Experimental Studies of Concurrent Infection of Canaries and of the Mosquito Culex Tarsalis with Plasmodium Relictum and Western Equine Encephalitis Virus

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Abstract
Summary A report is presented of the results obtained in a study designed to test the hypothesis that avian malaria plasmodia acquire and retain, for considerable lengths of time, the virus of Western equine encephalitis in infected birds. Experiments were performed to determine the virus concentration of plasmodia-infected blood cells from canaries concurrently infected with both agents and in blood cells from canaries infected with the virus only. The duration of viremia in birds suffering concurrent infection with both agents and in canaries infected with virus only was also determined. These and other studies failed to support the stated hypothesis. Quite the contrary, it was found that concurrent infection of canaries with avain malaria and with encephalitis virus resulted in a significant suppression of virus titer in such birds. This virus titer suppression could not be correlated with the degree of parasitemia, and did not occur in birds in the latent stage of malaria infection. Concurrent infection of the mosquito Culex tarsalis with the avian malaria parasite Plasmodium relictum and Western equine encephalitis virus did not detectably alter the ability of this mosquito to transmit virus. Mosquitoes with such concurrent infections transmitted virus in 42 per cent of all attempts, whereas mosquitoes infected solely with virus transmitted in 45 per cent of all attempts. It was pointed out, however, that results of viremia studies on canaries, indicate that concurrent infection of such birds with the two agents suppresses the level of viremia, and that some birds develop virus titers too low to render mosquitoes infective. The possible importance of this phenomenon in the epidemiology and epizootiology of Western equine encephalitis is discussed.