Prevalence of Bluetongue virus serotype 4 in cattle in the State of Sao Paulo, Brazil.

Bluetongue (BT) is considered endemic in several regions of Brazil. The State of Sao Paulo was divided into 7 cattle production regions (circuits) according the different systems of breeding, operational and logistical capacity of the state veterinary service. At least 1 animal from each property (a total of 1,716 farms) was tested by competitive ELISA for the presence of antibodies against BTV. Sero‑positive sera were subsequently also tested by virus neutralization tests (VNT) using serial dilutions from 1:10 (cutoff) up to 1:640 (in MEM). BTV‑4 neutralizing antibodies were detected in 86% (1,483/1,716) of the animals tested. These results show that BTV‑4 is endemic and widespread in the State of San Paulo and indirectly confirm that in the State there are favourable conditions for the multiplication of competent vectors. However, as no clinical signs have ever been reported in cattle in the region, BTV‑4 infection is likely to occur silently in the State of Sao Paulo.