Trends in parasite prevalence following 13 years of malaria interventions on Bioko island, Equatorial Guinea: 2004–2016

Abstract

BackgroundWhilst there have been substantial reductions in malaria transmission over the past decade, in many countries in West and Central Africa the malaria burden remains high. Monitoring and evaluation of malaria transmission trends and intervention strategies are key elements for malaria control programmes. This study uses a time series of annual malaria indicator surveys to track the progress of malaria control in Bioko Island, Equatorial Guinea, over a 13 year period of intensive interventions. Malaria infection and haemoglobin were measured annually in children (1 to 14 years) in cross-sectional household surveys from 2004 to 2016 in 18 sentinel sites across the island. Trends in transmission patterns were assessed and the impact of the vector control interventions (net use and spray coverage) was evaluated.ResultsBetween 2004 and 2016 approximately 106,500 individual tests for parasitaemia were conducted using rapid diagnostic tests. Although spray coverage remained relatively high (> 70%) over the time period, reported net usage was generally below 40%. Parasite prevalence reduced from 43.3 to 10.5% between 2004 and 2016. The prevalence of moderate to severe anaemia in children aged 1–5 years reduced from 14.9 to 1.6%. Impact in individual sites ranged from 57 to 100% reductions in parasite prevalence between 2004 and 2016. Sleeping under a net and living in a house that had been sprayed in the past 12 months were independently protective against infection (OR = 0.69 [95%CI 0.61–0.80] and OR = 0.87 [95% CI 0.78–0.97], respectively), whilst recent travel to the mainland increased the odds of infection nearly fourfold (OR = 3.94 [95%CI 2.79–5.56]).ConclusionIsland-wide interventions have resulted in a substantial reduction in malaria transmission on Bioko Island. This unique time series of 13 consecutive annual malaria indicator surveys clearly demonstrates the long-term effectiveness of the sustained use of two vector control interventions, indoor residual spraying and LLINs, and the value of comprehensive and sustained surveillance. Despite considerable success in reducing the burden on the island, malaria is still endemic, with populations in some areas remaining at high risk of infection.Electronic supplementary materialThe online version of this article (10.1186/s12936-018-2213-9) contains supplementary material, which is available to authorized users.

Genetic polymorphism of Plasmodium falciparum circumsporozoite protein on Bioko Island, Equatorial Guinea and global comparative analysis

“…Malaria due to P. falciparum is a major public health problem on the island [16]. Since the Bioko Island Malaria Control Project (BIMCP) has launched at 2004, the parasite prevalence on Bioko decreased from over 45% prevalence in 2004 to 8.5% in 2016, and the reduction of entomological inoculation rate from more than 1,000 before 2004 to 14 in 2015 (www.mcdinternational.org).…”

Measuring the accuracy of gridded human population density surfaces: a case study in Bioko Island, Equatorial Guinea

“…While the population fractions were only several percentage points different between surfaces, on an island wide scale this represents several thousand potential malaria cases. Additionally, the range where we see the difference in results is around the mesoendemic to hypoendemic transmission threshold, which is where Bioko Island's parasite prevalence rate is currently estimated (21). Our results suggest the disparity in models is most apparent at these transition points between endemicity levels, which demonstrates the importance of using the most correct human population maps for modeling and estimating malaria.…”

Malaria outbreak in Riaba district, Bioko Island – Lessons learned

“…Second, the limited uptake of interventions by the population despite universal coverage may have also contributed to the problem. Data from annual MIS indicate that LLIN ownership and access constantly decrease from year to year, a problem that is ubiquitous across Bioko Island [1]. The last mass distribution campaign on Bioko took place in 2018, six months before the outbreak.…”