Contagious bovine pfeuropneumonsa (CBPP) vaccine strains 11 44 and T1 SR: a dose effect trial

摘要

When CBPP was reintroduced in Botswana in 1995 after more than 50 years of absence (Amanfu, 1998), a logical strategy was put in place to contain the spread of the disease by forbidding cattle movement from the infected zone towards free areas and toperform a massive vaccination campaign ahead of the disease front. The vaccine used was the T1 SR strain and it was administered to thousands of cattle in an emergency vaccination campaign. However logical the strategy and correct the implementation plans were, they failed to contain the disease. CBPP soon spread to regions where the vaccination had been performed. Subsequently, an ultimate massive slaughter strategy was put in place and all the cattle population in the infected zone were destroyed. This enabled Botswana to regain its CBPP-free status by the most rapid way although at a high initial cost. One of the tentative first explanations for the failure of the vaccine strategy was to advocate an error that could have been made when handling theseed strain of vaccine, a less potent strain might have replaced the original one. This proved not to be the case, as a subsequent polymerase chain reaction (PCR) technique (Lorenzon, 2002) clearly identified the vaccine used in Botswana as T1. The quality of the vaccine itself was not considered as a possible cause for the failure, given that it had passed ail the internal controls by the producer and also from an independent laboratory (PANVAC) in Ethiopia.