Characterizing microscopic and submicroscopic malaria parasitaemia at three sites with varied transmission intensity in Uganda

Abstract

BackgroundParasite prevalence is a key metric used to quantify the burden of malaria and assess the impact of control strategies. Most published estimates of parasite prevalence are based on microscopy and likely underestimate true prevalence.MethodsThick smear microscopy was performed in cohorts of children (aged 6 month to 10 years) and adults every 90 days over 2 years, at three sites of varying transmission intensity in Uganda. Microscopy-negative samples were tested for sub-microscopic parasitaemia using loop-mediated isothermal amplification (LAMP). Generalized estimating equation models were used to evaluate associations between age and parasitaemia, factors associated with sub-microscopic infection and associations between parasitaemia and haemoglobin.ResultsA total of 9260 samples were collected from 1245 participants. Parasite prevalence among children across the three sites was 7.4, 9.4 and 28.8 % by microscopy and 21.3, 31.8 and 69.0 % by microscopy plus LAMP. Parasite prevalence among adults across the three sites was 3.1, 3.0 and 5.2 % by microscopy and 18.8, 24.2 and 53.5 % by microscopy plus LAMP. Among those with parasitaemia, adults and persons recently treated with anti-malarial therapy had the highest prevalence of sub-microscopic infection. Children with sub-microscopic or microscopic parasitaemia had lower mean haemoglobin levels compared to children with no detectable parasites.ConclusionsAcross a range of transmission intensities in Uganda, microscopy vastly underestimated parasite prevalence, especially among adults.

Low prevalence of laboratory-confirmed malaria in clinically diagnosed adult women from the Wakiso district of Uganda

“…The survey also uncovered six to tenfold higher rates of parasitaemia using a combination of LM and molecular techniques, highlighting high levels of previously unappreciated sub-microscopic parasitaemia [8]. In this study asymptomatic women did not have parasitaemia detectable by RDT, LM or PCR, implying that malaria rates may be low in the population.…”

“…A 2011–2013 community-based survey conducted in three Ugandan sub-counties with varied transmission settings performed the first rigorous assessment of malaria metrics in both children and adults [7–9]. According to the results of this survey, malaria prevalence based on LM ranged from 3.0 to 5.1% among adults aged ≥18, while prevalence based on both LM and molecular techniques ranged from 18.8 to 53.5% in the same age group [8]. This is one of the first detailed studies on the prevalence of malaria in adults, but additional data from other regions and broad age groups is needed to adequately monitor malaria trends in Uganda [10].…”

Evidence of strain structure in Plasmodium falciparum var gene repertoires in children from Gabon, West Africa

“…The DBLα domain is present in all var genes except the atypical, placental adhesion VAR2CSA. Typical of high transmission areas in West Africa, asymptomatic infections represent the majority of the P. falciparum parasite population across all age groups (28)(29)(30). While carrying parasites most of the time, children experience only one to five clinical episodes per year with 1-2% of these infections leading to severe clinical disease (31).…”

Marked variation in prevalence of malaria-protective human genetic polymorphisms across Uganda

“…Out of the 1,344 subjects enrolled, 44% were children under 5 years of age, 32% 5–10 years, and 24% above 18 years. Prior reports defined malaria transmission, prevalence, and incidence in the three cohorts, as summarized in Table 1 (Kamya et al, 2015; Rek et al, 2016). The sites differed markedly, with very high transmission intensity, parasite prevalence, and malaria incidence in Tororo District, lower levels of all of these parameters in Kanungu District, and the lowest levels in Jinja District.…”

“…To establish the cohorts, all households within the three sub-counties were enumerated and mapped, and randomly selected households that included at least one resident 0.5–10 years of age and one adult resident were enrolled, as previously described (Kamya et al, 2015). This study included cohort members reported previously and additional subjects recruited into the cohorts after prior reports (Kamya et al, 2015; Rek et al, 2016). Cohort household adults provided the primary language spoken by the household.…”