Experimental infection of horses with an attenuated Venezuelan equine encephalomyelitis vaccine (strain TC-83).
Ten horses (Equus caballus) were vaccinated with strain TC-83 Venezuelan equine encephalomyelitis (VEE) virus vaccine. Febrile responses and leukopenia due to a reduction of lymphocytes and neutrophils were observed in all animals. Viremias were demonstrable in eight horses, with a maximum of 10(3.5) median tissue culture infectious dose units per ml of serum in two horses. Clinical illness with depression and anorexia were observed in five horses. Neutralizing (N), hemagglutination-inhibiting, and complement-fixing antibodies to the vaccine virus were demonstrable by 5, 6.5, and 7 days, respectively, after vaccination. Differential titrations of serum to six VEE strains revealed high titers of N antibody to vaccine virus, moderate titers to the epizootic Trinidad donkey no. 1 strain (VEE antigenic subtype I, variant A) from which TC-83 was derived, and low titers to two other epizootic strains (subtype I, variants B and C) in all horses at 1 month after vaccination; some animals responded with low levels of N antibody to the enzootic viruses (subtype I, variants D and E). Fourteen months after vaccination, six animals with detectable N antibody were challenged with MF-8 (subtype I, variant B), an epidemic-epizootic strain isolated in 1969 from a man in Honduras. All horses resisted challenge with the equine pathogenic strain of VEE. Marked increases of N antibody in most horses were demonstrable to some VEE strains when tested 1 month after challenge.
D000818:Animals; D000914:Antibodies, Viral / Q000032:analysis; D001831:Body Temperature; D003168:Complement Fixation Tests; D004666:Encephalitis Virus, Venezuelan Equine / Q000276:immunology*; D004683:Encephalomyelitis, Equine / Q000276:immunology* / Q000517:prevention & control; D006386:Hemagglutination Tests; D006736:Horses; D007109:Immunity; D007970:Leukopenia / Q000209:etiology; D008297:Male; D011507:Proteinuria / Q000209:etiology; D013997:Time Factors; D014611:Vaccination; D014765:Viral Vaccines / Q000009:adverse effects / Q000627:therapeutic use*
D000914:Antibodies, Viral; D014765:Viral Vaccines