An electron microscopic study of blood cells from calves experimentally infected with bluetongue virus.

Cellular elements from blood samples of calves experimentally inoculated with a quadrivalent mixture of bluetongue virus (BTV) types 10, 11, 13 and 17 were examined by transmission electron microscopy (TEM). Virus-like particles were observed within cytoplasmic vacuoles of infected agranular leukocytes from inoculated calves on postinoculation day (PID) 14. No virus-like particles were seen associated with other cellular blood elements nor were they observed in blood samples obtained prior to virus inoculation. The intravacuolar viral particles were 60nm in diameter, had a cockleburr appearance and lacked the outer polypeptide coats of mature virions. Increased cytoplasmic vacuolation was the most noticeable change in the infected cells. BTV infection was confirmed by viral isolation and serological testing. Pyrexia was the only consistent clinical sign seen in the viremic calves.