Bluetongue in cattle

Diagnosis and virus isolation

Abstract

In certain cattle herds infected with bluetongue virus (BTV) and located in Oklahoma, abortions and developmental anomalies have been observed. Arthrogryposis, scoliosis and kyphosis were present in newborn and fetal calves from several bluetongue-infected cattle. Bluetongue virus was isolated from bone marrow and washed red blood cells from several of these fetuses. Bluetongue serotypes 13 and 17 were identified by serum-virus neutralization from these affected herds. Field isolates of BTV were adapted to cell cultures following isolation in embryonating chicken eggs. Bluetongue virus was highly membrane-associated, which added to the complexity in isolation attempts. However, increased yield of BTV in cell cultures was obtained by continuous gentle rocking during adsorption of virus in cellular monolayers. Serological data obtained from cattle during a 3-year period from July 1, 1978 to June 30, 1981 by complement fixation (CF) and agar-gel immunodiffusion (AGID) tests indicated an infection rate of 68% (1117 of 1629 samples positive) by CF from July 1, 1978 to June 30, 1980 and 49.5% (422 of 852 samples positive) by CF and AGID from July 1, 1980 to June 30, 1981. Recommendations for handling cattle infected by BTV are also presented.