Immunity to Cross-Infection in Avian Malaria Due to Plasmodium Vaughani

Abstract

For many years it was believed that infection with one species of avian malaria conferred protection against subsequent infection with that species only, and one of the tests by which a given species could be differentiated from another was to inoculate a subpatent or chronic infection of the former with the suspected new species. Recently it has been shown by Gingrich and others that this is not always the case, but this method is still an important test of specificity. The species used in the present work was originally described by Novy and MacNeal from the common robin in 1904, and the strain employed was isolated from a catbird caught in Syracuse in April, 1934. The other species with which P. vaughani was crossed were secured from sources previously mentioned by the author., Female canaries were used throughout. Before inoculating a bird with a latent infection the continued presence of an infection was checked either by microscopic examination or (since this is usually negative) by subinoculation into fresh birds. Inoculations were generally intravenous, and large doses of parasites were usually used. Ten series of 3 birds each (in addition to one or more controls in each series) were used, 5 being chronic cases of P. vaughani and the others consisting of one series each of P. cathemerium, praecox (relictum), circumflexum, elongatum, and rouxi. Each series of chronic vaughani infections was inoculated with one of the other species named, and the experiment was then reversed, using chronic infections of the latter. The results show that a subpatent (chronic) infection with P. vaughani confers little if any protection against subsequent infection with the 5 other species named, and the reverse of this relationship appears to hold true also, except that there is some indication that a pre-existing infection with P. praecox (relictum) gives a partial immunity to subsequent infection with P. vaughani.