High heterogeneity in Plasmodium falciparum risk illustrates the need for detailed mapping to guide resource allocation: a new malaria risk map of the Lao People's Democratic Republic

Abstract

BackgroundAccurate information on the geographical distribution of malaria is important for efficient resource allocation. The Lao People's Democratic Republic has experienced a major decline in malaria morbidity and mortality in the past decade. However, efforts to respond effectively to these changes have been impeded by lack of detailed data on malaria distribution. In 2008, a countrywide survey on Plasmodium falciparum diagnosed in health centres and villages was initiated to develop a detailed P. falciparum risk map with the aim to identify priority areas for malaria control, estimate population at risk, and guide resource allocation in the Lao People's Democratic Republic.MethodsP. falciparum incidence data were collected from point-referenced villages and health centres for the period 2006-2008 during a country-wide survey between December 2008 and January 2009. Using the highest recorded annual rate, continuous surfaces of P. falciparum incidence were produced by the inverse distance weighted interpolation technique.ResultsIncidence rates were obtained from 3,876 villages and 685 health centres. The risk map shows that P. falciparum is highly heterogeneous in the northern and central regions of the country with large areas of no transmission. In the southern part, transmission is pervasive and the risk of P. falciparum is high. It was estimated that 3.4 million people (60% of the population) live at risk of malaria.ConclusionsThis paper presents the first comprehensive malaria risk map of the Lao People's Democratic Republic based entirely on empirical data. The estimated population at risk is substantially lower than previous estimates, reflecting the presence of vast areas with focal or no malaria transmission as identified in this study. These findings provide important guidance for malaria control interventions in the Lao People's Democratic Republic, and underline the need for detailed data on malaria to accurately predict risk in countries with heterogeneous transmission.

Vector Biology and Malaria Transmission in Southeast Asia

“…The monitoring of the susceptibility status of Anopheles to insecticides should be performed regularly as this provides essential information for the correct choice of insecticide to be most effective in vector control. Most studies suggest that ITNs can provide a fair degree of protection if properly used [66,63,67,68,69]. Therefore, Cambodia has actively distributed ITNs to many at-risk populations.…”

“…A field survey for malaria prevalence in southern Laos using molecular-based parasite detection assay showed that mixed species infections were common with all 4 human plas-modia species detected among 23.1% of positive samples [82]. A recent national survey of the malaria distribution revealed that approximately 41% of the country's population is living in areas of no malaria transmission, particularly large areas in the central regions of the country while malaria incidence of more than 1 per 1,000 population is occurring in seven provinces, Saravane, Savannakhet, Sekong, Attapeu, Champasack, Khammouan, Phongsaly, collectively representing 36% of the Lao population [3,69]. Significant reductions have been reported following investments in malaria control, in particular the large-scale introduction of artemi sinin-based combination therapy (ACT) beginning in 2004, ITNs introduced in 2000, and IRS in 2010, in conjunction with socio-economic and environmental changes [3].…”

“…Volunteers are selected by villagers and a village committee to provide primary health care services, including diagnosis and management of respiratory diseases, diarrhea, and uncomplicated malaria. Activities also include performing health education, assist in vaccination campaigns, and report morbidity and mortality data to the local health center or the district health office [69]. In Laos, insecticideimpregnated bednets have been reported to reduce malaria transmission successfully [68].…”

Future malaria spatial pattern based on the potential global warming impact in South and Southeast Asia

“…The main findings from the use of this map showed that Plasmodium falciparum dominated spatially in the northern and central regions of the country, while large areas did not have any transmission; the areas in which transmission and risk were high were in the southern regions. Additionally, 60% of the population was found to be at risk of contracting malaria (Jorgensen et al, 2010). In China, the central-south counties of Hainan had the highest malaria incidences with 75% of cases recorded during May and October and a positive correlation between cases and climatic factors such as temperature (Xiao et al, 2010).…”

“…With respect to the geographical distribution of malaria in southern and southeastern Asia, a few studies illustrate the spatial or spatiotemporal risk distribution of malaria or its vectors and link the distribution with the current climatic factor values or economic resources. For instance, in Lao People's Democratic Republic (Lao PDR), a detailed P. falciparum risk map was developed and used to identify populations at risk and to guide resource allocation for the ultimate purpose of malarial control (Jorgensen et al, 2010). The main findings from the use of this map showed that Plasmodium falciparum dominated spatially in the northern and central regions of the country, while large areas did not have any transmission; the areas in which transmission and risk were high were in the southern regions.…”