Transmission of equine infectious anemia virus by Tabanus fuscicostatus

In studies in Louisiana, adults of Tabanus fuscicostatus Hine were fed on Shetland ponies that had been infected with equine infectious anaemia when these had a rectal temperature of above 39.5 deg C. After a partial feed, the flies were transferred to susceptible Shetland ponies immediately after feeding or after an interval of 3, 10 or 30 min or 4 or 24 h. In 1 of 7 tests with single flies re-feeding immediately after the initial feed, transmission of the virus occurred. Groups of about 25 flies re-feeding after intervals of 3, 10 or 30 min transmitted the virus in each of 2 tests at each interval, but no transmission occurred in 2 tests each with re-feeding after intervals of 4 or 24 h. As tabanids are known to have flight distances or home ranges that may exceed 4 miles, the present practice of segregation of infected horses at least 200 yeards from susceptible ones as a control measure may be inadequate. Mechanical transmission by biting flies is considered to be a major natural method of transmission of equine infectious anaemia virus.