APRIL 2022 VOLUME 31, NO. 2

A PUBLICATION BY THE UNIVERSITY OF KENTUCKY DEPARTMENT OF VETERINARY SCIENCE, MAXWELL H. GLUCK EQUINE RESEARCH CENTER
FUNDED BY:

EQUUS / STANDARDBRED STATION, INC.
M&J INSURANCEIN T HIS IS S U E
INTERNATIONAL, PG. 2
Equine Infectious Diseases
Fourth Quarter 2021
NATIONAL, PG. 3
Hydrops Allantois andHydrops Amnion in
the MareKENTUCKY, PG. 4-7
Biosecurity on Equine
Breeding Farms
Equine Amyloidosis
Equine Leptospiral
Abortion in Central KY

TH A N K YO U
SPON SO RS

C O MME N TARYAdvances in Understanding of the Pathophysiologyof Placental Disease
One of the greatest joys in the horse-breeding industry
is the birth of a strong, healthy foal. As such, theircaretakers will go to whatever means necessary
to ensure a good outcome, including painstaking
monitoring for signs of a problem such as early udder
development or vaginal discharge. Despite their hard
work, some mares still abort seemingly out of the blue,
or give birth to a “peanut,” a small, runty foal which
struggles to gain weight and thrive. Unfortunately,
any number of diseases or conditions can cause theseoutcomes, and it often feels like there is nothing we cando to prevent them.
Fortunately, there have been massive developments
in research techniques recently that allow researchers
to understand the underlying mechanisms of disease.
These range from genetic analyses to RNA-sequencing
and advanced proteomics and lipidomics. In brief,
DNA is transcribed into messenger RNA (mRNA),
which can be translated into protein. Specific proteins(enzymes) alter the use and form of lipids, and eachhas a slightly different role in our understanding ofhealth and disease. Together, these techniques use theinterconnected systems of genetic material and proteinsto provide a more holistic understanding of normal andabnormal pregnancy and can be used to identify betterways to diagnose, treat, and even prevent pregnancy
complications.
Genetic analysis provides information about a horse’s
specific DNA. This remains the same throughout ahorse’s life and can be passed directly to their offspring.
Perhaps the best-known genetic testing in horses is
the 5-panel test in Quarter Horses, which includes
tests for hyperkalemic periodic paralysis (HYPP),
hereditary equine regional dermal asthenia (HERDA),
polysaccharide storage myopathy (PSSM), and others.
If a breeder knows that their mare has one copy of anyof these genes, they can avoid complications in theirfoals if they make sure they breed to a “clean” stallion,
or one who does not have a copy of that gene, whichmakes our horses healthier overall. Additionally, there
is work being done to identify the genetic basis forumbilical cord torsion, placentitis, red bag delivery,
and others.
RNA-sequencing analyses can assess the amount ofmRNA produced in a tissue during disease. Because
mRNA expression is the first thing to change during
disease, we can often see the body’s immediate
response to an infectious agent, as well as how thatagent causes the body’s response to change over time.
Additionally, mRNA is relatively simple to measure,allowing us to monitor expression of over 32,000 genes.
By monitoring this response, we can better understandwhat treatments are likely to help, what biomarkers
may allow better diagnosis, and how to help preventthe horse from getting sick in the first place.
Lastly, proteins and lipids do the heavy lifting in tissues
and are what exert the majority of the biological effects
we see. Unfortunately, the technology we have inplace for testing large numbers of proteins and lipids
is expensive and clumsy, making it difficult to look atchanges which are happening at a cellular level. Evenso, proteins and lipids are often the best biomarkers
because they remain in circulation for relatively long
periods of time and reflect actual physiological changes
happening in response to the disease. For example,
proteomic studies have identified biomarkers forplacentitis that change in blood and in amniotic fluid.
From the outside, many of these molecular techniques
seem pedantic and far removed from clinical reality;
however, these techniques are what allow researchers tobetter understand the underpinnings of disease and how
to diagnose and treat it. RNA-sequencing has recently
been used to identify how the mare and unborn foal act
to fight both ascending and nocardioform placentitis,
including how these diseases affect blood vessel
development, nutrient transportation and immune
signaling. There have been other studies which haveidentified the key changes occurring in the placenta
during early pregnancy – this work could ultimately
lead to improved pregnancy diagnostic tests and betterways to assess pregnancy health.

