From January, 1956, through April, 1960, 171,210 culicine mosquitoes from Ndumu, Natal, Union of South Africa, were inoculated into mice in 2,325 lots for attempted virus isolation. Fifty-nine recoveries of viruses were effected.
The viral isolates, including nine identified viral types, were recovered from nine species of mosquito, but among these the only ones principally concerned were Aedes (Neomelaniconion) circumluteolus (Theobald), Culex (Culex) univittatus Theobald, Mansonia (Mansonioides) africana (Theobald) and Mansonia (Mansonioides) uniformis (Theobald), in the order named.
The incidence of viral isolates in time and space at Ndumu indicates the possibility of the following assumptions having some basis in fact: (a) host specificity of most of the viruses concerned is not strict among genera of the tribe Culicini; (b) the virus types occurring in the Ndumu region may have undetected local cryptic cycles, their episodic reappearances being accounted for less by foreign reintroduction than by the occasional conjunction of ecological conditions that permits them to enter mosquito cycles detectable by current methods of investigation.
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