reported by Ireland, South
Africa and the UK, all involving isolated cases ofthe disease. EHV-1 related neurologic disease wasconfirmed in France, South Africa and the USA,each represented by single cases of the disease.
Respiratory disease caused by EHV-4 was recorded by France (seven outbreaks), South Africa
and Switzerland (single case of infection), and theUK (two outbreaks; limited number of infectedhorses in each instance). Germany reported acase of neurologic disease from which EHV-4 wasdetected from a nasal swab.
Infection with EHV-2 and/or EHV-5 was
confirmed in the USA, principally associated withevidence of respiratory disease.
Equine infectious anemia was recorded in
Canada and the USA. Nine cases were diagnosed
on three premises in Saskatchewan Province,

Canada. Two cases were confirmed on each of two
premises in New York and Oklahoma, USA.
France recorded that equine piroplasmosis wasendemic in the country. In the USA, Theileriaequi infection was confirmed in Quarter horse
racehorses engaged in non-sanctioned racing in
Tennessee (seventeen cases) and Wyoming/Utah(21 cases).
Germany reported nine cases of CEM on eightpremises, the majority in stallions and horses of
the Icelandic breed.
The USA reported cases/outbreaks of salmonellosis during the third quarter. Two cases involved
serogroup B Salmonella spp., 10 with serogroup
C1 spp. and two with serogroup D1 spp.
Outbreaks of clostridial enteritis due to Clostridium perfringens Type A, genotyped as β-2
toxin positive, were recorded by the USA, two in
Kentucky and two in Minnesota.
France and Germany confirmed limited outbreaks of rotavirus infection in foals.
One case of infection with Lawsonia intracellularis was diagnosed in a foal in Kentucky, USA.
Single cases of rabies were recorded in Oklahoma and Florida, USA.
The USA reported 49 cases of Eastern equine
encephalomyelitis during the period under review.
The greatest numbers of cases were confirmed in
Florida, Wisconsin, and South Carolina.
The USA confirmed a total of 88 cases of West
Nile encephalitis involving seventeen states. The
vast majority were in non-vaccinated horses or
those with incomplete vaccination histories.
Rhodococcus related disease was considered
endemic in the USA. Notwithstanding the factthat it is very difficult to estimate the prevalenceof this infection, some 40 cases were confirmed
during the third quarter.
Japan confirmed eight cases of Getah virus
infection on one premises, the majority having
incomplete vaccination histories. Infected horses
displayed typical clinical signs of the disease.
The USA reported three cases of Equine Monocytic Ehrlichiosis in Maryland and West Virginia.
Isolated cases of Ehrlichiosis were also confirmedin Germany and Switzerland.

Observation, Science, and Equine Lameness DiagnosisAsignificant number of pain-related gait abnormalities in horses are evident only when
the horse is ridden, and are not apparent when
the horse is hand-walked or lunged. Even whenthese horses are ridden, the lameness may not be
overt. While there have been many recent technicaladvancements in the objective assessment of gait,these are generally of limited value for detectionof bilaterally symmetrical alterations in gait that
result in reduced performance such as generalized
stiffness, lack of willingness to work, alteration inquality of movements such as lack of hindlimb
engagement and impulsion, and alteration in therider’s feel of the contact via the reins and bit tothe horse’s mouth.
A rider often assumes that these problems are
attributable to thoracolumbar region pain, because
the problems are only manifest when the horse isridden. When observed on the lunge, such horses
may lean into the circle—often more on one rein
than the other—and show exaggerated contractions of the epaxial muscles. However, studies
have shown that experimentally induced forelimbor hindlimb lameness may reduce range of motion of the thoracolumbosacral vertebral column.
Radiographic examination may reveal impinging
spinous processes, and this finding often results
in an erroneous conclusion implicating thoracolumbar pain as the primary problem. We havedemonstrated that by using diagnostic analgesia
to abolish overt or subclinical lameness, the rider
often appreciates an increased range of motion of
the horse’s back.
To investigate these clinical observations, wehave studied normal horses subjectively free fromlameness in hand, after flexion test, on the lunge
on both soft and firm surfaces and when ridden.
We objectively measured body lean on the lunge
and range of movement of the thoracolumbar
region using inertial measurement units placed at
predefined locations on the thoracolumbar andpelvic regions. These studies established normal
ranges of motion for the thoracolumbosacral
spine and demonstrated that sound horses have asmall degree of bilaterally symmetrical body leanon the lunge. We also measured body lean on thelunge in lame horses and demonstrated that there
is frequently asymmetry between left and rightreins, with greater lean compared with normal