APRIL 2022 | 1

These molecular level analyses provide keen insight
into the workings of the placenta, and how thosefunctions are disrupted during disease. This issue of
the Equine Disease Quarterly contains articles by Dr.
Von Dollen on hydrops and Dr. Swan on leptospiralabortion. Researchers are using various molecularanalyses to better understand the pathophysiology ofboth of these important causes of fetal loss. Although
it can be difficult to see exactly how this knowledge
benefits horses today, the information from thesestudies is what will allow researchers to develop better
techniques for diagnosis, treatment and prevention of
disease. The broad view these techniques offer allows

a more complete picture than any previous technology,
and is already making a difference in how we diagnose
and treat disease. Ultimately, these techniques makemajor strides towards every breeder’s goal of creating
pregnancies which result in strong, healthy foals.
CONTACT:
Shavahn Loux, PhD
shavahn.loux@uky.edu
Department of Veterinary Science
Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

I N T E R N AT I ONAL
Fourth Quarter 2021
International Report on equine infectious diseases

EQUINE DISEASEQUARTERLYEDITORS
Alan Loynachan
Rebecca Ruby
Lutz Goehring
STAFF
Tawana Brown
Holly Wiemers
Anita Hatchet

EDQ@uky.edu

The following data was primarily provided by theInternational Thoroughbred Breeders Federation;
International Collating Centre in Newmarket, United
Kingdom (UK); the Equine Disease Communication
Center of the American Association of Equine
Practitioners, and other sources. This report isretrospective and does not claim to be complete.
However, it provides an indication of heightened
activity of contagious or environment-related diseases
among equids. Reports of equine infectious diseases
were not received from Central and South America,
sub-Saharan and equatorial Africa, and from most partsof Asia (with Japan being an exception).

only had fevers and respiratory signs. EHM outbreaks
were also reported from central Europe and from theMediterranean basin (Italy).

Strangles was reported from various regions of North
America and Europe, including the British Isles.

Miscellaneous:
Approximately 20 laboratory submissions tested
positive for Taylorella equigenitalis in the UK. One
sample was PCR positive for equine coronavirus inAustria. Five submissions were PCR positive for
Lawsonia intracellularis in the UK. Three abortions
were attributed to Leptospira spp. (two in Canada andone in Japan), and two aqueous fluid samples from
central Europe tested PCR positive for Leptospira sp.
One horse tested positive for Potomac horse fever(Neorickettsia risticii) in the West region of the USA.
Ukraine reported a single equine case of anthrax.
The southern part of Africa reported a case of equine
encephalosis and several cases of piroplasmosis; nocases of African horse sickness were reported during
this quarter. Australia reported a case of Hendra virus
infection in a single horse.

Several influenza outbreaks were reported from regionsof North America, and from various parts of Europe,
mainly UK, France, and Germany. EHV-4 respiratory
disease was detected in groups of weanlings in
Kentucky, USA, as well as from isolated cases, mostly
from young stock, in North America, Europe (British
Isles, central Europe, and the Mediterranean basin),and the Republic of South Africa.
Individual cases of EHV-1 abortion were reported
from the Midwest region of the United States ofAmerica (USA), British Isles, continental Europe andfrom Japan. As expected with the cooler season in thenorthern hemisphere, outbreaks of equid herpesvirusassociated myeloencephalopathy (EHM) were reported
from several regions of North America (Eastern Canada
and the Mid-Atlantic, Midwest, and West regions of
the USA). EHM was typically detected in one or morehorses, while several other in-contact animals

2 | EQUINE DISEASE QUARTERLYWith the end of ‘mosquito season’ in the northernhemisphere, there were few cases of West Nile virus
encephalitis in North America (30-50 cases), andfew cases in Europe; three cases from central Europe(Germany), one horse from the Balkan region, and11 reports from countries around the Mediterranean
Sea. Eastern equine encephalitis virus infection was
detected in 15 horses this quarter, including states in the
Midwest region of the USA (Michigan and Wisconsin).

