JANUARY 2024 VOLUME 33, NO.1

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 THIS ISSUE
INTERNATIONAL

Fourth Quarter 2023.....P. 2,3
Antimicrobial usage.....P. 3,4
Is vaccination against
Equine Herpesvirus
Type 1 (EHV-1) a
rational choice?............P. 5,6
KENTUCKY

Equine Rotavirus –a 2023 perspective.......P. 7
T H ANK YOU S PON SO RS!

R E SE A R C H SPOTLIGHT

An improved understanding of the
genome of Sarcocystis neurona, theprimary cause of EPM

Our lab is working to solve equine protozoal
myeloencephalitis (EPM), one of the mostcommonly diagnosed neurologic diseases inhorses in North and South America. Annual
direct costs associated with the diagnosis andtreatment of EPM represents a large economic
burden to the equine industry and is estimatedto be between $55.4 million and $110.8 million
in the United States alone. This does not accountfor the additional economic impact due to lost
production, decreased performance and the costof care during recovery. Even after successful
veterinary intervention, full recovery from thedisease can be difficult due to lasting damage totissues of the central nervous system.
EPM is caused primarily by Sarcocystis neurona,a single-celled parasite. Normally, Sarcocystis has
a two-host lifecycle where it spends most of its
time in small mammals such as skunks, racoons
and nine-banded armadillos. After asexual
replication, parasites will form dormant cysts(sarcocysts) in the muscle tissue of this animal,
which are later ingested through scavenging by
the opossum definitive host.

In the opossum, the parasites excyst in theintestines, where they sexually replicate toproduceenvironmentally-stable
infective
sporocysts that are passed along with feces
into the environment. Interestingly, the natural
lifecycle of S. neurona does not include thehorse. Horses become accidental hosts when
they ingest feed or water contaminated withopossum feces containing these sporocysts. In
the horse, the parasites excyst in the gut andmigrate to the brain and/or spinal cord where
they cause local inflammation and tissue damage.
Depending on the location of this inflammation,clinical signs can vary to include slightincoordination, asymmetric muscle atrophy,
partial facial paralysis, difficulty swallowing,
ataxia, recumbence, seizures and/or death.
Of 5,250 horses sampled in 2013 from 18 statesacross the United States, seroprevalence ofantibodies against S. neurona was 78% indicatingthat horses are commonly infected by thisparasite. A study by the National Animal Health
Monitoring System in 2001 reported the annual
occurrence of EPM to be approximately 0.14%
in the US, with case fatality rate at 4.7%. The
large discrepancy between the seroprevalence ofantibodies to S. neurona and the low occurrenceof EPM is puzzling and suggests that disease
pathogenesis is complex.

JANUARY 2024 | 1

INTERNATIONAL
Initially revolutionized by the sequencing of
the human genome, contemporary research now
permits efficient investigation of the proteome,transcriptome, microbiome, etc. of any organism
for which there is a high-quality genome
sequence and annotation (identification of thestructure and functional importance of individual
genes). Using the horse as an example, the equinereference genome has allowed for identificationof genetic variants associated with coat-color,dwarfism, cytokine expression and multiple othertraits. Furthermore, the equine reference genome
has made possible the Functional Annotationof Animal Genome (FAANG) project, acollaborative initiative promising to correlate andmake available a tissue-specific transcriptome(identification of all the genes expressed ina specific cell type) and regulome (all of theregulatory components of a specific cell type) of
the horse.
Like “omics” investigations in humans andhorses, computational approaches represent a
powerful toolset to improve our understandingof S. neurona and EPM. The current reference
genome for S. neurona was produced morethan a decade ago. Using state-of-the-art, nextgeneration sequencing technologies and improved
computational methodologies, we have generated
an updated reference genome for S. neurona thatprovides an improved assembly and more accurate
genome annotation. Importantly, previous geneannotation for the S. neurona genome reliedheavily on evidence from the “close” relatives
Toxoplasma gondii and Neospora caninum. In thisnew genome, the structure of each gene has been
painstakingly curated using evidence derived
specifically from S. neurona, which should ensure
the peculiarities caused by 250 million years ofSarcocystis evolution remain evident.
This collaboration between the University of
Kentucky’s Gluck Equine Research Center,
Purdue University and the University ofGeorgia will give us and other researchers abetter understanding of the genetic “language”
of S. neurona, which should lead to improved
diagnostic methodologies, preventative measuresand treatments for EPM.
Learn more about the authors by clicking
their names:
Jamie Kaj Norris, PhD Student
Dr. Dan K. Howe, Supervisor
Gluck Equine Research Center, University of
Kentucky.

