Persistent Non -Falciparum Malaria in Kenya: Evidence from 17 Years of Sentinel Surveillance

Background Human malaria is caused by several Plasmodium species, including P. falciparum, P. malariae, P. ovalecurtisi, P. ovalewallikeri, P. vivax, and P. knowlesi. Pf is the most virulent and the primary target of most interventions, although mixed-species infections are common. Non-falciparum species are more difficult to diagnose, treat, control, and eliminate. This study aimed to determine the burden of Plasmodium species among symptomatic individuals in selected regions of Kenya. Materials and Methods Between 2008 and 2025, a total of 4,255 blood samples were collected from symptomatic individuals presenting at healthcare facilities across 7 sentinel sites, namely, Busia, Kericho, Kisii, Kisumu, Kombewa, Malindi, and Marigat, and were analyzed for species composition via qPCR. Results Plasmodium falciparum was dominant in 4,139/4,255 (97.3% 95% CI 0.96-0.97), followed by P. ovalewallikeri 545/4,255 (12.8% 95% CI 0.11-0.13), P. malariae 235/4,255 (5.5% 95% CI 0.04-0.06), and P. ovalecurtisi 217/4,255 (5.1% 95% CI 0.04-0.05). Up to 3,460/4,255 (81.3%) were single-species infections. Between 2008 and 2025, P. falciparum remained the dominant species across all study sites, while mixed infections involving Plasmodium malariae, Plasmodium ovalecurtisi, and Plasmodium ovalewallikeri occurred intermittently at varying frequencies, indicating sustained transmission of non-falciparum species. The geographic distribution of Plasmodium single-species and mixed-species varied significantly across surveillance sites (x2 P = .000) with the Lake endemic region showing the greatest species diversity. Conclusions Although Plasmodium falciparum remained the predominant species among symptomatic individuals, non-falciparum parasites, including Plasmodium malariae, Plasmodium ovalecurtisi, and Plasmodium ovalewallikeri, were consistently detected. The occurrence of mixed infections indicates persistent but low-level transmission of these species. These findings underscore the importance of sensitive multi-species diagnostic and surveillance approaches to better inform malaria control and elimination strategies.