The Relative Contribution of Symptomatic and Asymptomatic Plasmodium vivax and Plasmodium falciparum Infections to the Infectious Reservoir in a Low-Endemic Setting in Ethiopia

Abstract

Background. Te majority of Plasmodium vivax and Plasmodium falciparum infections in low-endemic settings are asymptomatic. Te relative contribution to the infectious reservoir of these infections compared to clinical malaria cases is currently unknown. Methods. We assessed infectivity of passively recruited symptomatic malaria patients (n = 41) and community-recruited asymptomatic individuals with microscopy-detected (n = 41) and polymerase chain reaction (PCR)-detected infections (n = 82) using membrane feeding assays with Anopheles arabiensis mosquitoes in Adama, Ethiopia. Malaria incidence and prevalence data were used to estimate the contributions of these populations to the infectious reservoir. Results. Overall, 34.9% (29/83) of P. vivax- A nd 15.1% (8/53) P. falciparum-infected individuals infected =1 mosquitoes. Mosquito infection rates were strongly correlated with asexual parasite density for P. vivax (p = 0.63; P < .001). Adjusting for population prevalence, symptomatic, asymptomatic microscopy-detected, and PCR-detected infections were responsible for 8.0%, 76.2%, and 15.8% of the infectious reservoir for P. vivax, respectively. For P. falciparum, mosquito infections were sparser and also predominantly from asymptomatic infections. Conclusions. In this low-endemic setting aiming for malaria elimination, asymptomatic infections were highly prevalent and responsible for the majority of onward mosquito infections. Te early identifcation and treatment of asymptomatic infections might accelerate elimination efforts.