Bluetongue virus infection in sheep: haematological changes and detection by polymerase chain reaction

Eight sheep vaccinated with 10(6) pfu of attenuated Australian bluetongue virus serotype 23 (BTV 23A) and eight BTV-free sheep were challenged with virulent BTV 23. There was little subsequent variation in the mean clinical score, or in the mean lymphocyte and platelet concentrations in the peripheral blood of the eight vaccinated sheep. There was a marked thrombocytopenia and lymphopenia in the naive sheep as the mean lymphocyte and platelet concentrations fell to a minimum at days 8 and 11 after inoculation, respectively. Similar changes were observed in three other naive sheep inoculated with field isolates of BTV 1,9 or 23. BTV was detected by nested polymerase chain reaction in whole blood of these sheep between days 6 and 28, in mononuclear leukocytes between days 3 and 14, and in platelets between days 6 and 21.