a1 National Institute for Medical Research, Mill Hill, London, N.W.7 and the Infestation Control Division, Ministry of Agriculture, Fisheries and Food, Tolworth, Surrey
Anopheles labranchiae atroparvus which have gorged on myxoma-infected rabbits may retain their infectivity for as long as 220 days in a period covering the winter months. Virus titres in infected mosquitoes may also remain stable for several weeks at summer temperatures; virus has been recovered after 36 days in summer.
Virus in these Anopheles is, in most instances, to be found only in the head and mouthparts. Survival on mouthparts of killed mosquitoes, on the other hand, has been only for a few days.
One strain of virus (Newhaven strain) isolated from wild A. atroparvus produces flat erythematous lesions on intradermal inoculation into rabbits, and deaths occur later than with typical strains.
The possible role of over-wintering atroparvus as a reservoir of infection of myxomatosis is discussed.
The possibility is considered that transmission of infection by Anopheles is not purely mechanical, but that limited multiplication occurs in the insects.
c1 In receipt of an expenses grant from the Agricultural Research Council.