The Behavior of the Avian Malarias in the Common Fowl, and Abnormal Host

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Abstract
Summary and Conclusions It has been shown from the study of thirty-five chickens which have been inoculated with malarial parasites belonging to the species praecox, circumflexum, cathemerium, rouxi and elongatum that genuine infections can be produced with the first three of these five species, but that the parasite-level in these infections is usually too low for microscopic demonstration, so that detection is only possible by inoculation of massive doses of chicken blood into fresh canaries. Canary subinoculation was not tried on intramuscularly inoculated chicks but microscopic study of blood films from such chicks never revealed parasites. Infections lasting from three to ten days were uniformly produced by intravenous inoculation, in the case of Plasmodium praecox, circumflexum and cathemerium. In several cases there were enough parasites in the blood of such birds to demonstrate easily in stained films. The following conclusions therefore seem warranted: 1. The common chicken (Gallus gallus) is susceptible to infection with Plasmodium circumflexum, praecox and cathemerium, but not with rouxi and elongaturn, although plasmodia of the last two species may remain viable in the blood for some hours. 2. Malarial infection with the three species named above is a much different matter in the chick than in the canary, and the parasite-level is generally so low that the presence of an infection can be demonstrated only by subinoculation of chicken blood into clean canaries. Since the length of the incubation period in such canaries is usually greater than that in birds inoculated with comparable quantities of blood from canaries carrying chronic infections, it is reasonably certain that the parasite-level in chickens is usually lower than that in such chronic cases. Gametocytes have been observed in blood films from malaria-inoculated chickens in certain cases, and this fact makes it virtually sure that mosquitoes could be infected from these cases at least. Although it is a sufficiently well-known fact that a given parasite may produce an infection of a much different type in a host which is not its normal one (as is the case of Trypanosoma equiperdum, which is one thing in the horse, another in the rat and still another in the guinea-pig) the production of a latent infection such as that here demonstrated in the chick suggests that unrecognized hosts of certain parasites—and conceivably of human malaria—may perhaps exist in nature. 3. Although chickens are susceptible to malarial infection with the species of plasmodia named above, they are much more resistant than birds such as the canary, and the parasites seem able to maintain themselves for only a few days. In no case was an infection proved to last more than ten days. 4. If malaria parasites have ever been observed in the blood of the domestic fowl it is virtually certain that they did not belong to any one of the five species used in the present study, and hence would constitute a new species.

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