Seroprevalence and parasite rates of Plasmodium malariae in a high malaria transmission setting of southern Nigeria.

While Plasmodium falciparum continues to be the main target for malaria elimination, other Plasmodium species persist in Africa. Their clinical diagnosis is uncommon while rapid diagnostic tests (RDTs), the most widely used malaria diagnostic tool, are only able to distinguish between P. falciparum and non-falciparum species, the latter as pan-species. Blood samples, both from clinical cases and communites, were collected in southern Nigeria (Lagos and Calabar) in 2017 (October-December) and 2018 (October-November), and analysed by several methods, namely microscopy, quantitative real-time PCR (qPCR), and peptide serology targeting candidate antigens (PmAMA1, PmLDH and PmCSP). The sensitivity of the diagnostic approaches for the dominant P. falciparum were comparable, detecting approx. 80% infection, but not so for non-falciparum species - 3% and 10% infection for P. malariae; 0% and 3% infection for P. ovale by microscopy and qPCR respectively, across communities. P. ovale prevalence was less than 5%. Infection rates for P. malariae varied between age groups, with the highest rates in individuals > 5 years. P. malariae specific seroprevalence rates fluctuated in those < 10 years but generally reached the peak around 20 years of age for all peptides. The heterogeneity and rates of these non-falciparum species calls for increased specific diagnosis and targeting by elimination strategies.