Deforestation's effects on malaria rates vary by time and distance


Date:
March 9, 2021
Source:
eLife
Summary:
Deforestation may cause an initial increase in malaria infections
across Southeast Asia before leading to later decreases, a study
suggests.



FULL STORY ========================================================================== Deforestation may cause an initial increase in malaria infections across Southeast Asia before leading to later decreases, a study published
today in eLife suggests.


==========================================================================
The results may help malaria control programs in the region develop
better strategies for eliminating malaria infections and educating
residents on how to protect themselves from infection.

Mosquitos spread the malaria parasite to humans causing infections that
can be severe and sometimes deadly. In the area along the Mekong river
in Southeast Asia, many residents hunt or harvest wood in the surrounding forests, which can increase their risk of infection. Yet recent outbreaks
of malaria in the region have also been linked to deforestation.

"As countries in the region focus their malaria control and elimination
efforts on reducing forest-related transmission, understanding the
impact of deforestation on malaria rates is essential," says first
author Francois Rerolle, Graduate Student Researcher at the University
of California San Francisco (UCSF), US, who works within the UCSF Malaria Elimination Initiative.

To better understand the effects of deforestation on malaria transmission, Rerolle and colleagues examined both forest cover data and village-level malaria incidence data from 2013-2016 in two regions within the Greater
Mekong Sub-region.

They found that in the first two years following deforestation activities, malaria infections increased in villages in the area, but then decreased
in later years. This trend was mostly driven by infections with the
malaria parasite Plasmodium falciparum. Deforestation in the immediate 1-10-kilometer radius surrounding villages did not affect malaria rates,
but deforestation in a wider 30-kilometer radius around the villages
did. The authors say this is likely due to the effect that wider
deforestation can have on human behaviour.

"We suspect that people making longer and deeper trips into the forest
results in increased exposure to mosquitoes, putting forest-goers at
risk," Rerolle explains.

Previously, studies on the Amazon in South America have found increased
malaria infections in the first 6-8 years after deforestation, after
which malaria rates fall. The difference in timing may be due to regional differences. The previous studies in the Amazon looked at deforestation
driven by non-indigenous people moving deeper into the forest, while communities in the current study have long lived at the forest edges
and rely on subsistence agriculture.

"Our work provides a more complete picture of the nuanced effects of deforestation on malaria infections," says senior author Adam Bennett,
Program Lead at the UCSF Malaria Elimination Initiative. "It may
encourage more in- depth studies on the environmental and behavioural
drivers of malaria to help inform strategies for disease elimination." ========================================================================== Story Source: Materials provided by eLife. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Francois Rerolle, Emily Dantzer, Andrew A Lover, John M Marshall,
Bouasy
Hongvanthong, Hugh JW Sturrock, Adam Bennett. Spatio-temporal
associations between deforestation and malaria incidence in Lao PDR.

eLife, 2021; 10 DOI: 10.7554/eLife.56974 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/03/210309132543.htm

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