Swedish Culex torrentium and Cx. pipiens (Diptera: Culicidae) as experimental vectors of Ockelbo virus.

The ability of the sibling species Culex pipiens (L.) and Culex torrentium (Martini) from central Sweden to transmit Ockelbo (OCK) virus was determined. Both species became infected after ingesting OCK virus from a viremic chicken; they transmitted this virus to chickens after 21-28 d of extrinsic incubation. In Cx. torrentium, infection rates were 90% or higher, and all 10 refeeding mosquitoes transmitted virus after feeding on chickens with a viremia of at least 10(3.0) plaque-forming units (PFU)/ml. In contrast, only 1 of 28 (4%) of the Cx. pipiens that ingested blood containing 10(3.0-3.9) PFU/ml became infected, and none of 16 refeeding mosquitoes transmitted virus. However, 98 of 184 (53%) of the Cx. pipiens that ingested a blood meal containing at least 10(6.0) PFU/ml became infected. Transmission rates in Cx. pipiens increased with increasing virus concentration in the blood meal to a maximum of 37% in mosquitoes that ingested greater than 10(8.0) PFU/ml. Based on these data, both Cx. pipiens and Cx. torrentium are capable of transmitting OCK virus in an enzootic cycle involving birds as hosts. However, Cx. torrentium appears to be physiologically a more efficient vector than Cx. pipiens.