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Can P. vivax sporozoites having the same genotype be both tachysporozoites and bradysporozoites?

December 2, 2021 - 01:13 -- Miles Markus

Lysenko et al.’s hypothetical P. vivax tachysporozoites [1] multiply in the liver soon after inoculation into the host, whereas their hypothetical bradysporozoites form hypnozoites [1], which are the origin of relapses. This "tachy" and "brady" terminology is an extension of usage unrelated to malaria [2].

For a homologous P. vivax malarial recurrence to be a relapse means that firstly, a tachysporozoite(s) will have had to initiate what became a patent infection. But it also means that a sister sporozoite(s) with basically the same genotype must have been, simultaneously, a bradysporozoite(s). This is how hypnozoite-derived recurrent parasites in the bloodstream could in theory come to be genotypically similar to those from an earlier time point [3].

However, do different sporozoites having the same genotype in fact act inconsistently by functioning as either tachysporozoites or bradysporozoites [3]? Perhaps they do.

If not, then numerous (more than meets the eye) non-reinfection homologous recurrences of P. vivax malaria will obviously be recrudescences (clonal merozoite origin), not relapses [4].

Future research involving plasmodial sporozoites [5] will hopefully contribute to providing the answer to the question posed in the title of this blog.



1. Markus MB. The hypnozoite concept, with particular reference to malaria. Parasitol. Res. 2011;108(1):247–252.

2. Markus MB. Terms for coccidian merozoites. Ann. Trop. Med. Parasitol. 1987;81(4):463.

3. Markus MB. Source of homologous parasites in recurrent Plasmodium vivax malaria. J. Infect. Dis. 2012;206(4):622–623.

4. Markus MB. Biological concepts in recurrent Plasmodium vivax malaria. Parasitology. 2018;145(13):1765–1771.

5. Ruberto AA et al. Single-cell RNA sequencing of Plasmodium vivax sporozoites reveals stage- and species-specific transcriptomic signatures. bioRxiv Preprint. 2021 (posted 24 November).