Eradication of bovine brucellosis in the Azores, Portugal-Outcome of a 5-year programme (2002-2007) based on test-and-slaughter and RB51 vaccination.

Bovine brucellosis is an important contagious disease that can cause abortions and infertility in cattle, and can be transmitted to humans. Despite having an eradication programme in place since 1994, in 2000 the situation of bovine brucellosis due to Brucella abortus was not significantly improving in 3 of the 9 islands (Terceira, S. Miguel and S. Jorge) of the archipelago of Azores, an autonomous region of Portugal. Farming on these islands, particularly dairy, is extensive. Therefore, the use of RB51 vaccine, which does not induce antibodies detectable with routine brucellosis diagnostic tests, was implemented. This article reports the results of an eradication programme based on RB51 mass vaccination combined with test-and-slaughter, which was implemented in the Azores during the 2002-2007 period. During the first round of vaccination, both adult cows and heifers were vaccinated. Subsequently, only replacement stock aged 4-12 months, were immunized with RB51.The test-and-slaughter policy based on bulk milk ring test (MRT) and serological surveillance was maintained. During this period, the average brucellosis herd incidence, herd prevalence and individual prevalence decreased 69.26%, 39.26% and 75.41% respectively for the three above-mentioned islands. However, disease reduction approaching eradication was obtained only on the island of Terceira, where a high level of vaccine coverage was rapidly reached and regularly maintained together with strict application of a test-and-slaughter programme. This work shows that the RB51 vaccine could be a useful tool for eradicating bovine brucellosis in well-controlled epidemiological units provided that there is mass vaccine coverage for a sufficiently long period of time and it is combined with an appropriate test-and-slaughter programme.