Multiple causes of an unexpected malaria outbreak in a high-transmission area in Madagascar

Abstract

BackgroundThe malaria burden in Madagascar dropped down last decade, largely due to scale-up of control measures. Nevertheless, a significant rise of malaria cases occurred in 2011–2012 in two regions of the rainy South-Eastern Madagascar, where malaria is considered as mesoendemic and the population is supposed to be protected by its acquired immunity against Plasmodium. A multidisciplinary investigation was conducted in order to identify the causes of the outbreak.MethodsIn March 2012, a cross-sectional study was conducted in 20 randomly selected clusters, involving the rapid diagnostic testing of all ≥6 month-old members of households and a questionnaire about socio-demographic data and exposure to malaria control interventions. Changes in environmental conditions were evaluated by qualitative interview of local authorities, climatic conditions were evaluated by remote-sensing, and stock outs of malaria supplies in health facilities were evaluated by quantitative means. Two long-lasting insecticidal nets (LLINs) were sampled in each cluster in order to evaluate their condition and the remanence of their insecticidal activity. The entomological investigation also encompassed the collection Anopheles vectors in two sites, and the measure of their sensitivity to deltamethrin.ResultsThe cross-sectional survey included 1615 members of 440 households. The mean Plasmodium infection rate was 25.6 % and the mean bed net use on the day before survey was 71.1 %. The prevalence of Plasmodium infections was higher in 6–14 year-old children (odds ratio (OR) 7.73 [95 % CI 3.58–16.68]), in rural areas (OR 6.25 [4.46–8.76]), in poorest socio-economic tercile (OR 1.54 [1.13–2.08]), and it was lower in individuals sleeping regularly under the bed net (OR 0.51 [0.32–0.82]). Stock outs of anti-malarial drugs in the last 6 months have been reported in two third of health facilities. Rainfalls were increased as compared with the three previous rainy seasons. Vectors collected were sensitive to pyrethroids. Two years after distribution, nearly all LLINs collected showed a loss of physical integrity and insecticide activity,ConclusionsIncreased rainfall, decreasing use and reduced insecticide activity of long-lasting insecticide-treated nets, and drug shortages may have been responsible for, or contributed to, the outbreak observed in South-Eastern Madagascar in 2011–2012. Control interventions for malaria elimination must be sustained at the risk of triggering harmful epidemics, even in zones of high transmission.

Efficient method for establishing F1 progeny from wild populations of Anopheles mosquitoes

“…The malaria transmission pattern is currently changing in Madagascar with an epidemic situation for the past few years [20]. Among several other causes, there is suspicion of increased transmission by An.…”

Variation in Anopheles distribution and predictors of malaria infection risk across regions of Madagascar

“…In eastern humid tropical forest, Anopheles mosquitoes are more abundant in agricultural land and village environments than surrounding forests, indicating forest clearance as a possible driver of local malaria transmission (28). A cross-sectional study of communities in southeast Madagascar demonstrated that bed net use protected against malaria, while rural individuals in lower socioeconomic brackets, between 6-14 years of age, were at higher risk of infection (23,29). However, they did not collect information on malaria vector distribution, nor did they analyze these patterns in other regions.…”

Social vulnerability of children aged 5 to 15 years to malaria in Madagascar: 3 anthropological studies LLIN use

“…LLIN has made it possible to avoid more than 100,000 clinical cases of malaria each year [3]. In the southeast of Madagascar, the same author showed that nighttime LLIN use was signi cantly associated with lower parasite prevalence [4]. In areas with high LLIN coverage, people who do not sleep under a LLIN are at lower risk of malaria because of the reduction in overall malaria transmission in the area [5,6].…”

“…Another study in the east of the large island during a malaria epidemic (in late 2012) made a similar observation: the prevalence of Plasmodium falciparum infection was up to 8 times higher for 6-14-year-olds compared to those over 50 years old. However, the ratio was only 5.5 times higher for those under 5 years of age [4]. From 2016 to 2019, national data from the MinSanP suggest a gradual stabilization of malaria prevalence among children under 5 years of age but a continued increase in prevalence among children aged 6 to 13 years [12].…”