Plasmodia were found by electron microscopy within platelets of two men with naturally acquired, acute malarial infections (Plasmodium vivax). A parasitized platelet was also discovered in one of these patients after he was clinically cured. In addition, parasites have been demonstrated within platelets of more than 50% of mice infected with P berghei. The plasmodia probably penetrate after the platelets have detached from megakaryocytes, because the latter have normal ultrastructure, even in heavily parasitized hosts. The mechanism of penetration is not clear, but the morphologic data suggest that merozoites may actively invade the platelets. Parasitization of the platelets may be a cause of malarial thrombocytopenia.
(JAMA 229:1205-1207, 1974)