Adverse response of non-indigenous cattle of European breeds to live attenuated Smithburn Rift Valley fever vaccine.

ABSTRACT

Three hundred eighteen European cows and 115 buffaloes were vaccinated with locally prepared Smithburn vaccine, of which, 100 cows and 20 buffaloes were pregnant. Twenty-eight cows aborted within 72 days post-vaccination, buffaloes did not abort. Blood samples collected 77 days post-vaccination from aborted cows, 17 pregnant cows, 5 pregnant buffaloes, and 32 non-pregnant cows. Sera were tested by ELISA for anti-RVF IgM and IgG. All aborted cows were strongly positive for IgG. Five of 17 cows and two of five buffaloes that did not abort were IgG positive. The percentage of IgM positives in aborted cows was 25% and 0% in non-aborted cows. The percentage of IgG positives in pregnant non-aborted cows was lower than in non-pregnant cows. The percentage of IgG positives of non-pregnant cows was lower than pregnant aborted cows. Virus was isolated from one aborted fetus. The nucleotide sequence of fetus virus was compared to Smithburn of Onderstepoort, local Smithburn and virus isolates from 1993 to 1994 and 1977 RVF outbreaks. The nucleotide sequences of Onderstepoort and Egyptian Smithburn vaccines were almost identical. The sequences of 1993-1994 isolates were identical to 1977 outbreak virus. Virus from the fetus had two mutations; it is apparently a variant that is genetically distant from local Smithburn and Onderstepoort vaccines. Fetus virus was genetically distant from virus of 1993/1994 and 1977 outbreaks. In conclusion, antibody response to vaccination with local Smithburn had occurred in some, but not all the cows and buffaloes. Virus isolation from the fetus suggests in utero transmission of used vaccine virus, which resulted in high abortions in European cows.