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Deforestation linked to changes in spread of infectious diseases

Deforestation and land use changes impact the spread of infectious diseases, research suggests.

Deforestation in Malaysia
Forest loss in Borneo. (C) Joshua Paul for LSHTM.

In Malaysian Borneo, deforestation has been linked to increases in human cases of Plasmodium knowlesi, a type of malaria carried by macaques and spread to people through bites by infected mosquitoes.

Scientists have exploited a combination of satellite and epidemiological field study data to look how environmental factors such as changes in forest cover influence disease risks. They used machine learning approaches to identify how areas of forest loss was linked to the number of cases of this type of malaria in people in certain areas in Borneo.

Their findings suggest that areas that have been cleared and left without forest, within 1km from people’s homes, are strongly associated with risk of disease. This was also observed in areas at 4-5 km where there has been forest loss.

The reason why this happens is unclear but it seems that these environmental changes affect the numbers and location of people, mosquitoes and macaques. Researchers suggest that macaques may move distances of up to 5 km in response to deforestation, exposing people living and working in those areas.

Prediction of disease risk

Mapping infectious diseases plays a vital role in guiding public health policy and practice. This work shows that models that include environmental factors evaluated at different scales can better predict disease risks than models which simply evaluate a single scale. This approach can be used to understand how environment shapes disease risk and to identify high risk areas, including for other vector-borne diseases of public health concern.

This painstaking analysis of the role of spatial scale in determining the impact of deforestation and forest loss on predictions of P. knowlesi malaria incidence in Borneo, showed that identifying the right scale for each risk factor made the model work better at predicting disease risk. This information will be invaluable for helping us understand the processes that drive P. knowlesi malaria transmission to humans, and is an approach that could be helpful for many other diseases.

Professor Rowland Kao, The Roslin Institute

The work of this international collaboration, which has been led by Paddy Brock at the University of  Glasgow and Kim Fornace of the London School of Hygiene and Tropical Medicine, is published in the journal “Royal Society Proceedings B” and has been funded by the Medical Research Council.

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