2 | EQUINE DISEASE QUARTERLY

Fourth Quarter 2023

International report on equine infectious
diseases.
This report collates information provided bydiagnostic laboratories in Lexington, Kentucky,
University of Kentucky Veterinary Diagnostic
Laboratory and Equine Diagnostic Solutions,
Inc. (EDS). We are also grateful to IDEXX
laboratories, Germany, for sharing theirquarterly PCR respiratory panel results with thiscommunity.
We have further included information fromthe International Thoroughbred Breeders’Federation, the International Collating Centre(ICC) in Newmarket/Cambridge, United
Kingdom, and information from the American
Association of Equine Practitioners’ Equine
Disease Communication Center (EDCC). This
report summarizes heightened activity of several
relevant contagious or environment-linked
diseases among equids. We encourage everyone
to report laboratory-confirmed (toxico) infectious
disease of Equidae to the ICC or EDCC.
For North America and Europe, there is steadyreporting of Strep. equi spp. equi (Strangles)
cases. Several North American states andprovinces report single cases of EIA (exception:
Texas with eight), while there is a single ‘Old
World’ report from Bulgaria.
While the third quarter experienced a true surgeof West Nile virus (WNV) infections in California
and the U.S. Rocky Mountain states, the situation
has cooled a little. New cases have been reported
scattered across the U.S. and from the eastern
Canada provinces. The same holds for Easternequine encephalitis virus (EEEV) infections,which decreased during fall/winter due todecreased mosquito activity. The Mediterranean
Basin also reports WNV cases (28 from southern
Europe and two from northern Africa). Two more
endemic regions for WNV have emerged: Berlin
region, Germany, and Vienna, Austria.

EQUINE DISEASEQUARTERLYEDITORS
Lynne Cassone
Lutz Goehring
Allen Page
STAFF
Holly Wiemers
Hendri Smeenk

I N TE R N ATIO N A L
Combined, they report close to 10 cases of WNV
infections in horses. Interesting is the slow
spread of WNV cases into neighboring regions.
Noteworthy is the report of two Western equine
encephalitis (WEE) virus cases from a bordering
region between Uruguay and Argentina.
Incidental Equine Influenza cases/outbreaks
have been reported from Ontario, Tennessee
and the Pacific Northwest; a few more
reports reached us from Northern Europe.
Vesicular
Stomatitis
virus
(VSV
(Rhabdoviridae)) infections in horses in
the U.S. is still very present in California.
As Northern Hemisphere-bred broodmares enter
their third trimesters of pregnancies, the season
for EHV-1 (EHV-4) abortions has begun, and we
received reports of incidental abortions. Casesof EHV-1 neurologic disease (EHM) in North
America and Europe have also been reported.
Several countries in continental Europe reportoutbreaks of Atypical Myopathy (AM), the resultof Sycamore seeds and seedling ingestion, which
can trigger a severe and life-threatening form of
type-1 (oxidative) muscle myopathy. Outbreaksof AM follow a seasonal and severe weather
pattern during winter and spring.
Kentucky laboratories and the laboratory inGermany report high incidence of Strep. equi
spp equi and EHV-1 positive samples. EDS(Kentucky) reports a small number of Equine
Influenza positive samples with sample origin
from the Eastern United States.
Learn more about the authors by clicking
their names.
Lutz Goehring
Edward O. Olajide
Gluck Equine Research Center – Department of
Veterinary Science - University of Kentucky

Antimicrobial usage

The discovery, development, clinical use andintroduction of antimicrobials into human andveterinary medicine as well as food animal andplant production transformed the management of
infectious diseases in the 20th century. Critically,
antimicrobials significantly improved the qualityof human and animal life. Apart from the effective
treatment of bacterial and fungal infections,the effect of antimicrobials is also reflected inincreasing meat production yields that has helped
to feed an ever-growing human population. Now,
the availability and uses of antimicrobials aretaken for granted by all who were born after theSecond World War.
Sadly, the injudicious, widespread overusein human as well as veterinary medicine has
rapidly led to a precipitous decline in theireffectiveness because of rapidly spreading
antimicrobial resistance among pathogens. This
real and present threat is making antimicrobials
ineffective in controlling infectious diseases inhuman and animal patients. The United Nations
Environment Health Programme document,“Environmental Dimensions of Antimicrobial
Resistance,” quotes, “Antimicrobial resistance(AMR) is already a leading threat to global
health and risks adversely affecting theenvironmental sustainability of the planet.”
Equine infectious disease management is now
faced with adopting strategies to stop expectations
that antibiotics and antifungal medicines
should routinely be used indiscriminately forthe prophylaxis of infections that may or may
not occur as a consequence of viral infections,
surgical procedures or stallion and broodmare
management. The horse owning public andveterinarians can no longer expect or dispense
antimicrobials without evidence that an infection
is caused by organisms that are confirmed to besensitive to a specific antimicrobial treatment.
Clinical investigation and diagnostic proceduresmust be aided by the appropriate laboratory
investigations and antimicrobial sensitivity
testing. In practice, the dilemma is that thisapproach is slower than a rapidly progressing
infection. The judicious use of a broad-spectrum
antibiotic until microbial culture and sensitivity
results are available may then be considered as afirst treatment step.

