Risk factors for malaria infection and transmission in Burkina Faso, an area of high, persistent malaria transmission and high insecticide resistance

Abstract

Malaria remains a public health problem despite the large decline in infection and disease between 2000 and 2015, due largely to the massive deployment of insecticide-treated nets (ITN). Recent years have been marked, however, by a stagnation in progress in high burden countries. In 2020, the World Health Organisation (WHO) reported that the key targets of WHO’s global malaria strategy have been missed. The 11 high burden high impact countries (10 in sub-Saharan Africa including Burkina Faso, plus India) accounted for approximately 70% or more of the world’s malaria case burden and 71% of global estimated deaths from malaria in 2020. About 253 million ITNs have been distributed in malaria endemic countries in 2019 with an increase of 56 million ITNs compared with 2018. Approximatively 84% of these ITNs were delivered to countries in sub-Saharan Africa. In parallel, the WHO global malaria 2020 report on insecticide resistance on malaria vectors highlights resistance to the four common insecticide classes (pyrethroids, organochlorines, carbamates, organophosphates) in 74 out the of the 82 endemic countries. The resistance to pyrethroids, the only insecticide class currently used in ITNs continues to be widespread in all major malaria vectors across malaria endemic countries.
Burkina Faso is one of the few countries not to have shown an association between ITN ownership and a reduction in child mortality. Artemisinin-based combination therapy (ACT) and Intermittent Preventive Treatment of Malaria in pregnant women using sulfadoxine-pyrimethamine (IPTp-SP) was introduced in 2006, ITNs have been distributed free of charge since 2010 every three years and seasonal malaria chemoprevention (SMC) in children under five years has been scaled up across the country in 2016. Following the mass distribution of more than 30 million ITNs in 2010, 2013, 2016 and 2019, more than 97% of households owned at least one ITN, although estimates of the proportion of children sleeping under an ITN range from <30% in the dry season to >70% in the peak transmission season. Despite the high coverage, cases of malaria remain high with 380 cases per 1000 in 2015, 536 cases per 1000 in 2017 and 528 cases per 1000 in 2018. Reasons for the lack of effectiveness of ITNs may include the high levels of insecticide resistance in malaria vectors, incomplete coverage of ITNs, poor condition of the nets and whether people use them correctly.
Here I explored the risk factors for malaria in Burkina Faso, mainly in children and pregnant women and for indoor densities of malaria mosquitoes. This thesis hypothesised that malaria in Burkina Faso was less common among children and pregnant women living in modern housing and with high socio-economic status.
Two epidemiological study models (cohort study and cross-sectional survey) were implemented to help determine major risk factors for Plasmodium falciparum infection in an area of persistent and intense malaria transmission in rural Burkina Faso, with high ITN coverage and high levels of insecticide resistance, throughout different population groups (children, pregnant women and all age population).
Incidence of P. falciparum infection remains overwhelmingly high in the study area with school-age children at greatest risk. Caregivers with high socio-economic status (odds ratio, OR =1.05, 95% CI 1.00 - 1.11, p=0.04), having travelled out of the study area (OR=1.52, 95% CI 1.45 - 1.52, p<0.001), or being literate (OR=1.71, 95% CI 1.26 - 2.32, p=0.001), were at increased risk. Conversely, sleeping in a metal-roofed house (OR=0.6, 95% CI 0.4 - 1.0, p=0.03) and having an electricity supply in the child’s bedroom (OR=0.4, 95% CI 0.3 - 0.7, p=0.001), reduced the risk of house entry by Anopheles gambiae, the dominant malaria vectors in the study area.
During pregnancy there was a reduced risk of P. falciparum infection associated with the use of ITNs (Odds ratio, OR=0.31, 95% CI 0.12–0.79, p=0.02), while this association was not found in the general population or among children. In pregnant women, increasing the dose of IPTp-SP, was associated with the reducing the odds of infection by 40% (OR=0.59, 95% CI 0.43–0.81, p<0.001).
The study findings suggest that malaria control in Burkina Faso and other countries in sub-Saharan Africa experiencing persistently high malaria transmission need additional interventions to contribute to accelerate the disease burden reduce and to achieve the goals of WHO global strategies by 2030. My findings highlight the potential of improved housing to reduce malaria transmission as further opportunities for improving malaria control.