Farming and forest loss: study exposes malaria’s best friends

A new study exposes the role of deforestation in amplifying malaria transmission, finding that forest loss and malaria is linked worldwide and not just a local phenomenon. The research, published in Environmental Science, builds on prior evidence that has linked deforestation to an increase in habitat availability for mosquitoes in several malaria-endemic countries throughout the tropics.

Despite assurances by the World Health Organisation (WHO) that malaria incidence has declined by 60 percent globally in the last 15 years, the disease still claimed around 450,000 lives in 2015 alone – one of the largest causes of death in the developing world and an ongoing threat to the health of half of the world’s population. Meanwhile, numbers from the UN Food and Agriculture Organization (FAO) indicate nearly 130 million hectares of forest have been lost globally since 1990 – an area about the size of South Africa.

“There was a lack of research on whether [the connection between deforestation and malaria] was a general trend or whether these findings were unique to certain settings, influenced by nuances of local ecology,” said Kelly Austin of Lehigh University, a lead researcher of the study. “I was interested in seeing if the relationship between deforestation and malaria could be generalised across nations or regions.”

Using a research technique that maps complex relationships between ecological and social outcomes known as structural equation modelling, Austin and her team assessed the connection between forest loss and malaria prevalence across 67 countries. The first study of its kind to compare trends between nations rather than observations at individual sites, it found that the deforestation and malaria connection was unmistakable and rife in every region considered. In places with the severest deforestation, there were more recorded cases of malaria – and more deaths associated with them. Indeed, deforestation was a more potent predictor of malaria prevalence than a country’s distance from the equator.

“My findings speak to the difficulties we will face in trying to manage malaria in the years to come,” she said. “The changes that humans are making to the natural environment are creating conditions that are favourable to mosquitoes and larvae development.”

Although often mistaken as the prime suspect in malaria, mosquitoes only act as accomplices by harboring the agent responsible for malaria – Plasmodium falciparum – a microscopic, single-celled organism that is transferred to human hosts via the bite of a female Anopheles mosquito. When temperatures drop below 16 degrees Celsius (60 degrees Fahrenheit), the parasite becomes weak and dies, confining malaria to the planet’s lower latitudes.

By clearing forests in these areas, humans create additional opportunities for most mosquito species to breed and proliferate, including Anopheles mosquitoes. Felling trees strips the land of shade and removes a vital store of moisture, allowing water to pool and be heated by direct sunlight, providing ideal conditions for breeding mosquitoes. Destroying forests also robs many animals of their home – some of which might ordinarily prey on mosquitoes. Fewer birds and mammals and more mosquitoes also means a greater proportion of the disease is concentrated in human rather than animal hosts.

Intensifying climate change and habitat loss “could slow or impede progress” tackling malaria noted Austin.

Perhaps unsurprisingly, countries with poorer public health conditions – fewer doctors, limited access to clean water and low levels of secondary education – were also likely to suffer a heavier malaria burden. Such countries were overwhelmingly likely to be poorer on average, while richer nations with more robust medical infrastructure had less to fear from the illness.

Like the standing water that spawns the disease, malaria-crippled economies are often stagnant. The cost of prevention and treatment can exhaust public finances while lost productivity starves the revenue needed to repay it. Malaria-endemic countries are overwhelmingly represented in the lowest three quartiles of income classification, marking them among the poorest and most deprived places on Earth.

A seemingly obvious solution would be to accelerate economic development in these places – easing poverty and its deadly interaction with malaria for millions of people. Many initiatives designed by richer governments and international organizations have deployed this kind of thinking. But, given the link between malaria and deforestation, Austin warns against the “off-shoring of environmental degradation” that is inherent in development policy that simply prioritizes food production. The study noted that countries with greater specialization in agriculture and larger rural populations had higher rates of forest loss – and therefore higher rates of malaria infection.

“Deforestation is concentrated in developing nations due to larger socio-economic forces, including a dependence on agricultural production that is often driven by demand from affluent nations like the United States. In this way, our consumption habits are connected to malaria prevalence in the Global South,” she argued, adding that “There are a handful of crops that account for a disproportionate amount of deforestation globally, including beef, soybeans, coffee, and palm oil… commodities that we can live without or consume far less of.”

Global action on malaria is coordinated in part by The Roll Back Malaria Partnership (RBMP) formed in 1998 between WHO and the UN. The scheme’s extended title gives some idea of its prescription for the health pandemic: “Roll Back Malaria, Roll In Development.” But is malaria policy keeping pace with the discovery of its link to deforestation?

Dr. Daddi J. Wayessa, a manager at RBMP, argues yes and points to a focus on “sustainable development,” which he claims does not create a “receptive environment” for malaria but which encourages ideas and input from a diverse range of people.

“Environmental change has a tremendous impact on malaria transmission,” Wayessa said. “The findings of this study are the recognition of the need for a multi-sector approach, which is the core principle of RBM – to bring together all actors.”

Researchers from the study argue that the disease consequences of environmental change are complicated, and therefore demand nuanced responses. Among the lessons for addressing the symptoms of the problem is targeted help for communities on the “front lines” of forest loss, they write, including the distribution of mosquito nets and other preventative measures that can assist people living and working near major deforestation sites.

“Leaving just a few trees could make a big difference in water absorption,” Austin said.

Tackling the causes of deforestation will require more fundamental change. Making a forceful case for public autonomy over forests, pressuring foreign businesses to responsibly source produce and investing in education and alternative livelihoods for frontline communities should all be prioritized by aid agencies and governments who pledge to eradicate malaria, Austin argued.

“A huge step would be for governments and companies from affluent nations to practice more sustainable approaches in their production sites abroad,” she said. “There needs to be global enforcement that is consistent across nations, so it’s not so easy for companies to move dirty or environmentally-demanding industries to less developed nations that have lax regulations and lack the ability for enforcement.”

Header image: The sun sets on boggy former forest in Riau, Indonesia – model habitat for malaria-bearing mosquitoes.

CITATIONS

Austin, K. F., Bellinger, M. O. & Rana, P. (2017). Anthropogenic forest loss and malaria prevalence: a comparative examination of the causes and disease consequences of deforestation in developing nations. Environmental Science, 11(2), 217-231.

Bi, Y. & Shilu, T. (2014). Poverty and malaria in the Yunnan province, China. Infectious Diseases of Poverty, 3(1), 32.

Roll Back Malaria Partnership Secretariat. (2011). Economic costs of malaria. World Health Organization. Available from: URL: http://www. rbm. who. int/cmc_upload/0/000/015/363/RBMInfosheet_10. htm.

Santos-Vega, M., Bouma, M. J., Kohli, V. & Pascual, M. (2016). Population density, climate variables and poverty synergistically structure spatial risk in urban malaria in India. PLoS neglected tropical diseases, 10(12), 51-55.