The late primary exo-erythrocytic stages of Plasmodium malariae

A chimpanzee was inoculated intravenously with sporozoites of the VS strain of P. malariae. The animal had previously been inoculated with the blood stages of the same strain, and was in a state of premunition. Biopsies of the liver revealed plentiful exo-erythrocytic schizonts on the 12th, 13th, 14th and 15th days after inoculation of sporozoites. No secondary forms were seen in a biopsy taken on the 87th day. One mature schizont was found on the 14th day, but the main rupture took place on the 15th day. Characteristic features of the schizonts include: enlargement of the nucleus of the host cell; numerous peripheral and internal vacuoles, containing orange-staining globules; absence of cytomeres, but presence of large clefts; red staining strands and plaques in the 15th-day schizont; the mature schizont measures about 56 μ and contains approximately 15,000 merozoites. Premunition had no effect on the exo-erythrocytic stages of the parasite.