Bluetongue virus in a Nigerian dairy cattle herd. 1. Serological studies and correlation of virus activity to vector population.

Newborn calves were bled at monthly intervals and examined for serum antibodies to blue tongue virus (BTV). Maternal immunity persisted for 3 months and it was possible to calculate decay rates for virus neutralizing antibody. Calves were subclinically infected with BTV within a few months of becoming susceptible and neutralization tests were used to deduce the serotype responsible. A profile of virus activity was built up over a 12 month period. Frequent light trap catches were used to examine the population dynamics of suspected Culicoides vector species. Two species, imicola and schultzei were present throughout the wet and dry seasons and survival were sufficiently long to account for virus transmission at any time of the year.