A curious aspect of the evolution of the hypnozoite theory of malarial relapse is its transmogrification from theory into ‘fact’, this being of historical, linguistic, scientific and sociological interest. As far as it goes, the hypnozoite explanation for relapse is almost certainly correct. I contend, however, that many of the genotypically homologous, non-reinfection, relapse-like Plasmodium vivax recurrences that researchers ascribe to hypnozoite activation are probably hypnozoite-independent. Indeed, some malariologists are starting to recognize that homologous P. vivax recurrences have most likely been overattributed to activation of hypnozoites. Hitherto identified, non-hypnozoite, possible plasmodial sources of recurrence that must be considered, besides circulating erythrocytic stages, include parasites in splenic dendritic cells, other cells in the spleen (in addition to infected erythrocytes there), bone marrow (importantly) and the skin. I argue that we need to take into account the possibility of a dual or multiple extra-vascular origin of P. vivax non-reinfection recurrences, not arbitrarily discount it. The existence of a P. vivax reservoir(s) is a topical subject and one of practical importance for malaria eradication. Pertinent drug-associated matters are also discussed, as is the dormancy-related significance of clues provided by blood-stage-induced malarial infection.

The study of malaria in the laboratory relies on either the in vitro culture of human parasites, or the use of non-human malaria parasites in laboratory animals. In this review, we address the use of non-human primate malaria parasite species (NHPMPs) in laboratory research. We describe the features of the most commonly used NHPMPs, review their contribution to our understanding of malaria to date, and discuss their potential contribution to future studies.