Prevention of rotavirus diarrhoea in foals by parenteral vaccination of the mares: field trial.

Many countries have reported rotavirus diarrhoea in foals. In Argentina it causes important economic losses to the horse industry. In this work we present the results obtained using an experimental vaccine in a farm with enzootic infection of rotavirus. A hundred mares were vaccinated 60 and 30 days before foaling with inactivated rotavirus SA11 (G3P2), H2 (G3P12), Lincoln (G6P1), with aluminum hydroxide as adjuvant; 65 mares were included in the unvaccinated, control group. To evaluate the vaccine, morbidity, duration of the diarrhoea and rotavirus shedding were recorded. Antibody levels were established in serum, colostrum and milk of the vaccinated mares, and also in serum from the foals. In foals from vaccinated mares the morbidity was 30%, clinical signs were observed during 1.8 days, and rotavirus shedding was not detected. In the control group the morbidity reached 80%, the clinical signs lasted 7.3 days and rotavirus shedding was detected in 80% of the diarrhoeic foals. At foaling the serum antibody levels were 15 times higher with a mean neutralizing titre (NT) of 3.5 logs than before vaccination (2.4 logs), in colostrum 5.00 logs, and in milk at 90 days post partum 1.7 logs. In foals from vaccinated mares the level of neutralizing antibodies was 3.8 logs at 48 days of age, going down to 2.2 logs at 90 days of age. Immunization of the pregnant mare would be a good method for preventing diarrhoea in foals.