CONTACT:
Lutz Goehring, DVM, MS, PhD, Dip. ACVIM/ECEIM
l.goehring@uky.edu
Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

N ATIO N A L
Hydrops Allantois and Hydrops Amnion in the
Mare
While rare, dropsical conditions in the mare are aremarkably unfortunate gestational complication.
Hydrallantois (or hydrops allantois) and hydramnion (orhydrops amnion) refer to the pathologic accumulationof excessive fetal fluid within the allantoic oramniotic compartments of the placenta, respectively.
A mare affected by hydrallantois or hydramnion will
typically present after six months of gestation with arelatively rapid (on the order of days to weeks) onset
of increased abdominal size. Normal fluid volume in
the allantoic cavity at term is approximately 10-15 L,
while in cases of hydrops allantois, this can increase
to well over 100 L. For amniotic fluid, the normal
volume is approximately 3-5 L at term, with volumes
exceeding 50 L reported in some cases of hydramnion.
Hydrallantois is more common in the mare thanhydramnion, but diagnosis and management are largely
similar between the two conditions. A diagnosis relies
upon clinical history, physical examination, transrectal
palpation, and transabdominal ultrasound. Palpation
per rectum classically reveals a domed, fluid-filled
uterus, with the fetus unable to be palpated. When theuterus is evaluated by transabdominal ultrasound, alarge volume of fluid dominates the field of view (>20
cm in depth), with the fetus suspended within this fluid.
In some cases, the fetus cannot be visualized due to theextreme volume of fluid.
There are isolated case reports of delivery of a viable
foal, if the hydrops condition develops in late gestation.
However, the most common outcome is induced
abortion of a nonviable or deceased fetus, in order tosalvage the mare. Mares affected by hydrallantois or
hydramnion are at increased risk for the development of
prepubic tendon rupture, body wall herniation, uterine
rupture, and hypovolemic shock during abortion/
parturition. Due to these risks and the poor prognosis
for fetal viability, management of hydrops conditions
is generally accomplished through controlled drainage

of fetal fluids and fetal extraction with concurrent
supportive care of the mare. The client and clinician
should anticipate that the mare will likely retain her
placenta.
The underlying factors, which cause hydrops conditionsin the mare are not precisely known, but recent research
has identified significant differences in expression ofgenes influencing vascular development in normal
placentas versus placentas from mares affectedby hydrops conditions. The fetuses from hydrops
cases often display gross congenital abnormalities,
which have been hypothesized to contribute to thedevelopment of the condition through altered fluid
dynamics in the fetus (e.g., swallowing and umbilical
blood flow). Zoonotic Leptospira bacteria have been
isolated from the fetus and placenta of a small numberof hydrops cases. Therefore, personal protective
equipment is recommended to be donned when working
with hydrops cases. Recurrence of hydrops conditions
in subsequent pregnancies is not a recognized risk. In
one retrospective analysis of thirty cases of hydrops
at a referral hospital, 95% of affected mares produced
a normal foal in their subsequent pregnancy. Despite
the poor prognosis for fetal survivability, hydrallantois
and hydramnion are associated with a good prognosis
for a mare’s future broodmare career, if intervention
is sought early. Potential heritability of hydrops is asubject of slight controversy, with differing reports
found in the literature. A definitive study to answer
this question would be ambitious to achieve, given therarity of hydrops occurrence.
CONTACT:
Karen Von Dollen, DVM, MS, DACT
kvondollen@hagyard.com
Hagyard Equine Medical Institute
Lexington, Kentucky

Material published in the
Quarterly is not subject
to copyright. Permissionis therefore granted toreproduce articles, althoughacknowledgment of the source
and author is requested.

KEN TU CKY
Biosecurity on Equine Breeding Farms: Lessons
Learned from Rotavirus B
During the 2021 foaling season in central Kentucky,
area farms experienced an outbreak of neonatal foal
diarrhea. A novel equine rotavirus group B pathogen
was implicated in the disease based on compelling
genetic sequencing evidence coupled with the clinicalscenario of a highly contagious pathogen that causes
diarrhea in foals under 4 days of age. A PCR test forthe pathogen was quickly developed at the Universityof Kentucky, and testing information was shared withlabs in the US, England, Ireland, France, Argentina andJapan. Unfortunately, the development of an efficacious

vaccine has lagged behind, and disease control has
focused on prevention through the implementation ofincreased biosecurity protocols.
Obtainment of a correct diagnosis must never be
underestimated, but this can be hard to comprehend
when there are no available cures or protective
vaccines. However, a confirmed diagnosis is vitalin order to guide mitigation strategies, promote for
vaccine development, and leverage for increased
biosecurity measures and compliance.

