As ''Culicoides'' midges are biological vectors of BTV, the virus replicates in insect tissue after feeding on an infected host. thus the virus replicates within the tissues of each insect after infection from feeding on the blood of a BTV-infected ruminant [22]. Vector insects can only transmit BTV to another susceptible ruminant after an extrinsic incubation period of some 10 - 14 days, during which time the virus is disseminated from the insect's gut to its salivary glands. The external incubation period is shorter when insects are held at high ambient temperatures. Vertical transmission with transovarial transfer of BTV has not been demonstrated in Culicoides insects, however, infection of adult insects is lifelong. Furthermore, individual insects can survive for relatively long periods of time, particularly in cooler ambient temperatures [23]. | As ''Culicoides'' midges are biological vectors of BTV, the virus replicates in insect tissue after feeding on an infected host. thus the virus replicates within the tissues of each insect after infection from feeding on the blood of a BTV-infected ruminant [22]. Vector insects can only transmit BTV to another susceptible ruminant after an extrinsic incubation period of some 10 - 14 days, during which time the virus is disseminated from the insect's gut to its salivary glands. The external incubation period is shorter when insects are held at high ambient temperatures. Vertical transmission with transovarial transfer of BTV has not been demonstrated in Culicoides insects, however, infection of adult insects is lifelong. Furthermore, individual insects can survive for relatively long periods of time, particularly in cooler ambient temperatures [23]. |