High prevalence of Plasmodium malariae from hospital and communities in a high malaria transmission setting of Southern Nigeria

Background: Plasmodium malariae is one of five malaria parasite species prevalent across sub-Saharan Africa, but with limited data on its prevalence and epidemiology across most endemic settings. Specific clinical diagnosis of P. malariae and other non-falciparum malaria parasites is uncommon and the most widely used malaria diagnostic tool, rapid diagnostic tests (RDTs), predominantly targets P. falciparum while nonspecifically identifying co-infecting species as pan-species. Moreover, undetectable submicroscopic infections of these non-falciparum infections are likely and constitute a reservoir that could sustain transmission and challenge the achievement of elimination goals. This study aimed to explore prevalence of P. malariae infections in a high malaria transmission setting in Nigeria. Methods: A preliminary survey was first carried out in two sites to compare prevalence of non-falciparum species in southern Nigeria, results of which informed subsequent sample collection. Study participants were recruited from health facilities in Lagos and Calabar between October to December 2017 and subsequently from health facilities in four communities in Akpabuyo local government area of Cross River State, Nigeria from October to November 2018, following community sensitization and consent. Pan species RDT (SD Bioline, Cat No 05FK60) was used for field diagnosis and Thick blood films were also collected for microscopic detection of malaria parasites. Dried blood spots (DBS) collected from all participants were used for molecular detection of Plasmodium species by real-time PCR techniques. Results: Plasmodium falciparum was most prevalent in the study populations, 22 to 48% of all samples tested. From the primary survey, significantly higher prevalence of P. malariae and P. ovale were detected by qPCR in Calabar compared to Lagos. From a resampling of communities in Calabar, (N=798), Plasmodium spp infection prevalence by RDT was 23%. Non-falciparum infections detected was 12.5%, of which a median prevalence of 10.3% were infections with P. malariae (mixed and mono). The distribution of P. malariae infections between age groups (7.3 to 16.1%) and communities (6.2 to 12.1%) was heterogeneous. 32.9% of P. malariae infections occurred in the 11-15yrs age bracket, mostly as mixed infections. The odds of P. malariae as a mono infection was highest in the 0-5yrs age group relative to the group with the least odds of mono infections (11-15yrs). P. ovale was detected at 2.3%, while no sample tested positive for P. vivax. Conclusions: Overall, P. malariae was the most prevalent non-falciparum species and occurred mostly in the 11-15yrs age group, who are not targeted by some elimination strategies. Approaches for routine diagnosis of non-falciparum species in endemic settings will facilitate interventions towards pan-species malaria elimination. Keywords: Plasmodium malariae, malaria control, elimination, non-falciparum, sub-Saharan Africa