Maxwell H. Gluck
Equine Research Center
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
gluck.ca.uky.edu

APRIL 2022 | 3

Workflow, management culture, and practices should
be adapted to meet the needs of a particular location.
Over and above determining the correct cleaning
process, disinfectant choice, application technique, andprotective equipment is the process of understanding
how a farm and its crew work, not only physically but
as a team. Biosecurity is as much about leadership as
it is about the actual protocol itself. Time and again
we see the heartbreaking results of a farm crew worn
down by long hours tending sick animals and adhering
to a protocol, only to find one member of the team whodoes not “buy in.” One breakdown in that team can beruinous to the control of an outbreak and disastrous formorale.
Farm visits are a challenge in the face of an outbreak as
we limit vehicular and foot traffic in vulnerable areas,such as the foaling barn. However, it is on these visits
where observing how people interact with each otherand their charges can be the key to success.
Development of a biosecurity protocol is a team effort
where all members contribute thoughts on how tomake a workable plan. This can be very hard to do,and suggestions from a third-party observer can often
be beneficial. Observers can help identify an optimal
starting point to help get everyone on the same gameplan and communicate the practicalities of a successful
biosecurity plan. Division of a workforce into units tocare for groups of geographically isolated horses can bea helpful component of the plan.
Some practical tips for increasing biosecurity include
wearing gloves, using disposable footwear and footbaths with appropriate disinfectant, practicing goodhygiene between stalls, which includes changing
gloves, washing hands and being free of organic
material, and limiting visitors.
Disinfectants will not work in the face of organic
material (e.g. feces, dirt, bedding). By simply removing
organic material, the pathogen load can be decreased by
up to 90%. Stalls and floors typically require scrubbing
with a detergent prior to application of a disinfectant.
Similarly, foot baths with disinfectant will only workwhen they are clean and changed regularly.
Items used in multiple stalls should be discouraged,
but at a minimum they should be disinfected between
animals and at the end of the day. All movements inthe barn should proceed from clean to dirty, and foals
showing signs of diarrhea should receive extra carein biosecurity. Aerosolization of infectious particles
may occur with pressure washing or with the use ofleaf blowers, so these practices should be avoided if
there are animals in the barn or if the stall is expected
to be occupied shortly after cleaning. Rotaviruses
may survive up to nine months in the environment
and therefore farms should not spread contaminatedbedding or manure onto their pastures.
The goal of any biosecurity program is to reduce theexposure of animals to disease, requiring a multifaceted

4 | EQUINE DISEASE QUARTERLY

A rotavirus group B infected foal with diarrhea.
Photo Courtesy of Dr Laurie Metcalfe, Rood andRiddle Equine Hospital.
approach and collaboration between farm personnel,
visitors, and veterinarians. All farms should have basic
biosecurity practices in place each foal season and aplan to rapidly increase biosecurity in the event of an
infectious disease event. Until an efficacious vaccine isavailable for rotavirus group B, farms will continue torely heavily on biosecurity practices to slow the spreadof this highly contagious disease.
CONTACT:
Emma Adam, DVM, PhD, DACVIM, DACVS
emma.adam@uky.edu(859) 257-4757
Department of Veterinary Science
Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

