FIELD AND LABORATORY STUDIES OF EQUINE INFLUENZA VIRUS, EQUINE RHINOPNEUMONITIS VIRUS, AND EQUINE ROTAVIRUS

Six outbreaks of equine influenza virus A(,2) (EIVA(,2)) were diagnosed serologically at five different racetracks during 1983-84. EIVA(,2) was isolated from horses at four outbreaks. Only horses which had not been vaccinated within six months became clinically ill. Clinically normal stablemates sampled during these outbreaks showed no serological evidence of subclinical infection. There appeared to be a correlation between hemagglutination inhibition (HAI) titer and susceptibility to disease. Horses vaccinated biweekly appeared to have a statistically significantly higher EIVA(,2) HAI titer than those vaccinated triannually. It was concluded that there had been no significant change in the antigenic components of EIVA(,2).;Twelve pony mares were maintained in isolation units prior to foaling. All foals nursed. At 2 to 12 days of age, 10 foals were inoculated by naso-gastric tube with 10('2.6) to 10('8.6) TCID(,50) of one of two cell (MA104) culture propagated equine rotaviral (ERV) strains. Seven foals exhibited diarrhea and shed ERV for up to 11 days post-inoculation. Two foals, first inoculated at 30 days of age, also exhibited clinical ERV disease. Two foals which remained clinically normal seroconverted to ERV. Eight mares developed increased antibody titers to ERV indicating they had acquired subclinical infections from their foals. All foals were resistant to clinical reinfection with both the homologous and the heterologous ERV strains. It was concluded that: there was no correlation between serum antibody titer and susceptibility to clinical ERV infection; the cross protection between heterologous ERV strains may indicate that only a monovalent ERV vaccine need be developed; asymptomatic infections play a significant role in the epizootiology of ERV disease.;Pre- and post-nursing serum samples were obtained from 50 foals. Bi-weekly serum samples were obtained from 25 foals for eight weeks. Antibody titers to equine influenza viruses A(,1) and A(,2) (EIVA(,1) and EIVA(,2)) and equine herpes virus 1 (EHV(,1)) were measured in serum and colostrum samples. Foal serum antibody and IgG levels were equivalent to those measured in their dam's sera. The half life of maternally-acquired serum antibody in the foals was determined to be: EIVA1 = 28.8 days (26.4 to 31.7 days); EIVA2 = 29.1 days (26.7 to 32.1 days); EHV1 = 31.0 days (28.1 to 34.8 days).