Material published in the
Quarterly is not subject
to copyright. Permissionis therefore granted toreproduce articles, althoughacknowledgment of the source
and author is requested.
Maxwell H. Gluck
Equine Research Center
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
gluck.ca.uky.edu

JANUARY 2024 | 3

IN T E R N AT IONAL
The time limiting factors for the clinicianare, first, rapid access to clinical pathology
laboratory facilities, and, second, requesting theappropriate tests based on a horse’s or herd’s
clinical presentation and symptoms; laboratory
professionals often can help guide these requests.
Going forward, animal management andhusbandry must be based on best practicebiosecurity, stable and personal hygiene,
animal movement, vaccination strategies andunderstanding immune system responses. Rapid
recognition of developing infections is an
essential part of good horsemanship. This meansa return to more intense monitoring of individual
horses and herd behaviour patterns. As in the
pre-antimicrobial era, being more in tune tochanges in appetite, attitude and daily monitoringof rectal temperatures to help identify earlysigns of illness is necessary. Furthermore, when
dealing with both accidental and post-surgicalwounds, appropriate topical wound management
strategies limit the need for antibiotics. Most cuts
and abrasions don’t need “antibiotic cover.”Within the equine industry, broodmare and young
stock practices have been a major culprit for theindiscriminate and liberal use of large amountsof antibiotics. Critically, strategies to limit
antimicrobial use to confirmed cases of postbreeding bacterial endometritis in susceptible
mares rather than for general prophylaxis has
resulted in a welcome reduction in usage without
a discernible impact on per mare cycle conception
rates. Additionally, treating healthy newborn
foals with a course of prophylactic antibiotics
is not necessary and should be reserved foruse following the appropriate diagnostic
procedures for the treatment of the sick foal.
Likewise, the risk of developing respiratory
disease (“shipping fever”) during and following
transportation is not decreased by a course of“preventative” antibiotics. Rather, best practiceis to ensure that the horse is healthy prior totravel and closely monitored for a minimumof three days at its destination. The larger risk
is that horses treated inappropriately prior totravel will develop resistant strains of pathogens,narrowing the choice of antibiotics for effective
treatment when they are truly necessary.

4 | EQUINE DISEASE QUARTERLYNational and international veterinary associations
are implementing guidelines for the responsible
stewardship of antimicrobials in response to theUnited Nations’ One Health recommendations.
These include the British Equine Veterinary
Association’s “Protect Me Toolkit.” It encourages
veterinarians and their practices to implement
antimicrobial stewardship strategies.
The response to the programme has reduced
the use of antibiotics significantly without
detriment to the horses in the care of alarge general and referral equine practice in
Newmarket during the last 10 years. While
this progress in antibiotic stewardship by UKequine practices has been substantiated by arecent study highlighting both improvement aswell as deficiencies in its implementation, there
is still much room for improvement. Taking
responsibility for the implementation of antibiotic
stewardship policies requires continuous
critical monitoring of drug usage, behaviours
and trends as well as ongoing education ofveterinary professionals and their clients.
In order to protect our ability to manage
infectious disease in animals and humans now
and in the future, strict antimicrobial stewardshipis essential. This is our collective responsibility
for all involved in this very diverse global equine
industry.
Fred Barrelet, DipVMS (Bern), Dr.med.vet.
(Bern), MRCVS
Rossdales Ltd, Newmarket, UK
fred.barrelet@rossdales.com_______________________________________
Please visit our website for additional
information about our research projects.

