Bunyavirus isolations from mosquitoes in the western Canadian Arctic

Strains of California encephalitis virus (snowshoe hare subtype) were isolated from 8 of 475 pools comprising 23 747 unengorged female mosquitoes of five species collected at three of six locations throughout the Mackenzie Valley of the Northwest Territories, Canada, from latitudes 60 to 69 degrees N between 10 and 24 July 1976. Minimum field infection rates included 1:2734 for Aedes communis, 1:256 to 1:3662 for A. hexodontus and 1:911 to 1:1611 for A. punctor. Northway virus was also isolated from 1 of 3662 A. hexodontus mosquitoes collected at Inuvik (69 degrees N, 135 degrees W). Transmission of CE virus by A. communis infected by feeding on virus in defibrinated blood and incubation at 0, 13 and 23 degrees C for 13-20 days clearly demonstrates the importance of this species as a natural vector, and transmission of CE virus by Culiseta inornata after incubation at 0 and 13 degrees C following intrathoracic injection strengthens evidence of its role as a natural vector. Immunofluorescence was less reliable than imunoperoxidase for detection of CE viral antigen in mosquito salivary glands.