One of the most well-attended sessions at each year’s American Association of Equine Practitioners’ Convention is the Kester News Hour. During this event, a panel of veterinary experts presents the equine reproduction, medicine, and orthopedic studies from the past year that they found most important and impactful. This year’s panelists included Carrie Finno, DVM, PhD, DACVIM, of the University of California, Davis, School of Veterinary Medicine; Kyla Ortved, BSc, DVM, PhD, DACVS, of the University of Pennsylvania; Maria Schnobrich, VMD, DACT, of Rood & Riddle Equine Hospital; and Katie Seabaugh, DVM, DACVS, DACVSMR, of Colorado State University’s Equine Orthopaedic Research Center.
Here are three standout papers from the Medicine portion of the News Hour.
The Graying Gene’s Effect on Melanoma Incidence
Finno presented a paper investigating the speed of graying and melanoma incidence in gray horses—an equine population predisposed to this type of skin tumor. The researchers’ goal was to determine the role that copy number variations for the graying gene plays in the speed of graying and melanoma risk. They found that horses with only two copies of this gene will gray slowly and have a lower incidence of melanoma, while horses with three gene copies gray faster and have a higher melanoma risk. A horse with two copies of the graying gene bred to another with two copies is likely to produce a desirable dapple gray offspring.
Breeders can have genetic testing—the Gray Copy Number test at UC Davis Veterinary Genetics Laboratory—performed on sire and dam to determine a foal’s outcome.
Reference
Rubin, CJ., Hodge, M., Naboulsi, R. et al. An intronic copy number variation in Syntaxin 17determines speed of greying and melanoma incidence in Grey horses. Nat Commun 15, 7510 (2024).
EHV-1 Study and Survey Findings
Finno then presented results gleaned from a survey of ACVIM diplomats on the efficacy of equine herpesvirus-1 (EHV-1) vaccination. This information helps update the EHV-1 ACVIM Consensus Statement.
- Vaccination does not prevent EHV-1 infection, and while it causes minimal reduction in clinical disease, veterinarians still support its use.
- Pharmacologic treatment has minimal to no benefit except with valacyclovir if given in advance of EHV-1 exposure.
- Viremia occurs first before abortion or equine herpesvirus myeloencephalopathy (EHM), but there is little evidence that duration or degree of viremia correlate with abortion or EHM.
- Sampling is important for diagnostic measures. It is advisable to do both blood and nasal swabs when possible. With everyday sampling, there is no difference between blood or nasal swabs. Nasal swabs are preferred during outbreaks with large numbers of horses. For abortions, blood samples are most important.
Another study related to the EHV-1 and EHM 2021 outbreak in Valencia, Spain, researchers looked at horses’ long-term performance following ataxia and complications from EHM. Of 26 horses with severe EHM clinical signs, 68% returned to exercise and 53% returned to full performance. Milder ataxia is associated with a greater likelihood of full recovery. Horses with urinary or vascular complications were more likely to be euthanized.
Reference
de la Cuesta-Torrado M, Velloso Alvarez A, Neira-Egea P, Cuervo-Arango J. Long-term performance of show-jumping horses and relationship with severity of ataxia and complications associated with myeloencephalopathy caused by equine herpes virus-1. J Vet Intern Med. 2024 May-Jun;38(3):1799-1807. doi: 10.1111/jvim.17070.
Lyme Disease and Nuchal Bursitis
Ortved reported on a paper about Borrelia burgdorferi’s (Lyme disease bacteria) association with elevated outer surface protein A-specific (OspA) serum antibodies in horses in the Northeastern United States.
In this retrospective study, researchers evaluated 11 horses that had been euthanized due to nuchal bursitis and 19 live horses with nuchal bursitis. They compared them to 15 healthy, unvaccinated controls. Of 500 PCR samples submitted, Borrelia was detected in 35, and of the 35, only 30 had nuchal bursitis.
Nineteen horses were included in the study, with clinical signs of poll swelling, pain on palpation, reluctance to move the head, and drainage of the nuchal bursa. Thirteen infected horses received bursoscopy surgery, six were treated medically, and 15 received intrabursal injection with antimicrobials, hyaluronic acid, and corticosteroids. Across all the treatments, 16 of the 19 improved and nine returned to athletic work.
The nuchal bursa was the only synovial structure in which Borrelia was detected. High OspA titers were common in horses with chronic Borrelia infection in the nuchal bursa. The authors recommend targeted treatment for Borrelia, suggesting that surgery is the best approach. Despite treatment, horses might experience recurrent or persistent disease.
Reference
Pearson EK, Guarino C, Cercone M, Divers T, Lambert J, García-López J, Johnson AL, Engiles JB, Marconi R, Smith J, Brown K, Pinn-Woodcock T. Association of Borrelia burgdorferi with nuchal bursitis and elevated outer surface protein A-specific serum antibodies in horses of the northeastern United States. J Am Vet Med Assoc. 2024 Sep 6;262(11):1476-1484. doi: 10.2460/javma.24.05.0312
Related Reading
- Disease Du Jour: Nuchal Bursitis in Horses
- Disease Du Jour: Lyme Disease in Horses
- Is Vaccination Against Equine Herpesvirus Type 1 (EHV-1) a Rational Choice?
Stay in the know! Sign up for EquiManagement’s FREE weekly newsletters to get the latest equine research, disease alerts, and vet practice updates delivered straight to your inbox.