Scan the QR code or click here_______________________________________

IN T E R N AT IO NAL
Is vaccination against Equine
Herpesvirus Type 1 (EHV-1) a rational
choice?
“Those who cannot remember the past arecondemned to repeat it.”George Santayana, The Life of Reason, 1905”
In the early 1930s, researchers in the Departmentof Animal Pathology at the Kentucky Agricultural
Experiment Station, namely Dimock, Edwards,
Doll and others, together with colleagues at
Vanderbilt University, Goodpasture and Randall,
performed groundbreaking research on an
equine abortion epidemic plaguing the industry.
They showed in a series of studies that thecausative agent was “filterable,” i.e., a virus,
which they propagated in various experimental
models, including infected tissue cultures takenfrom aborted fetuses, grafts on chorioallantoic
membranes of fertilized eggs and Syrian
hamsters. The specific cause, a herpesvirus,
however, was not confirmed until the 1960s.
Equine abortion virus, as EHV-1 was originallycalled, caused so much damage that vaccinationof horses was attempted before the final
identification of the virus. The early trials weredone with inactivated preparations after virus
amplification in hamsters but were controversial
because severe local and systemic reactions
ensued. What is more, they were not sufficiently
effective against abortion storms within the highdensity horse populations of Kentucky. Therefore,
live virus preparations were introduced soon
thereafter in controlled infection programs inmares. Finally, in the early- to mid-1960s, cell
culture adaptation and weakening of EHV-1
strains resulted in the development of modifiedlive virus (MLV) vaccines, some of which arestill in use. It was only in the late 1970s that theplanned infection programs were abandoned,
thanks to the demonstrable safety and efficacy,
albeit limited, of developed vaccines.
In the early 1960’s, two main types of EHV-1
vaccines were developed: inactivated (killed)
vaccines and MLVs. Bryans and Doll firstdescribed the use of inactivated Ky-D, grown inhamsters, for immunization of young horses. At
the same time, in Europe, Mayr and colleagues
developed an MLV by repeated passage of virus
in cultured cells. Interestingly, nothing much haschanged principally in the production of thesevaccines to this day.

While MLVs are thought to generally provide
stronger protection, they may not be suitablefor pregnant mares or immunocompromised
horses; inactivated vaccines are thought to offer asafer alternative for these sensitive groups.
The vaccination schedules for EHV-1 varies
depending on the horse’s age and the type of
vaccine used. Foals typically receive their initial
vaccination at 5 to 6 months old, followed bybooster vaccinations every six months until theyreach 2 years old. Adult horses require booster
vaccinations at least every six months to maintainsome level of immunity. In pregnant mares, theonly vaccine licensed “to aid in the protection
against EHV-1-induced abortion” is to be used
three times during pregnancy. In the absenceof a radically different approach to vaccine
formulations, vaccination habits and schedules
are unlikely to undergo a major change.
As old as the vaccines themselves is thecontroversy regarding the efficacy of vaccination
against this virus and its close relative, EHV4, which during their long co-evolution with
their natural host have excelled at the art ofimmune evasion. In other words, EHV-1, likeany other herpesvirus, does everything it can
to circumvent and trick the immune response.
This makes the development of new and more
efficacious vaccines inherently difficult. Whilecountless researchers have tried and failed, wemust acknowledge that we still (have to) rely on
products that are old but have yet to come of age.
It is, however, accepted by many that vaccination
against EHV-1 remains a critical component ofresponsible horse care and occurrence reduction of
the most devastating consequences of the infection,equine herpesvirus myeloencephelopathy (EHM)
and abortion.
We would like to think that, by incorporating
EHV-1 vaccines into a comprehensive preventive
health care plan, horse owners and veterinarians
can ensure the health and well-being of our equinecompanions. Although two recently publishedsystematic reviews and meta-analyses of vaccinesand vaccination regimes have revealed that
confidence in the value of vaccination is low,
it remains the consensus that vaccination is an
important tool for reducing EHV-1 spread and theseverity of clinical signs.

JANUARY 2024 | 5

INTERNATIONALKENTUCKY

One may argue that these analyses are worrying– and they indeed are. On the other hand, one
can refer to data that have shown a clear decrease
in EHV-1-induced abortions in areas where
vaccination is widely employed, for example inbroodmare farms in Kentucky. While the reduction
in cases is hardly the result of vaccination alone,
it remains part of a comprehensive approach tomaintain the (reproductive) health of operations.

