Deforestation inhibits malaria transmission in Lao PDR: a spatial epidemiology using Earth observation satellites

Abstract

Background: The present study aimed to analyze the impact of deforestation on the malaria distribution in the Lao People's Democratic Republic (Lao PDR), with consideration of climate change.

Methods: Malaria distribution data from 2002 to 2015 were obtained from the Ministry of Health of Lao PDR and each indicator was calculated. Earth observation satellite data (forested area, land surface temperature, and precipitation) were obtained from the Japan Aerospace Exploration Agency (JAXA). Structured equation modeling (SEM) was conducted to clarify the relationship between the malaria incidence and Earth observation satellite data.

Results: As a result, SEM identified two factors that were independently associated with the malaria incidence: area and proportion of forest. Specifically, malaria was found to be more prevalent in the southern region, with the malaria incidence increasing as the percentage of forested land increased (both p < 0.01). With global warming steadily progressing, forested areas are expected to play an important role in the incidence of malaria in Lao PDR. This is believed because malaria in Lao PDR is mainly forest malaria transmitted by Anopheles dirus.

Conclusion: To accelerate the elimination of malaria in Lao PDR, it is important to identify, prevent, and intervene in places with increased forest coverage (e.g., plantations) and in low-temperature areas adjacent to malaria-endemic areas, where the vegetation is similar to that in malaria-endemic areas.

Keywords: Anopheles; Climate change; Deforestation; Global warming; Land use/land cover; Lao PDR; Malaria.

Fig. 1

Malaria index (API: annual parasite incidence per 1000 population at risk) in each district of Lao PDR in 2015. The map was constructed by the author based on the data provided by the Ministry of Health Lao PDR

Fig. 2

Deforestation in Champasak Province. In Champasak Province, 721.5 km² forest (8.4% of the province) disappeared from 1992 to 2015. This figure was constructed by the author based on European Space Agency (ESA) data (300 m resolution) and a forest map using ALOS/ALOS-2 (10 m resolution)

Fig. 3

LST and precipitation in each region of Lao PDR from 2002 to 2015. Out of high-temperature provinces, provinces other than the capital city are malaria-endemic area (southern region). This figure was constructed by author based on JAXA data [MODIS (JASMES), AMSR-E, ANSR-2]

Fig. 4

Transition of LST and precipitation in Champasak Province from 2002 to 2015. This figure was constructed by author based on JAXA data [MODIS (JASMES), AMSR-E, ANSR-2]

Fig. 5

Determinants of malaria incidence. Final model of the SEM constructed using data from each province for 2002 to 2015. CMIN/df = 1.252, CFI = 0.989, GFI = 0.989. ¹Southern region = 2, and the other regions except capital city = 1, ²API. ³Proportion of forested land was calculated based on European Space Agency (ESA) data. ⁴LST was based on National Aeronautics and Space Administration (NASA) data. ⁵Precipitation was also based on NASA data. *All correlations were statistically significant (p < 0.01)