on at least one rein. Substantial improvement
in lameness by performing diagnostic analgesia
resulted in reduced body lean on both reins andreestablishment of symmetry between left andright reins. Likewise, when lameness was improvedby diagnostic analgesia, range of motion of thethoracolumbosacral regions increased, especiallyin the caudal thoracic and lumbar regions.
We have observed that the tendency of a saddle
to slip persistently to one side is most frequently
associated with hindlimb lameness. Abolition oflameness by diagnostic analgesia results in resolution of the saddle slip. The saddle most commonly
slips to the side of the lame or more lame hindlimb,
but less frequently slips toward the less lame limb.
Presumably saddle slip is induced by altered rangeof motion of the thoracolumbosacral region, which
may vary among horses. Saddle slip may actually
be an indicator of the likely presence of hindlimb
lameness.
Overt lameness may not be apparent when ahorse is trotting, but musculoskeletal pain may
be manifest at a canter by the horse’s tendency to
become disunited or repeatedly change leading
limbs behind or in front, crookedness, loss of anormal three time rhythm, placing the hindlimbs
either abnormally close together spatially and temporally, or placing the limbs remarkably far apart.
These observations may be apparent either on thelunge or when the horse is ridden. Abolition of
baseline lameness seen in hand may paradoxicallymake the canter appear worse if sacroiliac pain iscontributing to pain and poor performance.
These observations highlight the importanceof evaluating horses with performance problems
both in hand, on the lunge and ridden, preferably
by the normal rider. Horses should be assessed inwalk, trot, and canter, bearing in mind that while
one aspect of the gait may improve with diagnostic
analgesia, another may deteriorate. Horses should
also be assessed performing the movements which
they find most difficult, because in some horses
this may be the only condition when the problem
is manifest.
Contact:
Sue Dyson, MA, VetMB, PhD, DEO, FRCVS
sue.dyson@aht.org.uk+44 (0)1638 7519098
Centre for Equine Studies, Animal Health Trust
Newmarket, Suffolk, UK

Equine Coronavirus – An Emerging Enteric Virus of Adult Horses

E

quine coronavirus (ECoV) is classified within
the Betacoronavirus genus, along with bovine
coronavirus, porcine hemagglutinating encephalomyelitis virus, mouse hepatitis virus, rat coronavirus (sialodacryoadenitis virus), and certain humancoronaviruses such as OC43, HKU1, Severe AcuteRespiratory Syndrome coronavirus, and Middle
East Respiratory Syndrome coronavirus; the latter two viruses have caused epidemic outbreaks ofrespiratory disease in human beings in the last decade. ECoV has been recently associated clinicallyand epidemiologically with emerging outbreaksof pyrogenic and enteric disease in adult horses
in Japan and anorexia, lethargy, and fever in the
United States.
Coronavirus infection typically begins in theproximal small intestine and subsequently spreads
to the colonic epithelial cells, leading to blunting of
the intestinal villi and subsequent villous atrophy.
Loss of epithelial cells results in malabsorption
and maldigestion of nutrients and acute diarrhea.
Following a short incubation period of 48-72
hours, adult horses develop fever, anorexia, anddepression. Changes in fecal character, ranging
from soft-formed stools to watery consistency,
and colic are seen in less than 20% of affectedhorses. A small number of horses develop acuteneurologic signs due to hyperammonemia, which
may manifest as severe depression, head pressing,
ataxia, proprioceptive deficits, recumbency, nystagmus, and seizure. Common hematological abnormalities are leucopenia due to neutropenia and/or
lymphopenia. ECoV infection generally resolves
within 1-4 days with supportive care consistingof the administration of anti-inflammatory drugs
and oral or intravenous fluids. Fatalities have been
associated with septicemia, endotoxemia as well as
metabolic abnormalities leading to encephalopathy(hyperammonemia).
Historically, the detection of ECoV has reliedon either electron microscopy, antigen-capture
ELISA, or viral isolation from the feces. All of thesedetection modalities lack sensitivity, especially if

