The world's scientific and social network for malaria professionals
Subscribe to free Newsletter | 10491 malaria professionals are enjoying the free benefits of MalariaWorld today

Relapsing Malaria and Parasite Numbers

June 17, 2020 - 01:16 -- Miles Markus

Only a "few" hypnozoites occur in patients who have Plasmodium vivax infections, compared to the large, non-circulating merozoite biomass that is now known to be present.

Therefore, to readily ascribe P. vivax malarial recurrences to hypnozoite activation, as is currently common practice, is no longer appropriate without good reasons for doing so. Forget about what you were taught at university in this context and keep an open mind.

It must now be assumed that as regards non-circulating parasite sources of recurrent P. vivax malaria, there is both (unless proved otherwise in the future) a hypnozoite and a merozoite origin – the latter certainly in early recurrences, probably. Thus, some recurrences will be relapses, whereas others will be recrudescences that have a non-bloodstream, tissue merozoite origin.

The bottom line is that recurrence of P.vivax malaria is partly a poorly understood, extravascular/sequestered parasite numbers-associated phenomenon. Hypnozoites are very much in the minority (ref. the first paragraph above).

For further information, see:

https://www.semanticscholar.org/paper/Biological-concepts-in-recurrent-Plasmodium-vivax-Markus/03c84f86a951b605fe389843b14dea4b84329d3f/figure/0

https://doi.org/10.1016/j.pt.2018.08.010

https://doi.org/10.1016/j.pt.2019.08.009

Comments

Submitted by Miles Markus on

What parasite stages are killed by dual drug treatment of P. vivax malaria (e.g. primaquine + chloroquine or tafenoquine + chloroquine); and where, exactly, does killing take place? In particular, what is the synergistic effect? Does more happen as a result of combination drug therapy than meets the eye? See the analysis in the 3rd reference (at the end of the above blog).

Submitted by Miles Markus on

It has been concluded from an interesting pioneering study (reference provided below) that in Plasmodium vivax infections, parasites are always present in the bone marrow.

I regard this as further evidence that the partly hypnozoite-independent Plasmodium vivax recurrence postulation (explained in the papers listed at the end of the above blog) is likely to be correct.

REFERENCE: Brito, M.A.M. et al. 2020. Morphological and transcriptional changes in human bone marrow during natural Plasmodium vivax malaria infections. Journal of Infectious Diseases (in press).