Bluetongue virus in pregnant elk and their calves.
Two pregnant North American elk (Cervus canadensis), in the 3rd and 4th months of gestation, were inoculated with bluetongue (BT) virus (BTV) serotype 11. The virus was not isolated from the blood of the cows beyond postinoculation day (PID) 8, but was isolated from bone marrow and spleen samples obtained at necropsy on PID 190. Although neither cow had overt clinical signs of BT infection, fluctuations in specific neutralizing BTV antibody titers indicated viral replication. However, in 2 attempts, BTV was not recovered biologically via bites of colonized Culicoides variipennis (biting gnats) with subsequent transmission of the BTV to sheep. Bluetongue virus was isolated from the elk calves at birth and before they nursed. These calves remained latently infected, and BTV was transmitted from each calf to sheep by bites of the biting gnats. Most of the BTV biological recovery attempts resulted in suspicious BT clinical responses in sheep, but without viral isolation. However, after challenge exposure with the homologous virus, 5 of 7 recipient sheep bitten by the gnats reacted with an intensified BT clinical response that indicated viral sensitization. One calf was born weak, never attained a healthy appearance, was latently infected with BTV, and had fluctuating BTV neutralizing antibody titers. The other calf was in apparently good health, was latently infected with BTV, and was immunologically tolerant to BTV.