Active circulation of bluetongue vaccine virus serotype-2 among unvaccinated cattle in central Italy.

Several seroconversions occurring in 2002 among sentinel cattle during the bluetongue-vaccination campaign in Lazio and Tuscany (central Italy) led to the suspicion of vaccine-virus circulation. Therefore in 2003, 17 seroconverting sentinel herds were investigated for the characteristics of the virus involved. From these farms, 91 unvaccinated animals and 57 Culicoides pools were tested for the presence of the bluetongue vaccine virus (serotype-2) or other strains. The presence of vaccine virus serotype-2 was confirmed by PCR followed by restriction analysis in the whole blood of 17 unvaccinated sentinel cattle and 12 pools of Culicoides imicola or C. obsoletus. Of the 17 herds, five were positive only for vaccine virus serotype-2, four were positive for other strains and two for both the vaccine and other strains; the remaining premises were virologicaly negative. The vaccine virus serotype-2 also was detected in areas not included in the vaccination campaign.