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 anaemia virus in the agar gel immunodiffusion test were kept with 8 test-negative horses in an isolated pasture in south Louisiana for a year. Although the positive horses exhibited no clinical signs of equine infectious anaemia, 6 of the 8 negative horses became positive during one vector season. Canopy trap surveillance revealed Hybomitra lasiophthalma as the only tabanid species present during 2 equine infectious anaemia virus transmissions in March. A high population of Tabanus lineola was present during the remaining 4 virus transmissions in July, September, and October.