Changing Clinical Epidemiology of Plasmodium vivax Malaria as Transmission Decreases: Population-Based Prospective Panel Survey in the Brazilian Amazon

Changing Clinical Epidemiology of Plasmodium vivax Malaria as Transmission Decreases: Population-Based Prospective Panel Survey in the Brazilian Amazon

Abstract Background Malarial infections are often missed by microscopy, and most parasite carriers are asymptomatic in low-endemicity settings. Whether parasite detectability and its ability to elicit symptoms change as transmission declines remains unclear. Methods We performed a prospective panel...

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Published in:The Journal of infectious diseases Vol. 229; no. 4; pp. 947 - 958
Main Authors: Fontoura, Pablo S, Macedo, Evelyn G, Calil, Priscila R, Corder, Rodrigo M, Rodrigues, Priscila T, Tonini, Juliana, Esquivel, Fabiana D, Ladeia, Winni A, Fernandes, Anderson R J, Johansen, Igor C, Silva, Marcos F, Fernandes, Amanda O S, Ladeia-Andrade, Simone, Castro, Marcia C, Ferreira, Marcelo U
Format: Journal Article
Language:English
Published: US Oxford University Press 12-04-2024
Subjects:
Asymptomatic
Disease transmission
Epidemiology
Infections
Malaria
Medical diagnosis
Microscopy
Parasites
Peripheral blood
Plasmodium vivax
Surveys
Brazil
Amazon Basin
clinical expression
microscopy
Amazon
molecular diagnosis
Plasmodium vivax
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Summary:Abstract Background Malarial infections are often missed by microscopy, and most parasite carriers are asymptomatic in low-endemicity settings. Whether parasite detectability and its ability to elicit symptoms change as transmission declines remains unclear. Methods We performed a prospective panel survey with repeated measurements on the same participants over 12 months to investigate whether Plasmodium vivax detectability by microscopy and risk of symptoms upon infection varied during a community-wide larviciding intervention in the Amazon basin of Brazil that markedly reduced vector density. We screened 1096 to 1400 residents in the intervention site for malaria by microscopy and quantitative TaqMan assays at baseline and twice during intervention. Results We found that more P vivax infections than expected from their parasite densities measured by TaqMan assays were missed by microscopy as transmission decreased. At lower transmission, study participants appeared to tolerate higher P vivax loads without developing symptoms. We hypothesize that changes in the ratio between circulating parasites and those that accumulate in the bone marrow and spleen, by avoiding peripheral blood microscopy detection, account for decreased parasite detectability and lower risk of symptoms under low transmission. Conclusions P vivax infections are more likely to be subpatent and remain asymptomatic as malaria transmission decreases. Plasmodium vivax detectability by microscopy and its ability to elicit symptoms decrease as transmission is reduced in the Amazon. Changes in the ratio between circulating parasites and those accumulating in the bone marrow and spleen might account for this finding.
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ISSN:0022-1899
1537-6613
DOI:10.1093/infdis/jiad456