Quinine and Plasmochin Therapy in Plasmodium Rouxi Infections, with Further Notes on the Effects of These Drugs on the Other Avian Malarias

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Abstract
Summary and Conclusions The work herein described has had for its object the solution of the problem as to whether the two species of avian plasmodia most refractory to treatment could be more successfully treated with a combination of plasmochin and quinine, than with either drug used separately, and further investigation of the effect of plasmochin upon Plasmodium elongatum, shown in previous work to be very highly susceptible to plasmochin. Plasmodium rouxi, an Algerian species, has also been studied with reference to its chemotherapy and the results compared with those obtained by the same methods on the other three species. The question of the reliability of splenomegaly as an indication of malarial infection has also been investigated. A total of 120 cases have been treated, 44 have been used as controls, and 101 others have been used in testing for sterilization and in other ways. Allowing for duplications, 223 birds have been used. The following conclusions seem justified: 1. Infections with Plasmodium praecox and Plasmodium cathemerium can not be more successfully treated with a combination of plasmochin than with either drug separately, or at least such an advantage, if it exists, is slight. The results obtained in these researches gave no suggestion that such a superiority obtains. 2. Wide differences have been shown to exist in the susceptibility of different birds to treatment, when infected with Plasmodium elongatum, and these are interpreted as meaning that the effect of the drug used—plasmochin—is exerted indirectly, through a stimulation of some sort to the natural defensive powers of the host, as well as directly upon the parasite. In general, about four days of treatment appear to be necessary to prevent the development of the infection when started immediately after inoculation, and about twelve days appear to be required for sterilization when administration is deferred until parasites are evident in the blood. 3. Plasmochin exerts a direct plasmodicidal action, when parasites belonging to the species elongatum are exposed to the drug in vitro, but the action is slow and apparent only after a number of hours. Morphological changes are produced more quickly in the parasite than are changes in infectivity. 4. Plasmodium elongatum infections are less easily treated with plasmochin after they become chronic, but it is certain that the parasite level is forced down to a very low level—so low that the blood is no longer infective to clean birds—and that the level remains at this low point in most cases for at least two weeks, even though it is not fully demonstrated that sterilization occurred. 5. Infections with Plasmodium rouxi are as suceptible to plasmochin as are those of elongatum, and more susceptible to quinine than any of the other three species. Sterilized cases are as readily reinfected as when infected the first time. 6. The parasite-level establishes itself at a much higher point with chronic cases of Plasmodium rouxi than in chronic cases of any of the other three species studied. 7. Splenomegaly is not a trustworthy means of diagnosis in avian malaria, particularly chronic cases, since it may be absent, even when parasites are easily demonstrable in the blood, and is often present in birds dying from other causes and known to be, and to have always been, free from malaria. Even the color of the spleen is not a reliable indication, unless it is very dark.

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