Bodies Suggesting Exoerythrocytic Forms of Plasmodium vivax in Tissue Culture.∗

Abstract

The demonstration of exoerythrocytic forms of avian malarial parasites 1 has stimulated a search for similar bodies in mammalian malaria. A few authors have described structures which they believed to be exoerythrocytic forms of human malarial parasites. The subject has been reviewed by Porter and Huff 2 and by Brug. 3 Brug 3 himself presented figures of bodies seen in smears of the lungs of a patient dying in the acute stage of Plasmodium vivax infection which he thought to be exoerythrocytic forms. Recently Raffaele 4 has reiterated the claim that he has seen such forms in all 3 types of human malaria.

To date, demonstration of exoerythrocytic forms has depended largely upon examination of smears and sections of tissues. Recently Hawking 5 , 6 has shown that the exoerythrocytic forms of avian malarial parasites are readily grown in tissue cultures of infected tissues. This has been confirmed P. gallinaceum by Haas, 7 Zuckerman 8 and by the present author. 9 Since methods of tissue culture allow for multiplication of the histotropic forms of the parasites, this technic might prove superior to the use of smears or sections in the search for mammalian exoerythrocytic forms. Accordingly we have made tissue cultures of bone marrow from humans infected with sporozoites of P. vivax or P. falciparum both before and after parasites appeared in the blood.†

As a preliminary measure the technic was tested by cultivating the exoerythrocytic forms of P. gallinaceum from infected chick embryos.‡ These forms grew readily from spleen and liver as well as from brain and lung. 9 Hawking, 5 working with 10-day-old chicks, was unable to grow the parasites from the latter 2 tissues. Our difference in results is probably due to the greater ease with which embryonic tissues are cultivated as well as to the greater number of parasites in the embryonic tissues, as has been shown by Zuckerman. 8

Methods and Materials. Sternal bone marrow punctures were made 4 to 6 days after the initial biting by infected mosquitoes, as well as 7 to 10 days after the development of parasitemia. The specimen was hep-arinized and centrifugalized.