Brucella abortus biovar 3 is implicated in an outbreak of abortion in a dairy cattle farm immunized with Brucella abortus Iriba vaccine
Bovine brucellosis is a widespread zoonosis caused by Brucella abortus. The disease is prevalent nationwide in Iran and the rate of infection is dramatically increasing between human and livestock. Eradication of brucellosis is challenging and requires control policies at both national and regional levels. The aim of the current study was to evaluate if Brucella is implicated in an outbreak of abortion occurred in dairy cattle herd after vaccination with B. abortus Iriba vaccine. Our study was done following an outbreak of abortion in a dairy cattle farm with 2000 animals located in the Shahre Rey of the Tehran province, Iran. This farm was described as Brucella free after two seronegative results one month before vaccination. After appearance of first case of abortion, serodiagnosis revealed seropositive reaction in 30 non-pregnant cows and in 19 pregnant cows that have been aborted later. Bacteriology and molecular typing succeeded to identify 16 isolates of B. abortus biovar 3 from aborted animals. None of isolates was confirmed as B. abortus Iriba vaccine strain. Results confirmed that B. abortus biovar 3 remain the most prevalent biovars in cattle of Iran. Source and time of infection in the current study is not determined and most likely is due to low biosecurity level in the farm e.g. uncontrolled introduction of the agents via persons, infected animals, semen and vectors. In endemic countries, serodiagnosis of brucellosis alone is not sufficient and has to be accompanied with isolation and molecular diagnosis. Also, it is important to evaluate the presence of B. abortus in bovine semen and vectors.