Summary (continued)
The EIA virus can be transmitted by horse flies for at least 30 minutes after feeding on a horse with acute signs of EIA, but the probability of a horse fly being interrupted and completing its blood feeding on a second host at a distance of 50 m is very low, and the separation of infected and uninfected equids by 200 m breaks transmission. The statements above assume that human interactions are absent or do not contribute to the risk of virus transmission; however, the risk from human interventions, such as the too-often-used procedure of administering >200 ml of plasma to foals, can easily be more than 107 times greater than the risk posed by a single horse fly. Controlling EIA depends upon the identification of persistently infected equids by serological testing because other methods of identifying infective virus or viral genetic material are less accurate or impractical.