Predominance of asymptomatic and sub-microscopic infections characterizes the Plasmodium gametocyte reservoir in the Peruvian Amazon

Abstract

Malaria transmission requires that Anopheles mosquitoes ingest Plasmodium gametocyte stages circulating in the human bloodstream. In the context of malaria elimination, understanding the epidemiology of gametocytes relative to all Plasmodium infections and the contribution of asymptomatic and sub-microscopic parasite carriers to the gametocyte reservoir is necessary, especially in low endemic settings with predominance of P.vivax. A 13-month longitudinal study was conducted in two communities (n = 1935 individuals) of Loreto Department, Peru, with five active screenings for Plasmodium infections and gametocyte stages by quantitative real-time PCR (qPCR) and reverse transcription (RT)-qPCR, respectively. Parasite prevalence by qPCR was 7.2% for P.vivax (n = 520/7235; range by survey 6.0%-8.1%) and 3.2% for P.falciparum (n = 235/7235; range by survey 0.4%-7.7%). Sub-microscopic infections accounted for 73.5% of P.vivax (range by survey 60%-89%) and almost the totality of P.falciparum cases. Gametocytes were found in 28.4% P.vivax infections (range by survey 18.7%-34.1%), with a peak of 61.5% in one community at the start of the transmission season. About 59.8% of all P.vivax gametocyte carriers were asymptomatic and 31.9% were sub-microscopic. Age patterns for gametocyte prevalence paralleled asexual stage infections and peaked among >15–25 year old individuals. Asexual parasite density was found to be the strongest predictor for P.vivax gametocyte presence in longitudinal multivariate analysis (odds ratio 2.33 [95% confidence interval 1.96, 2.78]; P<0.001). Despite significant differences in seasonality patterns and P.vivax prevalence found at the local scale, sub-microscopic and asymptomatic infections predominate and contribute significantly to the gametocyte reservoir in different communities of the Peruvian Amazon. Control and elimination campaigns need sensitive tools to detect all infections that escape routine malaria surveillance, which may contribute to maintain transmission in the region.

Prevalence and Force of Plasmodium Vivax and Plasmodium Falciparum Blood Stage Infection and Associated Clinical Malaria Burden in the Brazilian Amazon

“…A higher prevalence of malaria infection in the rainy season was also shown in previous studies, corroborating what has already been described for other regions of the Amazon [34,35]. The predictors of P. vivax clinical disease found in our study were seasonality, and marginally, frequency of travel and use of mosquito nets.…”

“…Recent studies in the Amazon region and other malaria endemic areas in the world have shown a high proportion of submicroscopic P. vivax infections [7,17,34]. In the present study, factors associated with P. vivax positivity were age (20-60 years), seasonality, use of mosquito nets and IRS.…”

Guaroa Virus and Plasmodium vivax Co-Infections, Peruvian Amazon

“…These symptoms could, at least in part, have been related to the GROV infection consistent with other clinical symptom reports (3). Understanding the origin of symptoms in co-infected persons is further complicated because both asymptomatic malaria and arboviral disease are common (14,29).…”

Modern biological research of Plasmodium vivax malaria pathogen

“…Дослідження населення в ендемічних районах Колумбії, де P. vivax реєструється від 77,2% до 94,8% випадків, виявило 56% безсимптомних носіїв, що були інвазивними для лабораторних комарів Anopheles albimanus [20]. У таких пацієнтів за допомогою світлової мікроскопії збудники не діагностувались.…”