Epidemiology of forest malaria in central Vietnam: a large scale cross-sectional survey

Abstract

In Vietnam, a large proportion of all malaria cases and deaths occurs in the central mountainous and forested part of the country. Indeed, forest malaria, despite intensive control activities, is still a major problem which raises several questions about its dynamics.A large-scale malaria morbidity survey to measure malaria endemicity and identify important risk factors was carried out in 43 villages situated in a forested area of Ninh Thuan province, south central Vietnam. Four thousand three hundred and six randomly selected individuals, aged 10–60 years, participated in the survey. Rag Lays (86%), traditionally living in the forest and practising "slash and burn" cultivation represented the most common ethnic group. The overall parasite rate was 13.3% (range [0–42.3] while Plasmodium falciparum seroprevalence was 25.5% (range [2.1–75.6]). Mapping of these two variables showed a patchy distribution, suggesting that risk factors other than remoteness and forest proximity modulated the human-vector interactions. This was confirmed by the results of the multivariate-adjusted analysis, showing that forest work was a significant risk factor for malaria infection, further increased by staying in the forest overnight (OR= 2.86; 95%CI [1.62; 5.07]). Rag Lays had a higher risk of malaria infection, which inversely related to education level and socio-economic status. Women were less at risk than men (OR = 0.71; 95%CI [0.59; 0.86]), a possible consequence of different behaviour. This study confirms that malaria endemicity is still relatively high in this area and that the dynamics of transmission is constantly modulated by the behaviour of both humans and vectors. A well-targeted intervention reducing the "vector/forest worker" interaction, based on long-lasting insecticidal material, could be appropriate in this environment.

Low perception of malaria risk among the Ra-glai ethnic minority in south-central Vietnam: implications for forest malaria control

“…Malaria control is based on early diagnosis and treatment with artemisinin-based combination therapy and the provision of insecticide-treated nets (ITNs), distributed free-of-charge and insecticide-treated twice a year by the national malaria control programme. Reported ITN use in the study area was high (86.3%, in April 2004) with a median coverage of 2.5 people per bed net [12]. Similar to other forested areas of central Vietnam, despite intensive efforts, malaria remains difficult to control due to the complex interactions between humans, vectors and environmental factors [4].…”

“…Today, the Ra-glai are a largely impoverished ethnic minority in Vietnam, almost exclusively dedicated to small-scale subsistence slash and burn agriculture in fields located in the surrounding forests. According to a survey carried out in 2003, 80% of the active population can be categorized as 'forest worker', 99.5% of which participate in slash and burn agriculture, occasionally combined with hunting, gathering of forest products and logging [12]. The Ra-glai's heavy dependence on the forest for subsistence activities places them at greater risk for malaria infection, a risk that is further increased by staying overnight in the forest [12,17].…”

“…According to a survey carried out in 2003, 80% of the active population can be categorized as 'forest worker', 99.5% of which participate in slash and burn agriculture, occasionally combined with hunting, gathering of forest products and logging [12]. The Ra-glai's heavy dependence on the forest for subsistence activities places them at greater risk for malaria infection, a risk that is further increased by staying overnight in the forest [12,17]. Indeed the main malaria vector Anopheles dirus sensu stricto , is a sylvatic and highly anthropophilic species, resting mainly outdoors and biting early in the evening [18].…”

Epidemiology of forest malaria in Central Vietnam: the hidden parasite reservoir

“…Asymptomatic malaria infections are common in remote and forested areas of Central Vietnam [5-7], particularly among local ethnic minorities in which the burden of Plasmodium vivax is particularly high. A recent survey carried out in Ninh Thuan Province (Central-Southern Vietnam), in which filter paper blood samples were analysed by molecular techniques, showed the presence of a largely hidden human reservoir of malaria infections with numerous sub-patent infections (detected only by PCR but not by microscopy) including mixed infections with Plasmodium malariae and Plasmodium ovale [8].…”

Socioeconomic inequities in the health and nutrition of children in low/middle income countries

“…Recently, several large-scale cross-sectional surveys show higher frequencies of malaria infection among the poor in Asia and Africa. 21,32,35,45 In the vast majority of DHS and MICS, caretakers of poor children reported that diarrhea prevalence among poor children was 30% or more than the rate in the top quintile ( Figure 7 and Table 2). Similar results were obtained in 20 out of the 26 MICS countries with such information (webtable 3.17).…”