Epidemiology of Relapsing and Falciparum Malaria in the Highlands of Cameroon: An Integrated Community Survey of Human Infection and Vector Abundance

Despite global malaria control efforts, the disease caused 263 million cases and 597,000 deaths in 2023. While Plasmodium falciparum accounts for most cases in Africa, non-falciparum species, such as P. ovale spp. and P. vivax, can cause relapse infections and are increasingly recognized as significant contributors to human disease. In particular, the highlands of West Cameroon have previously been reported to have high P. vivax infection rates. This study presents preliminary results from the Relapsing Malaria in Africa (ReMA) study, conducted in Dschang, Cameroon, to assess the prevalence and epidemiology of P. vivax and P. ovale. A cross-sectional survey of 3,661 participants from 871 households across seven health areas identified a low prevalence of P. vivax (0.1%) and P. ovale spp. (0.64%) using quantitative real time PCR (qPCR), while P. falciparum remained prevalent at 8.1%. Co-infections of P. ovale spp. with P. falciparum were observed in 23.1% of P. ovale spp. cases. While gametocytemia was common among falciparum infections, leveraging a new ovale gametocyte assay, we found that gametocytemia was uncommon among the qPCR-positive ovale infections. Spatial analysis found P. vivax and P. ovale spp. infections concentrated in Penka-Michel and Baleveng, the former having higher Anopheles spp. abundance than other areas assessed. Risk factor analysis revealed children and those with recent domestic travel had higher odds of P. falciparum infection, but no significant associations were found for P. ovale spp. infections. Entomological surveys confirmed high densities of Anopheles gambiae sensu lato (s.l.) and An. funestus (s.l.), with significantly higher human landing capture rates for An. gambiae s.l compared to other mosquito species. While these findings suggest that the relapsing malarias are not as widespread as previously thought in West Cameroon, understanding factors driving their persistent transmission, especially without prevalent gametocytemia, will be important for disease control. AUTHOR SUMMARYMalaria caused 263 million cases and 597,000 deaths in 2023, with most cases in Africa due to Plasmodium falciparum. However, the dangers of other species like P. ovale and P. vivax, which can cause relapsing infections, are becoming more clear in Africa. The Relapsing Malaria in Africa (ReMA) study in Dschang, Cameroon, surveyed 3,661 people from 871 households to better understand these infections. Results showed low rates of P. vivax (0.1%) and P. ovale (0.64%) compared to P. falciparum (8.1%). Infections were more common in areas with high mosquito abundance and biting activity. While the relapsing malarias were less common than expected, understanding factors driving their persistent transmission, especially without prevalent gametocytemia, will be important for disease control.