Other Haemosporidia which are very important in diseases of domesticated animals, but not for man, are those of the piroplasm type.
These parasites of the red cells do not produce pigment and do not “exflagellate.” It is to parasites of this type that some authorities have ascribed the cause of blackwater fever, a condition undoubtedly connected with malaria.
It has been thought proper by some to consider the malarial parasites as belonging to two genera, the genus Plasmodium, characterized by round sexual forms and including P. vivax and P. malariae and the genus Laverania, characterized by crescent-shaped sexual forms and including but one species L. malariae, that of aestivo-autumnal malaria.
Craig recognizes a quotidian form and a tertian form for the aestivo-autumnal parasite. Manson formerly held the view that three different species of crescent-bearing parasites were concerned in malignant infections; one, of tertian periodicity, Laverania malariae, and two, of quotidian periodicity, L. praecox, a pigmented form, and L. immaculata, a form in which pigment is only observed in the crescent formation and does not exist in the ring form schizonts. He has abandoned this view. Stephens has noted a parasite which has more nuclear material than P. falciparum (P. tenue).
Malaria of Animals.—Other Haemosporidia of the haemamoeba type are found in birds, monkeys, bats, squirrels and possibly in reptiles (the parasites of reptiles, while intracorpuscular and pigment producing, do not exflagellate). Of particular interest is the so-called bird malaria or Proteosoma, a parasite very similar to the human malarial ones.
The life cycle of this parasite was demonstrated before that of the malarial parasites of man.
Although Koch in his work showed that these malaria-like parasites of other animals were not infectious for man, Fermi has recently carried out well-controlled experiments, by feeding laboratory bred anophelines on the blood of various animals showing such infections, and subsequently on men, with invariably negative results.
Accumulated experience shows that man is not susceptible to any of the animal malarias and that the three human species can only exist in man as an intermediate host and in certain species of anopheline mosquitoes as definitive hosts. Culicine mosquitoes never transmit malaria.
Malaria-Transmitting Mosquitoes.—In the United States, Cellia albimana, C. argyrotarsis, Anopheles crucians, A. quadrimaculatus and A. pseudopunctipennis are efficient transmitters of malaria. Rather remarkable is the experience of Beyer in New Orleans that A. crucians will only transmit P. falciparum while A. quadrimaculatus will transmit P. vivax and P. malariae, but not P. falciparum. Further experiments have shown that A. crucians will transmit P. vivax as well as P. falciparum.
As showing the uncertainty attaching to the question of a certain anopheline species being efficient hosts for malaria may be cited the case of A. punctipennis. This species has been frequently reported as incapable of transmitting malaria and quite recently Mitzmain reported experiments on 219 females of the species which had fed on crescent containing blood and which were dissected from three to thirty-eight days after such feedings with negative findings in stomach and salivary glands. Furthermore, these mosquitoes failed to transmit malaria to healthy persons. Control experiments with A. quadrimaculatus and A. crucians were successful. In June, 1916, Dr. King reported 33% of positive findings after dissection of A. punctipennis which had fed on malignant tertian cases and 85% of success where the man bitten had benign tertian malaria. These results showed as high a degree of success as that obtained with the control A. crucians and A. quadrimaculatus.