CALIFORNIA ENCEPHALITIS GROUP VIRUSES ISOLATED FROM MOSQUITOES COLLECTED IN SOUTHERN AND ARCTIC NORWAY

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Abstract
Three virus strains serologically related to the California encephalitis group (Bunyaviridae) of arboviruses were isolated from 7331 mosquitoes collected in Norway in June‐August 1975. Two of the isolates (S 548 and S 618) seemed to be closely related and the third. S 568. more distantly related by serological techniques to Tahyna virus. Viruses were found in the mosquito species Aedes sticticus, A. diantaeus and A. hexodontus collected (in order) from Øyern (59° 50′ N, 11° 12′ E), Trandum (60° 08′ N, 11° 10′ E) and Masi (69° 26′ N, 23° 39′ E). The Masi isolate seems to be the northernmost arbovirus isolate in the world so far. Strain S 568 was from 16 ♂♀A. diantaeus, indicating transovarial transmission of the virus. An accidental infection demonstrated the potential human pathogenicity of one of the newly‐isolated strains (S 568), and the ability of CE viruses to persistently infect suckling mouse brains was indicated by in vivo findings. The biological characteristics of the new strains so far investigated are consistent with those of the California encephalitis group. During this work the Aerosil absorption method for production of haemagglutinating antigens proved useful for Tahyna virus and the newly‐isolated strains. Trypsinization of erythrocytes improved the haemagglutinating capacities of these viruses.