viral particles are not present in sufficient numbers.
Quantitative polymerase chain reaction (PCR)
assay for the detection of ECoV nucleic acid has
supplanted many conventional virological assays,
mainly due to its short turn-around-time, highthroughput capability and increased analyticalsensitivity and specificity. The overall agreement
between clinical status and PCR results for ECoV
is over 90%, making fecal PCR the diagnostic toolof choice.
Infected horses can shed ECoV up to 14 days.
Due to the fecal-oral transmission route and thehighly infectious nature of ECoV, common-sense
biosecurity protocols should be instituted during
an outbreak of ECoV. ECoV PCR positive horses(clinical or subclinical) should always be isolated
from the rest of the equine population to decrease
the exposure risk and environmental contamination. Potentially exposed horses should not be
moved until their definitive infection status has
been determined. For isolation purposes, use an
empty barn or an isolation unit. In a barn situation,
close one end of the barn and use it as isolation
area. Caretakers and owners should wear gloves,protective clothing (coveralls or disposable gowns),
and dedicated footwear.
Good hand hygiene should be instituted (faucet
with warm/cold water or hand sanitizer).
Barrier nursing techniques should be established in the form of footbath or mats in front of
the isolation unit and each stall. This will minimize
the spread of pathogens from stalls to clean areas.
It is very important to control traffic and minimize
contact of affected horses with the general public.
Hygiene should be maximized by regular cleaningand disinfecting.
Contact:
Nicola Pusterla, DVM, PhD, Diplomate ACVIM
npusterla@ucdavis.edu(530) 752-1360
Department of Medicine and Epidemiology,
School of Veterinary Medicine
UC Davis, California

Equine Disease Quarterly Newsletter

Screwworm Myiasis

5M

yiasis is the infestation of vertebrate animals
by larvae (maggots) of any species of fly.
Some fly species are specialized to use amphibian, reptilian, or avian hosts, but most usually
infest mammals. In horses, the typical and mostwidespread of such parasites are species of internal bot flies (Gasterophilus spp.), but many othermaggots (e.g. blow flies and/or flesh flies) may
facultatively infest equines externally. Althoughnone of these typically poses a serious threat tohosts, screwworms are a separate and often dire
exception. Unlike the others, the New World
screwworm, Cochliomyia hominivorax, is a specialized native blow fly and obligate parasite whose
maggots voraciously feed only on living tissues ofwarm-blooded animals. It once occupied most of
the Neotropical Region, including South Texas
and South Florida, where it was historically thescourge of both wildlife and livestock. From its
winter refuges, it spread variably northwards
each summer and injured or killed thousands ofvictims yearly, causing substantial economic losses
to animal agriculture. In the mid-1900s, USDA
scientists conceived and began field-testing an innovative method aimed at eradicating screwworms
as pests. The so-called sterile insect technique (SIT)
involved mass-rearing millions of adult flies in
captivity, sterilizing them by exposure to radiation,and over-flooding wild screwworm populations

with sterile insects to the point that most local,
field-mated wild females produced inviable eggs.
Within several generations of such pressure, local
populations died out, and progressively screwworms were extirpated, first from the USA andeventually down to Panama by 2000. Screwworms
persist on a handful of Caribbean islands and innorthern South America, but they are prevented
from dispersing and re-infesting North America
by continuous releases of sterile flies in an eastern
Panamanian barrier zone. The last locally infested
animal in the U.S. was seen in 1982 in Texas,
and since then, dozens of screwworm incursions
have been detected and dealt with on animals andhumans entering the country from still-infested
areas. Many of these cases involved race horses orpolo ponies entering from South America, withscrewworms detected in quarantine facilities. Currently, however, an active invasive population ofscrewworms has taken up residence in the Florida
Keys. How these flies entered the country andfrom where is still a mystery, but the infestation isof particular concern because most of the known
infested hosts have been endangered Florida Key
deer on the National Key Deer Refuge. As of thiswriting, screwworms have killed approximately
10% of the Key deer herd, along with several local pet pigs, cats, and dogs. Since the infestation
was first discovered at the end of September 2016,

