Rotavirus, a non-enveloped RNA virus, is a major infectious cause of foal diarrhea and has been documented to cause 50% or more of foal diarrhea cases in some areas.
While rotavirus diarrhea morbidity can be high (50% of susceptible foals), mortality is low (<1%) with veterinary intervention.
Equine rotavirus is transmitted via the fecal-oral route and damages the small intestinal villi resulting in cellular destruction, maldigestion, malabsorption, and diarrhea.
As many as 70% of all foals in the United States will have at least one diarrheal episode prior to weaning. Mare owners need to be aware that strict biosecurity and disinfection during the foaling season also mitigates the morbidity associated with most types of infectious foal diarrhea and other contagious diseases.
Vaccination of mares results in a significant increase in foals’ rotavirus antibody titers. Field trials of rotavirus vaccination in pregnant mares have shown a decrease in incidence and severity of foal diarrhea on farms that historically had annual rotaviral diarrhea cases. Other studies have shown increased rotavirus antibody in vaccinated mares’ colostrum.
The only available vaccine is conditionally licensed, contains inactivated rotavirus Group A, and is indicated for administration to pregnant mares to enhance concentrations of colostral immunoglobulins against equine rotavirus (Group A). The vaccine has been used in mares since 1996 in the USA and is considered to be safe.
Pregnant mares (regardless of vaccination history): Should receive a 3 dose series of intramuscular vaccinations at 8, 9, 10 months of gestation.
Concentrated horse breeding areas in the US routinely use rotavirus vaccine in pregnant mares. Pregnant mares that will be shipped to regions that have had a history of rotaviral diarrhea should also be considered candidates for vaccination.
**It is essential that the newborn foal receives an adequate amount of colostrum and absorbs sufficient anti-rotavirus antibodies from rotavirus-vaccinated mares.
Newborn foals: There are no data to suggest that vaccination of the newborn foal with inactivated rotavirus A vaccine has any benefit for preventing or reducing the severity of infection.
As colostral-derived antibody titers wane at approximately 8 weeks of age, foals may develop rotaviral diarrhea. However, the severity of diarrhea is generally milder and of shorter duration than in foals that become ill within the first 4 weeks of life.
Other adult horses: Vaccination is unnecessary