Subclinical bluetongue virus infection in domestic ruminants in Taiwan

Bluetongue is an arthropod-borne viral disease affecting domestic and wild ruminants. Taiwan, with the Tropic of Cancer crossing through it, was considered free of bluetongue virus (BTV) before 2001. The goals of this study are to identify the serotype and phylogeny of Taiwan BTV isolates and to understand the serological status and chronology of BTV infection. Analysis of the S10 gene segment revealed that Taiwan BTV isolates are closely related to Chinese strains. Seropositive results were found in 32.7% of the cattle and 8.2% of the goats by head, and 90.7% of the cattle herds and 28.9% of the goat flocks. Anti-BTV antibodies have existed in goat sera since 1989 and in bovine sera since 1993, and over the years, the seropositive rates in rapidly urbanized districts have decreased, most likely due to the loss of vector habitats. Seropositive rates for sheep were variable, due to a small sample size and a small sheep population. Thus far, all natural BTV infections have been subclinical, consistent with experimental sheep inoculation, revealing that the Taiwan isolate is of low virulence.