Presorted Standard
US Postage Paid
Permit 51
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

JANUARY 2017
Volume 26, Number 1

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
Third Quarter2016  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Equine Lameness .  .  .  . 3National
Equine Coronavirus . . 3
Screwworm Myiasis  . 4

personnel in a state/federal task force have instituted several strategies to contain and eliminate
screwworms from the Keys, including monitoringand surveillance of fly and maggot activities todelimit the infested area, veterinary inspectionsof all animals leaving the Keys, preventative andcurative treatments of animal hosts, and mostimportantly, local application of the SIT throughrelease of over 25 million sterile flies flown in fromPanama. Judicious continuation of these practices
into early 2017 is expected to prevent the spreadof screwworms, extirpate them, and once again,
make the USA screwworm free.
Contact:
James W. Mertins, MS, PhD, Entomologist
James.W.Mertin@aphis.usda.gov(515) 337-7919
USDA APHIS VS STAS; National Veterinary Services
Laboratories
Ames, Iowa

Commentary, continued from page 1.

Photos by
Matt Barton,
University of
Kentucky

So, how can we facilitate further progress inaddressing equine lameness challenges? A very
important part of the answer is quality scientificresearch to advance knowledge. At the Universityof Kentucky, we have established the EquestrianSports Research Initiative to enable multidisciplinary research teams to work together collaboratively with industry groups, clinical veterinarians,
and horse professionals. Health and welfare issues
in equine sports medicine are being studied frombasic to clinical levels by considering horse, rider,and surface issues concurrently. As noted above,scientific and technological advances are driving
progress in biomedical disciplines. Objective scientific research and the resulting new knowledge
are absolutely key, and need to be a top priority.
Contact:
James N. MacLeod, VMD, PhD
jnmacleod@uky.edu(859) 218-1099
Maxwell H. Gluck Equine Research Center
University of Kentucky, Lexington, KY

College of Agriculture,
Food and Environment
Department of
Veterinary Science

Accelerating Medical Progress on Equine LamenessIn the horse world, lameness is a major problem.
On this point, everyone agrees. Whether yourfocus is elite equine athletes or pleasure horses,
whether you are a professional or a recreational
rider, whether your primary breed of interest islarge or small, musculoskeletal injuries are common and potentially very serious.
Substantial progress has been made over the last
several decades in areas of both lameness diagnosis
and treatment. Importantly, the future holds asmuch promise as ever. Science and technology arecontinuing to drive advances in clinical disciplines.
Cell biology is a good example. With next
generation sequencing applied on a genomic scale(inclusive of all DNA or all RNA), it is now possible to broadly compare gene expression between
individual tissues and cell types. Data-driven scientific approaches are discovering a large numberof genes that nobody realized were important. The
results are providing new insights into cellular
identity, normal function, and disease mechanisms
in areas that have direct relevance to lameness.
New understanding about individual cell types
enables diagnostic and therapeutic strategies tobe refined. Consider cartilage as an example.
Our bodies contain several different cartilaginous
tissues—joint (articular) cartilage, non-articular
structural cartilage, cartilage that is replaced bybone through a process called endochondral ossification, and others. Although all types of cartilage
have features in common, an understanding of theunique cellular characteristics that define articularchondrocytes is clearly an important parameter toconsider with joint diseases.

