Role of horse flies in transmission of equine infectious anemia from carrier ponies

Equine infectious anaemia virus was transmitted from an acutely ill and an inapparently infected pony to uninfected ponies by the interrupted feeding of wild-caught adults of Hybomitra lasiophthalma (Macq.), Tabanus quinquevittatus Wied. and T. sulcifrons Macq. Transmission from acutely ill ponies was not accomplished following the interrupted feeding of a single tabanid, bites of tabanids that had fed on an acutely affected pony 24 h earlier, bites of tabanids that had oviposited after feeding on an acutely affected pony, or the inoculation of larval material derived from tabanids that had fed to repletion. It was concluded that tabanid transmission of equine infectious anaemia virus is mechanical only and that infected horses that are free of clinical signs can be a source of virus for insect transmission.