The development and persistence of phanerozoites in experimental infections of Plasmodium sasai

Abstract

Phanerozoites of Plasmodium sasai parasitised virtually all tissues of Takydromus tachydromoides infected by inoculation of blood, and persisted until each lizard died, 2–296 days postinoculation. At 4 days postinoculation, phanerozoites were larger than at 2 and 6 days; many were observed rupturing, suggesting a maturation time of approximately 4 days. The proliferation of phanerozoites decreased after 2 months postinoculation, but small phanerozoites were still present at 296 days. A few encysted phanerozoites (chronozoites) appeared at 2 days postinoculation, but from 75 days comprised over half of parasites present in most tissues. Some differences in mean size and shape were evident among various organs. Phanerozoites occurred in connective tissue and endothelium in all organs, but were most plentiful in the heart in every infection, often occurring in clusters of >30 schizonts, with up to 105 found in single sections at 4 days. Phanerozoites did not parasitise reticular cells of the spleen and bone marrow, in contrast to Plasmodium mexicanum as described in unnatural host species. Little difference was seen between two strains of P. sasai in its natural host T. tachydromoides and a strain isolated from Takydromus smaragdinus.