Going forward, veterinarians will increasingly
have access to molecular biomarker panels to help
refine their list of differential diagnoses, to selectoptimal therapies, and for patient monitoring. We
already hear about these approaches with cancer
patients, and the same concepts are applicable forbone, cartilage, tendon, ligament, and muscle tissues. The clinical goals include improved sensitivity
in monitoring health as well as early identificationof disease problems and how the patient is responding to treatment.
On a therapeutic level, cell-based approaches
are generating high levels of interest and for goodreasons. The term “stem cells” is mentioned frequently. Cells can be used therapeutically to deliver
beneficial equine-specific growth and differentiation factors to an area of injury, to modulate thepatient’s immune system in helpful ways, and insome cases to directly generate a repair tissue. Thereis much to learn and quite a bit of misinformation
being disseminated, but cell-based therapies do
indeed hold a lot of promise.
Finally, we have entered the era of medical
informatics. Hardware, software, and data storage
options in computer science have advanced rapidly
to enable “big data” analyses that resolve biomedical relationships and patterns from “-omic” andpopulation levels that would be very hard to appreciate by looking only at an individual gene ora single patient. By analogy, consider how difficult
it would be to resolve crop circles and other patterns in a grain field while standing on the ground.
They are much easier to appreciate while looking
out the window of an airplane. It is not an “either/or” issue—broad and targeted analyses are both
important and often complementary.
continued on page 6.

Equine Disease Quarterly Newsletter

Screwworm Myiasis

5M

yiasis is the infestation of vertebrate animals
by larvae (maggots) of any species of fly.
Some fly species are specialized to use amphibian, reptilian, or avian hosts, but most usually
infest mammals. In horses, the typical and mostwidespread of such parasites are species of internal bot flies (Gasterophilus spp.), but many othermaggots (e.g. blow flies and/or flesh flies) may
facultatively infest equines externally. Althoughnone of these typically poses a serious threat tohosts, screwworms are a separate and often dire
exception. Unlike the others, the New World
screwworm, Cochliomyia hominivorax, is a specialized native blow fly and obligate parasite whose
maggots voraciously feed only on living tissues ofwarm-blooded animals. It once occupied most of
the Neotropical Region, including South Texas
and South Florida, where it was historically thescourge of both wildlife and livestock. From its
winter refuges, it spread variably northwards
each summer and injured or killed thousands ofvictims yearly, causing substantial economic losses
to animal agriculture. In the mid-1900s, USDA
scientists conceived and began field-testing an innovative method aimed at eradicating screwworms
as pests. The so-called sterile insect technique (SIT)
involved mass-rearing millions of adult flies in
captivity, sterilizing them by exposure to radiation,and over-flooding wild screwworm populations

with sterile insects to the point that most local,
field-mated wild females produced inviable eggs.
Within several generations of such pressure, local
populations died out, and progressively screwworms were extirpated, first from the USA andeventually down to Panama by 2000. Screwworms
persist on a handful of Caribbean islands and innorthern South America, but they are prevented
from dispersing and re-infesting North America
by continuous releases of sterile flies in an eastern
Panamanian barrier zone. The last locally infested
animal in the U.S. was seen in 1982 in Texas,
and since then, dozens of screwworm incursions
have been detected and dealt with on animals andhumans entering the country from still-infested
areas. Many of these cases involved race horses orpolo ponies entering from South America, withscrewworms detected in quarantine facilities. Currently, however, an active invasive population ofscrewworms has taken up residence in the Florida
Keys. How these flies entered the country andfrom where is still a mystery, but the infestation isof particular concern because most of the known
infested hosts have been endangered Florida Key
deer on the National Key Deer Refuge. As of thiswriting, screwworms have killed approximately
10% of the Key deer herd, along with several local pet pigs, cats, and dogs. Since the infestation
was first discovered at the end of September 2016,

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

JANUARY 2017
Volume 26, Number 1

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
Third Quarter2016  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Equine Lameness  .  .  . 3National
Equine Coronavirus . . 3
Screwworm Myiasis  . 4

personnel in a state/federal task force have instituted several strategies to contain and eliminate
screwworms from the Keys, including monitoringand surveillance of fly and maggot activities todelimit the infested area, veterinary inspectionsof all animals leaving the Keys, preventative andcurative treatments of animal hosts, and mostimportantly, local application of the SIT throughrelease of over 25 million sterile flies flown in fromPanama. Judicious continuation of these practices
into early 2017 is expected to prevent the spreadof screwworms, extirpate them, and once again,
make the USA screwworm free.
Contact:
James W. Mertins, MS, PhD, Entomologist
James.W.Mertin@aphis.usda.gov(515) 337-7919
USDA APHIS VS STAS; National Veterinary Services
Laboratories
Ames, Iowa

Commentary, continued from page 1.