Equine Amyloidosis
Amyloidosis is a rare disease in which abnormal
protein, known as amyloid, is deposited within tissueand disrupts normal organ function. Multiple typesof amyloidosis occur in humans and domesticatedanimals, but only reactive systemic amyloidosis(AA) and immunoglobulin-derived amyloidosis (AL)have been described in horses. Reactive systemic
amyloidosis develops secondarily to chronic andnon-specific antigenic stimulation. Immunoglobulinderived amyloidosis occurs due to immunoglobulin
light chain deposition during plasma cell dysfunction.
Both AA and AL amyloid can be deposited systemicallyin multiple tissues or locally within a single organ.
The University of Kentucky Veterinary Diagnostic
Laboratory (UKVDL) USALIMS database wassearched for cases of amyloidosis to better understandthis disease in horses.
Eleven cases of amyloidosis were diagnosed at
the UKVDL from 2010 to 2021. Seven cases werediagnosed in horses that died or were humanely
euthanized, and four cases were diagnosed in surgicalbiopsy submissions. Five cases were identified inThoroughbreds, two in mixed breeds, and individual
cases in a Tennessee walking horse, Saddlebred,
Quarter horse, and warmblood. Horses ranged in age
from less than a year up to 16 years. Six cases werediagnosed in mares, four in geldings, and one in a colt.
Animals that were submitted for postmortem
examination presented with clinical histories of being
found dead (two cases), acute colic (three cases),chronic unresolving abdominal abscessation (onecase), or proliferative bone lesions (hypertrophic
osteopathy; one case). Amyloid was microscopically
identified in multiple tissues (systemic distribution) inall seven horses that died or were euthanized. Amyloid
was deposited in the liver and spleen (three cases);
liver, spleen, and kidney (two cases); liver, spleen,
and lymph node (one case); and liver and kidney (onecase). Four cases with liver involvement resulted inhepatic rupture and hemoperitoneum; two of these diednaturally and one was euthanized. Co-morbidities inthese horses included nodular pulmonary fibrosis, aortic
mineralization and aneurysm, chronic peritonitis, bonedisease (osteopathy), abdominal R. equi abscessation,mesenteric rent with small intestinal entrapment,
and chronic lymphangitis (big leg). Of note: Chronic
lymphangitis was evident in three of the seven necropsy
cases and was the only co-morbidity identified in morethan one animal. A chronic inflammatory condition was
not overtly identified in one case; this horse died due
to a mesenteric rent with small intestinal entrapment.

decreased athletic performance. Examination of thenasal mucosa can reveal nodular to diffuse thickeningof the nasal mucosa due to amyloid deposition.
Surgical excision is the treatment of choice for nasal
amyloidosis. Horses with cutaneous amyloidosis
commonly develop multiple papules, nodules, or
plaques in the skin of the head, neck, shoulders, andpectoral regions. Skin lesions are firm, non-painful, anddo not itch. There are no proven effective treatments for
cutaneous amyloidosis. Cutaneous and nasal forms are
not typically seen with the systemic form and do notdevelop from chronic inflammation, like the systemic
form. A surgical biopsy should be considered if nasal
or cutaneous amyloidosis is suspected.
Microscopically, amyloid from all cases consisted ofextracellular homogenous eosinophilic material that
distorted tissues. The material had an apple-green
appearance under polarized light, consistent withamyloid. Granulomatous inflammation was associatedwith the amyloid in the cutaneous and nasal forms. Noneof the cases were assessed by proteomic techniques,
electron microscopy, or immunohistochemistry.
In summary, equine amyloidosis is an uncommon causeof systemic, cutaneous, and nasal disease. Any horse
breed, sex, or age can be affected. The systemic form
is associated with chronic disease processes, and theliver, spleen, kidney, and lymph nodes are frequently
affected. Nasal and cutaneous forms are not associatedwith other ongoing diseases and have a good clinicalprognosis.
CONTACT:
Alan T. Loynachan, DVM, PhD, Dip. ACVP
alan.loynachan@uky.edu
Veterinary Diagnostic Laboratory
University of Kentucky
Lexington, Kentucky

Four cases of amyloidosis were diagnosed fromsurgical biopsy submissions. These included threecases of nasal (nasopharyngeal) amyloidosis and one
case of cutaneous (skin) amyloidosis. Horses withnasal amyloidosis typically present with clinical signsof epistaxis (nose bleed), difficulty breathing, or

