Medical Science Research Bulletin

Background: Malaria control programmes have traditionally focused on symptomatic infections, yet individuals who harbour parasites without current symptoms may sustain transmission while remaining outside routine case-detection pathways. The epidemiology of asymptomatic malaria in Benue South, North-Central Nigeria, remains insufficiently characterized. 

Objectives: This study assessed the prevalence of asymptomatic malaria parasitaemia among apparently healthy community dwellers and compared parasite detection by rapid diagnostic testing (RDT) and light microscopy. 

Methods: A community-based cross-sectional study was conducted between August and October 2024 among apparently healthy residents aged ≥15 years in selected rural and semi-urban communities of Otukpo and Okpokwu Local Government Areas (LGAs), Benue State, Nigeria. Participants were selected using a multistage sampling approach. Information on socio-demographic characteristics, malaria prevention practices, healthcare access and selected environmental exposures was obtained using a structured questionnaire. Venous blood samples were examined using malaria RDTs and Giemsa-stained thick and thin blood films. Parasite density was estimated using the standard white-cell-count assumption. Descriptive statistics were used to summarize the study population and diagnostic findings.

Results: A total of 275 participants were studied; 123 (44.73%) were male and 152 (55.27%) females. The largest age group was 15–29 years (107; 38.91%). Microscopy detected malaria parasitaemia in 88 participants, corresponding to a prevalence of 32.0% (95% CI 26.5–37.5%), whereas RDT detected infection in 55 participants, corresponding to 20.0% (95% CI 15.3–24.7%). Thus, microscopy identified 12 percentage points more positive participants than RDT, with a descriptive prevalence ratio of 1.60. Among microscopy-positive participants, 74/88 (84.09%) had parasite densities below 1,000 parasites/µL, while 14/88 (15.91%) had densities ≥1,000 parasites/µL. Malaria prevention information had reached 72.0% of participants, while 53.82% reported always using insecticide-treated nets. Stagnant water was reported near the homes of 64.0% of participants. 

Conclusion: A substantial proportion of apparently healthy residents of Otukpo and Okpokwu LGAs harboured microscopically detectable malaria parasites. The higher proportion detected by microscopy than RDT highlights the importance of maintaining quality-assured microscopy capacity for community surveillance, particularly where parasite densities may be low. The findings support continued investment in vector control, community-level prevention and surveillance approaches that recognize asymptomatic infection as part of the malaria reservoir.

asymptomatic malaria, parasitaemia, malaria prevalence, microscopy, rapid diagnostic test, parasite density, Benue State, Nigeria.