Photos by
Matt Barton,
University of
Kentucky

So, how can we facilitate further progress inaddressing equine lameness challenges? A very
important part of the answer is quality scientificresearch to advance knowledge. At the Universityof Kentucky, we have established the EquestrianSports Research Initiative to enable multidisciplinary research teams to work together collaboratively with industry groups, clinical veterinarians,
and horse professionals. Health and welfare issues
in equine sports medicine are being studied frombasic to clinical levels by considering horse, rider,and surface issues concurrently. As noted above,scientific and technological advances are driving
progress in biomedical disciplines. Objective scientific research and the resulting new knowledge
are absolutely key, and need to be a top priority.
Contact:
James N. MacLeod, VMD, PhD
jnmacleod@uky.edu(859) 218-1099
Maxwell H. Gluck Equine Research Center
University of Kentucky, Lexington, KY

College of Agriculture,
Food and Environment
Department of
Veterinary Science

Accelerating Medical Progress on Equine LamenessIn the horse world, lameness is a major problem.
On this point, everyone agrees. Whether yourfocus is elite equine athletes or pleasure horses,
whether you are a professional or a recreational
rider, whether your primary breed of interest islarge or small, musculoskeletal injuries are common and potentially very serious.
Substantial progress has been made over the last
several decades in areas of both lameness diagnosis
and treatment. Importantly, the future holds asmuch promise as ever. Science and technology arecontinuing to drive advances in clinical disciplines.
Cell biology is a good example. With next
generation sequencing applied on a genomic scale(inclusive of all DNA or all RNA), it is now possible to broadly compare gene expression between
individual tissues and cell types. Data-driven scientific approaches are discovering a large numberof genes that nobody realized were important. The
results are providing new insights into cellular
identity, normal function, and disease mechanisms
in areas that have direct relevance to lameness.
New understanding about individual cell types
enables diagnostic and therapeutic strategies tobe refined. Consider cartilage as an example.
Our bodies contain several different cartilaginous
tissues—joint (articular) cartilage, non-articular
structural cartilage, cartilage that is replaced bybone through a process called endochondral ossification, and others. Although all types of cartilage
have features in common, an understanding of theunique cellular characteristics that define articularchondrocytes is clearly an important parameter toconsider with joint diseases.

Going forward, veterinarians will increasingly
have access to molecular biomarker panels to help
refine their list of differential diagnoses, to selectoptimal therapies, and for patient monitoring. We
already hear about these approaches with cancer
patients, and the same concepts are applicable forbone, cartilage, tendon, ligament, and muscle tissues. The clinical goals include improved sensitivity
in monitoring health as well as early identificationof disease problems and how the patient is responding to treatment.
On a therapeutic level, cell-based approaches
are generating high levels of interest and for goodreasons. The term “stem cells” is mentioned frequently. Cells can be used therapeutically to deliver
beneficial equine-specific growth and differentiation factors to an area of injury, to modulate thepatient’s immune system in helpful ways, and insome cases to directly generate a repair tissue. Thereis much to learn and quite a bit of misinformation
being disseminated, but cell-based therapies do
indeed hold a lot of promise.
Finally, we have entered the era of medical
informatics. Hardware, software, and data storage
options in computer science have advanced rapidly
to enable “big data” analyses that resolve biomedical relationships and patterns from “-omic” andpopulation levels that would be very hard to appreciate by looking only at an individual gene ora single patient. By analogy, consider how difficult
it would be to resolve crop circles and other patterns in a grain field while standing on the ground.
They are much easier to appreciate while looking
out the window of an airplane. It is not an “either/or” issue—broad and targeted analyses are both
important and often complementary.
continued on page 6.