Identifying individual, household and environmental risk factors for malaria infection on Bioko Island to inform interventions

Abstract

Background Since 2004, malaria transmission on Bioko Island has declined significantly as a result of the scaling-up of control interventions. The aim of eliminating malaria from the Island remains elusive, however, underscoring the need to adapt control to the local context. Understanding the factors driving the risk of malaria infection is critical to inform optimal suits of interventions in this adaptive approach. Methods This study used individual and household-level data from the 2015 and 2018 annual malaria indicator surveys on Bioko Island, as well as remotely-sensed environmental data in multilevel logistic regression models to quantify the odds of malaria infection. The analyses were stratified by urban and rural settings and by survey year. Results Malaria prevalence was higher in 10–14-year-old children and similar between female and male individuals. After adjusting for demographic factors and other covariates, many of the variables investigated showed no significant association with malaria infection. The factor most strongly associated was history of travel to mainland Equatorial Guinea (mEG), which increased the odds significantly both in urban and rural settings (people who travelled had 4 times the odds of infection). Sleeping under a long-lasting insecticidal net decreased significantly the odds of malaria across urban and rural settings and survey years (net users had around 30% less odds of infection), highlighting their contribution to malaria control on the Island. Improved housing conditions indicated some protection, though this was not consistent across settings and survey year. Conclusions Malaria risk on Bioko Island is heterogeneous and determined by a combination of factors interacting with local mosquito ecology. These interactions grant further investigation in order to better adapt control according to need. The single most important risk factor identified was travel to mEG, in line with previous investigations, and represents a great challenge for the success of malaria control on the Island.

Assessing IRS performance in a gender-integrated vector control programme on Bioko Island, Equatorial Guinea, 2010–2021

“…Indoor residual spraying takes place in houses across Bioko Island, the largest island of Equatorial Guinea with an area of about 2000 km 2 . The population is urban, with 85% of the island’s 270,000 inhabitants living in the capital of Malabo [ 16 ]. Malaria is endemic with perennial transmission on Bioko; before project implementation the Plasmodium falciparum parasite rate was 45% in 2–14 year-old children and has since declined by about 75% [ 16 ].…”

GIS-based spatiotemporal mapping of malaria prevalence and exploration of environmental inequalities

“…Malaria prevalence in Nigeria differs across geopolitical regions because of the varying environmental and seasonal settings that affect the reproductive patterns of mosquito vectors. The prevalence of malaria is primarily a function of its underlying transmission intensity (Alegana et al 2013 ), which in turn is propelled by indicators such as interventions (García et al 2023 ), environmental and climatic factors (Ekpa et al 2023 ; Rivera and Gutiérrez 2023 ), and socio-economic and demographic characteristics (Ogunsakin and Chen 2020 ; Pourtois et al 2023 ; Rivera and Gutiérrez 2023 ). In malaria prevalence research, authors have linked malaria rates to environmental and socio-economic factors like population density and potential evapotranspiration (PET) (Yang et al 2012 , 2005 ).…”

A cross-sectional study to ascertain malaria prevalence among asymptomatic travellers arriving on the Lihir Group of Islands, Papua New Guinea: implications for elimination efforts

“…Travellers are common sources of imported malaria. For instance, a prevalence survey in the low-burden island of Bioko, Equatorial Guinea, showed that malaria infection was highly related with having a history of travel to mainland Equatorial Guinea [ 11 ]. In PNG, the haplotypes of P. vivax isolates from different regions revealed patterns of transmission following major human migration routes, especially within the ‘Islands region’ of PNG [ 12 ].…”