Submicroscopic Plasmodium falciparum gametocyte carriage is common in an area of low and seasonal transmission in Tanzania

Abstract

Summaryobjective: Recently developed molecular gametocyte detection techniques have shown that submicroscopic Plasmodium falciparum gametocytes are common in symptomatic patients and can infect mosquitoes. The relevance for the infectious reservoir of malaria in the general population remains unknown. In this study, we investigated submicroscopic asexual parasitaemia and gametocytaemia in inhabitants of an area of hypoendemic and seasonal malaria in Tanzania.methods: Two cross-sectional malariometric surveys were conducted in the dry and wet seasons of 2005 in villages in lower Moshi, Tanzania. Finger prick blood samples were taken to determine the prevalence of P. falciparum parasites by microscopy, rapid diagnostic test and real-time nucleic acid sequence-based amplification (QT-NASBA).results: 2752 individuals participated in the surveys, of whom 1.9% (51/2721) had microscopically confirmed asexual parasites and 0.4% (10/2721) had gametocytes. In contrast, QT-NASBA revealed that 32.5% (147/453) of the individuals harboured asexual parasites and 15.0% (68/453) had gametocytes. No age dependency or seasonality was observed in submicroscopic parasite carriage.discussion: Molecular detection techniques reveal that carriage of submicroscopic asexual parasite and gametocyte densities is relatively common in this low transmission area. Submicroscopic gametocytaemia is likely to be responsible for maintaining malarial transmission in the study area.

Plasmodium falciparum gametocyte carriage, sex ratios and asexual parasite rates in Nigerian children before and after a treatment protocol policy change instituting the use of artemisinin-based combination therapies

“…Although gametocyte carriage rates are now lower after consistent and widespread use of ACTs in patients with acute malaria, these relatively low rates are likely to be underestimated due to significant submicroscopical gametocytaemia. The submicroscopical gametocytaemia in children from this and other endemic areas (Shekalaghe et al 2007, Happi et al 2009, Ouédraogo et al 2009) is detectable by polymerase chain reaction (PCR) and may substantially contribute to the gametocyte reservoir.…”

“…The main limitations of the present study are as follows: symptomatic individuals were employed in the evaluation of the various gametocyte carriage rates, the various gametocyte carriage rates are likely to be underestimated since submicroscopic gametocytaemia detectable by PCR is not uncommon in children from endemic areas (Shekalaghe et al 2007, Happi et al 2009) and may contribute substantially to transmission, and gametocyte sex was determined morphologically, instead of using PCR, a more accurate method of gametocyte sex determination (Drew & Reece 2007). In addition, gametocyte viability and infectivity to mosquito before and after policy change was not evaluated.…”

Biology of Malaria Transmission

“…Although mature gametocyte presence in the blood has long been thought to be crucial for an efficient transmission, these stages were rarely detected by microscopy (Dowling and Shute 1966;Bejon et al 2006) and, therefore, it was previously assumed that only a small proportion of malaria-infected individuals carried gametocytes. With the use of sensitive molecular assays, it is now clear that gametocytes are present in most malaria infections and at highly variable densities (Schneider et al 2007;Shekalaghe et al 2007) that can successfully infect mosquitoes (Schneider et al 2007;Bousema et al 2012;Churcher et al 2013). Given the highly variable and nonlinear relationship between gametocyte density and mosquito infection rate (Bousema et al 2012;Churcher et al 2013), quantifying the human component of the infectious reservoir is a challenging task.…”

Influence of Anemia on Plasmodium falciparum Gametocyte Sex Ratios in Acutely Symptomatic Children

“…This would suggest anemia predisposes these children to gametocyte carriage and supports finding from others areas of Africa and elsewhere [5,23]. Submicroscopic gametocytaemia, detectable by polymerase chain reaction (PCR), is not uncommon in children undergoing antimalarial therapy [11,24]. Therefore, our overall estimates of gametocyte carriage in anemic and non-anemic children are likely to be underestimates.…”