Sections of paraffin-embedded rhesus liver containing numerous nearly mature exoerythrocytic schizonts of the non-relapsing malaria parasite, Plasmodium knowlesi, were examined for the presence of hypnozoites by indirect immunofluorescence, employing both homologous and strongly cross-reacting heterologous sera. No hypnozoites or evident hypnozoite equivalents were detected in tissue which, by analogy with results obtained for the relapsing species, P. cynomolgi bastianellii, should have contained 35–50 of the uninucleate forms. These observations are presented as additional evidence in favor of the hypnozoite theory of malarial relapse.
Formerly Chief, Tropical Infectious Disease Research Program, U.S. Public Health Service Hospital, New Orleans, Louisiana 70118.
Deputy Chief, Malaria Branch, Parasitology Division, Center for Infectious Diseases, Centers for Disease Control, Atlanta, Georgia 30333.