A report is adding to the evidence that disruptions to an ecosystem caused by deforestation can help spread a bacterial pathogen.

Medical science is dealing with about 250 known human emerging infectious diseases, driven along by rapid urbanization in developing countries and human population encroachment in former wilderness areas.  One example is the Zika virus, because the mosquitoes that spread it thrive in artificial habitats created by humans, such as old cans, barrels, and tires that collect water and provide a breeding ground for the insects.

A study appearing in this month's edition of journal Science Advances says many of these emerging infectious diseases came from tropical rainforests - especially freshwater aquatic systems.  The authors examined deforestation and other land-use changes that caused the collapse of a freshwater food-web, leading to the increased prevalence of a bacterial pathogen called Mycobacterium ulcerans, which causes a skin disease in humans known as Buruli ulcer.  Patients often require surgery and skin grafting, and may still suffer long-term disability.

Looking at cases in French Guiana in South America, they found a pattern:  Man moves into a wilderness area, and cuts down the trees; the degraded environment hosts fewer predators at the top of the food chain; lower organisms that make better hosts for M. ulcerans are allowed to breed unchecked, creating more opportunities for humans to become infected.

The authors write:  "Because human populations have greater contact with land-use change generated by global urbanization, it is not unreasonable to predict that emergence and reemergence of infectious diseases will become more common." 

"We therefore recommend that more empirical evidence must be sought for mechanisms related to disease emergence in areas of anthropogenic disturbance, notably in tropical regions of the world where biodiversity (at both micro- and macroscales) can be high."