Serological evidence of bluetongue and a preliminary entomological study in southern Croatia.

In December 2001, bluetongue (BT) was confirmed serologically by the Croatian Veterinary Institute using the competitive enzyme-linked immunosorbent assay (c-ELISA). Results of the serological testing of blood samples from ruminants in the Dubrovacko-Neretvanska County are presented (3,318 sera of ruminants from 53 herds were examined). In total, 357 bovine sera (178 or 49.9% positive), 1,268 ovine sera (174 or 13.7% positive) and 1,693 caprine sera (270 or 15.9% positive) were tested. Antibodies to BT virus serotype 9 were detected in 212 of the positive sera by serum neutralisation. A preliminary light-trap survey for midges of the Culicoides genus was also performed in the Dubrovacko-Neretvanska County. Fourteen light-trap collections from seven locations were examined and yielded a total of 4,872 Culicoides of which 4,492 (92%) belonged to the Obsoletus Complex (including C. obsoletus and C. scoticus).

Spatial distribution of bluetongue in cattle in southern Croatia in the last quarter of 2002.

The domestic ruminant population of southern Croatia was affected by bluetongue (BT) in late 2001. A sentinel cattle scheme was developed to detect the presence of bluetongue virus (BTV) activity in the domestic cattle population in the protection zone (based on the distribution of BT in 2001: Dubrovacko-Neretvanska County and the southern area of the Splitsko-Dalmatinska County) as well as in the surveillance zone (the northern area of the Splitsko-Dalmatinska County). Twenty-five villages were selected to serve as sentinel locations during the observation period which lasted from 15 September to 15 December 2002. Seroconversion was not detected in cattle in sentinel locations in the surveillance zone. However, in the protection zone, serum antibodies to BTV serotype 9 were detected in eight cattle in five of the ten sentinel locations. Although no clinical case of BT disease was detected in sheep on mainland Croatia in late 2002, BTV activity was present in sentinel cattle in the protection zone. When compared with 2001, spatial distribution of the locations in which cattle seroconverted to BTV-9 in the last quarter of the 2002 suggests a northward trend to the spread of BTV in the cattle of southern Croatia.