1. World Health Organization. World malaria report 2025. Geneva: World Health Organization; 2025.
2. World Health Organization. WHO guidelines for malaria. Geneva: World Health Organization; 2025.
3. World Health Organization. WHO guidelines for malaria: 30 November 2024. Geneva: World Health Organization; 2024.
4. Research Malaria Microscopy Standards Working Group. Microscopy for the detection, identification and quantification of malaria parasites on stained thick and thin blood films in research settings. Geneva: World Health Organization; 2015.
5. World Health Organization. Malaria microscopy quality assurance manual. 2nd ed. Geneva: World Health Organization; 2016.
6. World Health Organization. Microscopy examination of thick and thin blood films for identification of malaria parasites: malaria microscopy standard operating procedure 08. Geneva: World Health Organization; 2016.
7. World Health Organization. Malaria parasite counting: malaria microscopy standard operating procedure 09. Geneva: World Health Organization; 2016.
8. Bousema T, Okell L, Felger I, Drakeley C. Asymptomatic malaria infections: detectability, transmissibility and public health relevance. Nat Rev Microbiol. 2014;12(12):833–840. doi:10.1038/nrmicro3364.
9. Lindblade KA, Steinhardt L, Samuels A, Kachur SP, Slutsker L. The silent threat: asymptomatic parasitemia and malaria transmission. Expert Rev Anti Infect Ther. 2013;11(6):623–639. doi:10.1586/eri.13.45.
10. Okell LC, Ghani AC, Lyons E, Drakeley CJ. Submicroscopic infection in Plasmodium falciparum-endemic populations: a systematic review and meta-analysis. J Infect Dis. 2009;200(10):1509–1517. doi:10.1086/644781.
11. Okell LC, Bousema T, Griffin JT, Ouedraogo AL, Bousema T, Ghani AC. Factors determining the occurrence of submicroscopic malaria infections and their relevance for control. Nat Commun. 2012;3:1237. doi:10.1038/ncomms2241.
12. Wu L, van den Hoogen LL, Slater H, Walker PGT, Ghani AC, Drakeley CJ, et al. Comparison of diagnostics for the detection of asymptomatic Plasmodium falciparum infections to inform control and elimination strategies. Nature. 2015;528(7580)–S93. doi:10.1038/nature16039.
13. Ouédraogo AL, Gonçalves BP, Gnémé A, Wenger EA, Guelbeogo MW, Ouédraogo A, et al. Dynamics of the human infectious reservoir for malaria determined by mosquito feeding assays and ultrasensitive malaria diagnosis in Burkina Faso. J Infect Dis. 2016;213(1):90–99. doi:10.1093/infdis/jiv370.
14. Gonçalves BP, Kapulu MC, Kabaria C, Guelbeogo WM, Drakeley C, Bousema T, et al. Examining the human infectious reservoir for Plasmodium falciparum malaria in areas of differing transmission intensity. Nat Commun. 2017;8:1133. doi:10.1038/s41467-017-01270-y.
15. Njama-Meya D, Kamya MR, Dorsey G. Asymptomatic parasitaemia as a risk factor for symptomatic malaria in a cohort of Ugandan children. Trop Med Int Health. 2004;9(8):862–868. doi:10.1111/j.1365-3156.2004.01277.x.
16. Staalsoe T, Hviid L. The role of variant-specific immunity in asymptomatic malaria infections: maintaining a fine balance. Parasitol Today. 1998;14(5):177–178. doi:10.1016/S0169-4758(98)01228-9.
17. Hviid L. Clinical disease, immunity and protection against Plasmodium falciparum malaria in populations living in endemic areas. Expert Rev Mol Med. 1998;1998:1–10. doi:10.1017/S1462399498000179.
18. Färnert A, Arez AP, Correia AT, Björkman A, Snounou G, do Rosário VE. Sampling and storage of blood and the detection of malaria parasites by polymerase chain reaction. Trans R Soc Trop Med Hyg. 1999;93(1):50–53. doi:10.1016/S0035-9203(99)90177-3.
19. Greenwood BM. Progress in malaria control in endemic areas. Travel Med Infect Dis. 2008;6(4):173–176. doi:10.1016/j.tmaid.2007.11.003.
20. Greenwood BM. Control to elimination: implications for malaria research. Trends Parasitol. 2008;24(10):449–454. doi:10.1016/j.pt.2008.07.002.
21. Ibrahim AO, Bello IS, Ajetunmobi AO, Ayodapo A, Afolabi BA, Adeniyi MA. Prevalence of asymptomatic malaria infection by microscopy and its determinants among residents of Ido-Ekiti, Southwestern Nigeria. PLoS One. 2023;18(2). doi:10.1371/journal.pone.0280981.
22. Aju-Ameh C, Awolola S, Mwansat G, Mafuyai H. Prevalence of asymptomatic malaria in selected communities in Benue State, North Central Nigeria: a silent threat to the national elimination goal. Edorium J Epidemiol. 2017;3:1–7. doi:10.5348/E06-2017-3-OA-1.
23. Nwaneli EI, Eguonu I, Ebenebe JC, Osuorah CDI, Ofiaeli OC, Nri-Ezedi CA. Malaria prevalence and its sociodemographic determinants in febrile children: a hospital-based study in a developing community in South-East Nigeria. J Prev Med Hyg. 2020;61(2)–E180. doi:10.15167/2421-4248/jpmh2020.61.2.1350.
24. Kaghou MM, Metoh TN, Fru CT, Berinyui S, Bindamu M, Chi A, et al. High prevalence and risk factors associated with asymptomatic malaria among children in Nkwen village, Northwest Region, Cameroon. Malar J. 2024;23:243. doi:10.1186/s12936-024-05013-x.
25. Telfils R, Dossou AY, Djènontin A, Adimi E, Akoho R, Bailly J, et al. Dynamics of submicroscopic and microscopic asymptomatic malaria infection and associated factors: a longitudinal study in South Benin. PLoS One. 2024;19(12). doi:10.1371/journal.pone.0311217.
26. Bastiaens GJH, Bousema T, Leslie T. Scale-up of malaria rapid diagnostic tests and artemisinin-based combination therapy: challenges and perspectives in sub-Saharan Africa. PLoS Med. 2014;11(1). doi:10.1371/journal.pmed.1001590.
27. Drakeley CJ, Gonçalves BP, Okell LC, Bousema T. Human infectious reservoir and malaria transmission: implications for elimination. In: malERA research agenda publications. PLoS Med. 2017;14(7). doi:10.1371/journal.pmed.1002452.
28. Soumaré HM, Blanken SL, Ahmad A, Ooko M, Gaye PM, Jadama L, et al. Asymptomatic school children and adults are important for the human infectious reservoir for Plasmodium falciparum malaria in an area of low endemicity in The Gambia. J Infect. 2025;91(1):106507. doi:10.1016/j.jinf.2025.106507.