APRIL 2022 | 5

Equine Leptospiral Abortion in Central Kentucky
Leptospires are zoonotic bacteria of worldwide
distribution. Adult horses acutely infected with
Leptospira develop clinical signs associated withacute liver and kidney failure. Additionally, a strong
association has been identified with equine recurrent
uveitis and leptospiral infection. In general, clinicalsigns of infection coincide with the bacteria’s natural
tropism to target and replicate within the bile tract,kidneys, blood, placenta, and eyes. Animals are mostcommonly infected through contact with water or soilthat has been contaminated with urine from an infected
carrier animal, either through drinking a contaminatedsource or through open wounds. Leptospires can persist
in the environment for weeks to months post exposure,which makes disease prevention and environmental
control difficult. Infection of pregnant mares can resultin abortion, stillbirth, or birth of a weak foal.
Since 2009, the University of Kentucky Veterinary
Diagnostic Laboratory (UKVDL) has diagnosed 122
cases of equine leptospirosis in fetuses or neonates.
This represents roughly 1.8% of the total numberof fetal cases submitted to the UKVDL during thistime period. On average, the UKVDL diagnoses ninecases of leptospiral abortion a year, but yearly cases
can range from one to 17. An increased incidence of
leptospiral abortion can occur in years with heavy
rainfall in the late summer and fall. Therefore, theincidence of leptospiral abortion and nocardioform
placentitis can be inversely related. Of the 122 cases,
80% were diagnosed in Thoroughbreds and 6.5% werediagnosed in Standardbreds, which directly mirrors thebreed distribution in central Kentucky.
Leptospirosis commonly causes abortions during mid

to late fetal gestation. Submissions to the UKVDL
ranged in gestational age from 5 to 11 months, withan average gestational age of 8.59 months. Grossly,
fetal and placental lesions can vary. When present, themost common gross lesions associated with abortion
are icterus, an enlarged mottled yellow liver, petechialhemorrhages within the placenta and/or fetal mucous

6 | EQUINE DISEASE QUARTERLY

membranes, and placentitis. Microscopic lesions include
placentitis, hepatitis, and nephritis. The organism istypically visible within the fetal and placental tissues
using a silver stain or immunohistochemistry.
Leptospira is a large genus of bacterial organisms ofwhich Leptospira interrogans is the most importantin humans and animals. Leptospira interrogans
has multiple serovars and specific serovars morecommonly cause clinical disease in different
domesticated animal. In horses, the serovars thathave been reported to cause abortion are Pomona,
Grippotyphosa, Icterohaemorrhagiae, Kenewicki, andBratslava. Currently, Pomona is the most frequent

serovar associated with abortion in Kentucky.
At the UKVDL, a combination of diagnostic tests is used
to aid in the diagnosis of leptospiral abortion. Currently,
the two most commonly utilized tests by UKVDL
veterinary pathologists are the microagglutination
test (MAT) and real-time polymerase chain reaction(q-PCR) assay. MAT testing is commonly performedon fetal heart blood or pericardial fluid and yields atiter indicating the fetus was exposed to leptospires
during gestation. MAT is a highly sensitive test withrelatively low specificity. In adult animals sequential
MAT titers are utilized and a greater than fourfold
increase in serial titers indicates recent infection in an
unvaccinated animal. In fetal tissues, any MAT titer isconsidered significant. Of the 122 cases, 96.7% of thecases had a positive MAT titer and 90.4% of these cases
had a positive MAT titer for either serovars Pomona
or Grippotyphosa. Fetal titers ranged from 1:200 to
1:204,800 with the most frequent titer being 1:6,400.
Most commonly, MAT titer results will be confirmedwith either histologic lesions and a qPCR test. In
2012, the UKVDL implemented a qPCR assay forthe detection of leptospires. PCR is a highly sensitiveand specific diagnostic assay in which a positive result
indicates the presence of the bacterial DNA within
the sample. Of the 122 fetal abortions, 44 of thesecases were qPCR tested and 95% of these cases tested
positive via PCR analysis.
In conclusion, leptospiral abortions represent animportant cause of equine abortion in central Kentucky.
Cases of leptospiral abortion are detected each year andfarm personnel should be aware that the aborted fetal
tissues and mare urine are infectious to other horses
and pose a health risk to people coming in contact withthem.
CONTACT:
Melissa Swan DVM, MS, Dipl. ACVP
Melissa.swan@uky.edu(859) 257-6917
Veterinary Diagnostic Laboratory
University of Kentucky
Lexington, Kentucky

Figure 3. Numerous leptospires are located within the placental stroma.
Leptospires are black and have a corkscrew to whip shape.

APRIL 2022 | 7