Deforestation and Industrial Agriculture Spur Zoonotic Diseases, Study Finds

A new study has iden­ti­fied a cor­re­la­tion between the loss of bio­di­ver­sity on the planet and the out­breaks of epi­demics, sug­gest­ing that defor­esta­tion and mono­cul­ture plan­ta­tions may favor the man­i­fes­ta­tion of zoonotic and vec­tor-borne dis­eases.

Reforestation that fails to repro­duce the pre­vi­ously exist­ing range of plant species can also lead to the same results, the study said.

On the other hand, palm oil plan­ta­tions are high­lighted as the type of sin­gle-crop farm­ing mainly respon­si­ble for the emer­gence of infec­tious dis­eases.

“Our results clearly sug­gest that it is not only for­est clear­ance that is respon­si­ble for out­breaks of infec­tious dis­eases but also refor­esta­tion or afforesta­tion, par­tic­u­larly in coun­tries out­side the trop­i­cal zone,” the authors of the study wrote.

A quar­ter of for­est loss is due to land-use changes to pro­duce cer­tain com­modi­ties, includ­ing beef, soy, palm oil and wood fiber. Mining oper­a­tions are also a fac­tor to con­sider when tack­ling for­est con­ver­sion, as they can affect var­i­ous oper­a­tions of the ecosys­tem like car­bon seques­tra­tion and soil regen­er­a­tion.

“We should take the costs of pub­lic health into account when con­sid­er­ing new plan­ta­tions or mines,” Serge Morand, a researcher at the French National Center for Scientific Research and one of the authors of the study, told The Guardian. ​“The risks are first to local peo­ple, but then world­wide because we have seen with Covid-19 how quickly dis­eases can spread.”

The study, pub­lished in Frontiers in Veterinary Science, is the first to exam­ine the asso­ci­a­tion between the loss of for­est cover and dis­ease out­breaks glob­ally. It spanned 26 years, from 1990 to 2016, and ana­lyzed thou­sands of cases of zoonotic and vec­tor-borne ail­ments emerg­ing in many coun­tries of the trop­i­cal and tem­per­ate zones.

The sci­en­tists derived data on global for­est cover from the World Bank, palm oil plan­ta­tions from the Food and Agricultural Organization of the United Nations and data on human infec­tious dis­eases from the GIDEON epi­demic data­base.

Then, they used gen­eral addi­tive mod­el­ing tech­niques to com­bine the derived data with pop­u­la­tion demo­graph­ics, con­clud­ing that there has been an increase of zoonotic dis­eases in defor­ested areas over time. In advance, com­mer­cial farm­ing, par­tic­u­larly the rapid expan­sion of palm tree plan­ta­tions, was found to have a pos­i­tive asso­ci­a­tion with increased vec­tor-borne dis­ease out­breaks.

Palm oil pro­duc­tion, how­ever, has been deemed unsus­tain­able by sev­eral coun­tries world­wide, which led to trad­ing lim­i­ta­tions of the prod­uct and the destruc­tion of palm tree plan­ta­tions in Sri Lanka.

The mech­a­nism behind the out­breaks lies in the oper­a­tion of the for­est envi­ron­ment itself, the researchers explained; a healthy, bio­di­verse for­est has the means to con­trol viruses and the emer­gence of dis­eases through a range of habi­tats and spe­cial­ized preda­tors.

In the case that the for­est is replaced by soy fields or palm tree plan­ta­tions, how­ever, the preda­tors van­ish and the ​“eco­log­i­cal reg­u­la­tion” is lost, allow­ing pathogen hosts such as mos­qui­toes and rats to spread dis­eases.

“I was sur­prised by how clear the pat­tern was,” Morand said. ​“We must give more con­sid­er­a­tion to the role of the for­est in human health, ani­mal health and envi­ron­men­tal health. The mes­sage from this study is don’t for­get the for­est.”

To fur­ther sup­port their results and pro­vide some sci­en­tific evi­dence of causal­ity, the researchers exam­ined indi­vid­ual case stud­ies on the change of land use and the man­i­fes­ta­tion of epi­demics.

They found that in South America, sev­eral stud­ies sug­gest that defor­esta­tion has spawned malaria epi­demics. In West Africa, sci­en­tific research has demon­strated that for­est clear­ing is the main dri­ver for the emer­gence of Ebola.

In tem­per­ate coun­tries, the emer­gence of dis­eases was mainly linked to refor­esta­tion. In Italy, the increased cases of tick-borne encephali­tis in humans are attrib­uted to small tick-host­ing mam­mals that thrive in cop­pice forests. In the United States, refor­esta­tion has led to increased deer pop­u­la­tions and the reap­pear­ance of tick-borne dis­eases.

“What is needed is a bet­ter way to stop both the loss of bio­di­verse native forests and a bet­ter man­age­ment of afforesta­tion to increase their con­tri­bu­tion not only to bio­di­ver­sity or car­bon seques­tra­tion but to local liveli­hood and health,” the researchers wrote.

“Scientists, pub­lic health and pol­i­cy­mak­ers should rec­on­cile the need to pre­serve bio­di­ver­sity while tak­ing into account the health risks posed by lack or mis­man­age­ment of for­est,” they added.

Morand finally warned that it is only a mat­ter of time for an epi­demic to become the next pan­demic.

“The risks are very high,” he con­cluded. ​”It’s just a case of when and where. We need to pre­pare.”

• Frontiers in Veterinary Science
• The Guardian