Asymptomatic Plasmodium vivax malaria in the Brazilian Amazon: Submicroscopic parasitemic blood infects Nyssorhynchus darlingi.

Gregório Guilherme Almeida,Mauro Shugiro Tada,Joseph Michael Vinetz,Marcia Caldas De Castro,Maria Marta Figueiredo,Maísa Da Silva Araujo,Lis Ribeiro Do Valle Antonelli,Alex Fiorini Carvalho,Irene Da Silva Soares,Douglas Taylor Golenbock,Dhelio Batista Pereira,Gabriela Ribeiro Gomes,Jansen Fernandes Medeiros,Luzia Helena Carvalho,Flora Satiko Kano,Pedro Augusto Carvalho Costa,Ricardo Tostes Gazzinelli,Photini Sinnis

doi:10.1371/journal.pntd.0009077

Abstract

Individuals with asymptomatic infection due to Plasmodium vivax are posited to be important reservoirs of malaria transmission in endemic regions. Here we studied a cohort of P. vivax malaria patients in a suburban area in the Brazilian Amazon. Overall 1,120 individuals were screened for P. vivax infection and 108 (9.6%) had parasitemia detected by qPCR but not by microscopy. Asymptomatic individuals had higher levels of antibodies against P. vivax and similar hematological and biochemical parameters compared to uninfected controls. Blood from asymptomatic individuals with very low parasitemia transmitted P. vivax to the main local vector, Nyssorhynchus darlingi. Lower mosquito infectivity rates were observed when blood from asymptomatic individuals was used in the membrane feeding assay. While blood from symptomatic patients infected 43.4% (199/458) of the mosquitoes, blood from asymptomatic infected 2.5% (43/1,719). However, several asymptomatic individuals maintained parasitemia for several weeks indicating their potential role as an infectious reservoir. These results suggest that asymptomatic individuals are an important source of malaria parasites and Science and Technology for Vaccines granted by Conselho Nacional de may contribute to the transmission of P. vivax in low-endemicity areas of malaria.

Highlights

Plasmodium vivax is spread worldwide and it is frequently considered to be low pathogenic, it is an important cause of morbidity and mortality in endemic areas in central and south America, and in regions of Asia and Oceania [1,2]
The advance of molecular diagnosis brought to light the existence of asymptomatic infections, which may represent most of the infections in some areas
We describe the general characteristics of asymptomatic individuals infected with Plasmodium vivax, and provide evidence of their potential as parasitic reservoirs, even when molecular methods fail to detect the infection

Summary

Introduction

Plasmodium vivax is spread worldwide and it is frequently considered to be low pathogenic, it is an important cause of morbidity and mortality in endemic areas in central and south America, and in regions of Asia and Oceania [1,2]. The annual incidence of vivax malaria has reduced since the last century in Brazil, but to achieve elimination new strategies are needed to optimize diagnostic and early treatment, and to block transmission from humans to mosquitoes [3]. Asymptomatic (ASY) cases of P. vivax infection are mostly undetectable, neglected, and remain untreated. For this reason, asymptomatic malaria require active surveillance and poses as one of the most challenging obstacles for the control of Plasmodium infections worldwide [6,7]. The role of these submicroscopic infections in the maintenance of endemicity is not well understood, it is generally thought that they may serve as parasitic reservoirs sustaining endemicity and causing new outbreaks [9,10,11]

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Discussion

Conclusion