Mechanical transmission of bovine leukemia virus by horse flies (Diptera: Tabanidae).

Bovine leukemia virus was transmitted mechanically to goats and sheep from a cow with persistent lymphocytosis and an infectious titer between 103 and 104 doses/ml by groups of 50 and 100 horse flies, Tabanus fuscicostatus Hine, but not by groups of 25 and 10 flies. A total of 185 flies did not transmit BLV to goats from a cow with a normal lymphocyte count. Transmission trials indicated at least 20% of the 10 nl blood residue on the mouthparts of T. fuscicostatus may be deposited upon a second probe.