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

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... 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.