Immunization of Foals with Equine Rotavirus A Vaccine Can Stabilize or Increase Rotavirus-Specific Neutralizing Antibody Titers.

Overview

• This study investigated whether vaccinating young foals with an equine rotavirus A (ERVA) vaccine can boost or maintain their levels of neutralizing antibodies against the virus, potentially improving their protection against this common cause of foal diarrhea.

Background

• Equine rotavirus A (ERVA) is a leading cause of diarrhea in foals in the United States.
• A monovalent G3P[12] (‘G3’) equine rotavirus vaccine is available and commonly used.
• Previous studies have shown that maternal antibodies (neutralizing antibodies or NAbs passed from mare to foal) are often very high in young foals, which can interfere with the effectiveness of early vaccination around 30 to 45 days of age.
• The goal was to determine if vaccinating foals before they become vulnerable to ERVA infection can increase their neutralizing antibody levels despite the presence of maternal antibodies.

Study Design

• A total of nine foals were included in the study, along with two control foals.
• Two foals were vaccinated only once at three months of age with the commercial G3 vaccine.
• Seven foals received two doses: one at two months and another at three months of age.
• Two control foals were given a saline buffer (placebo) instead of the vaccine.
• The foals’ dams (mothers) were not vaccinated during pregnancy, ensuring that the foals’ maternal antibody levels were not artificially influenced by recent vaccination.

Measurements and Testing

• Neutralizing antibody (NAb) titers against both the G3 strain and a G14P[12] (‘G14’) strain of ERVA were measured before and after vaccination.
• Prior to vaccination, all foals had NAb titers of 256 or lower against both viral strains.
• NAb titers were assessed to determine the foals’ immune response to vaccination.

Results

• Following vaccination, NAb titers increased significantly in vaccinated foals:
• Up to 1024 against the G3 virus.
• Up to 512 against the G14 virus.
• The neutralizing antibody titers in vaccinated foals either stabilized or increased over time, depending on their pre-vaccination antibody levels.
• In contrast, unvaccinated control foals showed a rapid decline in neutralizing antibody titers with time.

Conclusions and Implications

• Vaccinating foals at two and three months of age can boost or maintain their rotavirus-specific neutralizing antibody levels despite the presence of maternal antibodies.
• This approach could provide better protection to foals before they become vulnerable to rotavirus infection, which typically causes diarrhea.
• Timing of vaccination is important—vaccinating too early may be ineffective due to interference by maternal antibodies, but vaccinating at two to three months shows promise.
• Overall, this study supports the use of the existing commercial monovalent G3 equine rotavirus A vaccine in young foals to enhance their immunity.