Equine Rotavirus – a 2023 perspective

Considering these systematic analyses andfindings, one has to recommend continuation of
vaccination programs, although it would always
be better to have clear and convincing evidenceof vaccine and vaccination efficacy. It seems
likely we will have to continue to live with theuncertainty as we are, unfortunately, still far
away from the astounding efficacies of mRNA
vaccine technology, which has been used tocontrol COVID-19. We must be aware of the past
limitations of these vaccines and recognize thatvaccine development will continue to have anelement of trial and error and remain somewhat
unpredictable. However, it is clearly worthwhile
to continue the quest of finding a more reliablevaccine for EHV-1 and to explore new promisingtechnologies. We must ensure that studies to test
vaccines and vaccination regimes are informativeand properly done. If we are nimble, the hope will
stay alive that, one day, we will have irrefutableevidence that one vaccine or another will do what
vaccines are supposed to do: prevent clinicaldisease, and possibly even infection. It must
reman our goal to continue towards a solution thatputs owners and individuals at ease and instills
confidence that horses in our care are protectedagainst EHV-1 infection and its consequences.
Dr. Klaus Osterrieder
Professor of Virology and Chair
Institut für Virologie, Berlin
no.34@fu-berlin.de

6 | EQUINE DISEASE QUARTERLY

Since the discovery of equine rotavirus B (ERVB)
by the University of Kentucky Martin-Gatton
College of Food, Agriculture and Environment’s
Department of Veterinary Science in 2021, researchhas been ongoing to develop tools to protect
foals against infection. The equine industry has
answered the call for financial help, and, along withinternal funds from the university, a substantial
amount was raised to push forward on vaccine
development and antibody synthesis strategies.
Rotavirus is highly contagious with extrapolated
data suggesting that only 100’s to 1,000’s of
infectious virus particles are needed to infectsusceptible foals. This makes biosecurity achallenge. Measures that farms have employed
to break the cycle in an outbreak or prevent
infection include foaling outside with personnel
wearing personal protective equipment, minimal
handling of the foal for the first week of life otherthan the customary ‘foal exam’ at 12-24 hours ofage and rigorous observance of staff/traffic/horse
movement in the foaling barn. Links to additional
resources are included below. Control of infection
during an outbreak is a considerable challenge,emphasizing the need for a protective vaccine.
One significant hurdle in the development of
ERVB-directed treatment and prevention tools
is the inability to grow the virus in a laboratory.
The currently available equine rotavirus A(ERVA) G3[P12] vaccine was developed froma cell-adapted strain of ERVA. This vaccine has
made neonatal ERVA extremely rare when foals
are born to appropriately vaccinated mares.
The reason why ERVB replicates robustly infoals but has not been able to be grown in thelaboratory remains elusive. This is currently
under extensive investigation at the Li-Wang
Lab at UK’s Gluck Equine Research Center. The
importance of cell-specific surface molecularpatterns in pathogen and cancer biology researchhas been increasingly demonstrated. Recent
work on specific cell surface markers recognizedby different rotaviruses has demonstrated that
ERVA and ERVB recognize different cell surface
markers with varying affinity. While ERVB
does not recognize or interact with the same cellsurface glycoproteins as ERVA, promising work
has identified molecular elements of cell surface
markers for which ERVB has a higher affinity.

K E N T U C KY
These affinities for specific cell surface markers
may be used as a screening tool to identify
additional cell line candidates in which ERVB
could be propagated in the laboratory going
forward.
While ERVB cannot yet be grown in thelaboratory, vaccine technology has significantly
improved since the first equine rotavirus vaccine
was developed in the early 1990s. As a result, theneed to grow ERVB in the laboratory to generatea vaccine is no longer the insurmountable barrier
it once was and several alternative vaccine
platforms are currently being explored. Indeed,
COVID-19 catapulted vaccine development
forward by decades and veterinary medicine is
now benefiting from that technology. Vaccine
platforms, such as the insect virus baculovirus, canbe used as a means to deliver specific components
to elicit an immune response, while also being
safe for the animals that receive it. Other vaccine
technologies, such as mRNA, virus-like particles
and expressed protein antigens also show hugepromise for the veterinary field. In addition
to new antigen formats, the addition of lipidbased nanoparticle adjuvants has improved theeffectiveness of modern vaccines considerablycompared to older products.

These adjuvants are changing the landscape of
vaccine development, which may ultimately
result in lower antigenic loads (lower quantitiesof viral components) per vaccine and longer
intervals between vaccinations.
Currently, the University of Kentucky is testing
the immunogenicity and safety of four ERVB
vaccine candidates; results of these studies will
be made available as soon as possible. Given that
ERVB was only recognized three years ago, theprogress that has been achieved in this relatively
short period of time is remarkable and emphasizes
the importance of cooperative efforts between
the Gluck Equine Research Center and theequine industry in addressing industry problems.
Learn more about the authors by clicking theirnames.
Dr. Emma Adam
Dr. Feng Li
Dr. Dan Wang
Gluck Equine Research Center
University of Kentucky

These two videos are additional
information to this article and byclicking on the images you will
be able to watch them on YouTube.

JANUARY 2024 | 7