Role of horse fly (Tabanus fuscicostatus Hine) and stable fly (Stomoxys calcitrans L.) in transmission of equine infectious anemia to ponies in Louisiana

Studies were carried out in Louisiana on the possible role of Tabanus fuscicostatus Hine and Stomoxys calcitrans (L.) in the mechanical and cyclical transmission of equine infectious anaemia (swamp fever) to Shetland ponies [cf. RAE/B 31, p.102]. In the mechanical transmission experiments with S. calcitrans, the flies were fed individually until partly replete on infected ponies and then immediately after on uninfected ones. Five uninfected ponies each received bites from about 200 adults and one received 10 bites; none became infected. In the cyclical transmission experiments with this fly, 4 uninfected ponies were each bitten by 14-25 flies 3-10 days after a previous feed on an infected one; none became infected. In mechanical transmission experiments with T. fuscicostatus, 6 ponies each receiving 10-200 bites from females that had partly fed on ponies with acute infection, all became infected, but 2 others each receiving bites from 200 females partly fed on ponies with chronic infections failed to become infected. Cyclical transmission attempts with 19 and 25 females fed on 2 ponies were unsuccessful.