Tabanid (Diptera) populations associated with an equine infectious anemia outbreak in an inapparently infected herd of horses.

Seven horses positive for antibodies to equine infectious anemia virus in the agar gel immunodiffusion test were maintained together with 8 test-negative horses in an isolated pasture in south Louisiana for 1 year. Although the test-positive horses were inapparently infected (exhibiting no clinical signs of equine infectious anemia), 6 of the 8 test-negative horses became test-positive during 1 vector season. Canopy trap surveillance revealed Hybomitra lasiophthalma as the only tabanid species present during 2 equine infectious anemia virus transmissions in March. A high population of Tabanus lineola was present during the remaining 4 virus transmissions in July, September, and October.