GLUCK RESEARCH SPOTLIGHT
Our research laboratory is interested in understanding, treating and preventing equine infectious diseases. One of our primary interests is to better understand the genetic and antigenic diversity of equine rotavirus groups A and B. In addition, we hope to characterize and identify correlates of protective immunity against rotavirus infections in horses.
Mare and foal in green spring pasture.
Due to Equine rotavirus A’s incredibly infectious nature, high number of virus particles shed in fecal matter, and other factors, it is very hard to contain once an outbreak occurs.
© 2017 by Smerikal
Equine rotavirus A (ERVA) globally causes rotaviral diarrhea in foals and was first described in 1975. Two structural proteins, encoded by P and G genotypes, are recognized, of which G3, G14 and P[12] are the most common. Swift and intensive medical treatment typically prevents fatalities but represents a significant economic burden to the equine industry.
Due to ERVA’s incredibly infectious nature, the high number of virus particles shed in fecal matter, its environmental stability, and the non-enveloped structure, ERVA is very hard to contain once an outbreak occurs, which can lead to a heavy burden on farm staff and veterinarians. Therefore, prevention through biosecurity measures, monitoring programs and vaccination is of the utmost importance.
Before the introduction of the monovalent G3 vaccine by Zoetis in 1996, ERVA infection manifested as a disease of neonatal foals. Mares are vaccinated three times during pregnancy at 8, 9, and 10 months of gestation to generate a protective passive immunity to the foal through colostrum.
Interestingly, rotaviral diarrhea attributable to ERVA can be observed in foals between three and four months of age born to vaccinated mares and in neonates of unvaccinated dams.
Foals at younger ages are much more susceptible to infection and develop more severe clinical signs. With intensive treatment, rotaviral diarrhea has a high survival rate of 94%. However, without treatment, ERVA can be rapidly fatal, especially in neonates.
An ongoing collaborative research project at the University of Kentucky Gluck Equine Research Center is focused on whether vaccination against ERVA G3P[12] provides cross-protection against ERVA G14P[12], with an additional goal of monitoring the duration of maternally- derived protective antibodies.
Serum samples were collected from mares pre-vaccination, post-vaccination and for multiple months post- foaling. Foal serum samples were collected prior to nursing and bi-weekly for up to seven months post foaling.
Additionally, fecal swabs from both the foals and mares as well as colostrum and milk samples were collected.
A total of 50 mare-foal pairs were included in this study, leading to a total of more than 1,500 samples. A virus neutralization assay was used to determine neutralizing antibody titers in serum against ERVA G3P[12] and ERVA G14P[12].
Based on preliminary data, vaccination of mares maintained and increased ERVA G3P[12] virus neutralizing titers. Importantly, serum antibodies were cross- protective against ERVA G14P[12]. Further, ERVA G3P[12] and ERVA G14P[12] neutralizing antibodies are passively transferred through the colostrum as pre-nursing neutralizing antibodies were undetectable and increased greatly in post- nursing samples.
Lastly, we noted that titers of neutralizing antibodies in the foals decreased steadily after birth.
Work on this project is currently ongoing. Once serum virus neutralization assays are completed colostrum and milk samples will be tested using the same assay to determine the level of transfer of neutralizing antibodies from the dam to the colostrum and from the colostrum to the foal.
Furthermore, RT-qPCR of fecal swabs for ERVA G3P[12], G14[12] and ERVB will be performed to identify asymptomatic infections due to natural exposure during the project period. In future experiments, we hope to determine the precise antibody titer necessary for protection against ERVA beyond the meonatal period.
Article by Lianne Geertrui Eertink, PhD Student Gluck Equine Research Center Supervisors: Drs. Feng Li and Dan Wang - Press release by Equine Disease Quarterly