Disturbed habitats can promote the spread of tropical disease

When night falls in Panama’s forests, the time of the opossums begins. The marsupials, which have spent the day sleeping in trees, climb down the trunks and search for fruit, frogs or eggs on the ground. The omnivores often carry a hazardous parasite—the Chagas disease pathogen.

A new study by Ulm University published in the journal One Health has now shown that the more humans intervene in nature, the more host animals are infected with Trypanosoma cruzi, and the more the tropical disease spreads.

The study analyzes small mammals in various habitats: from pristine rainforests to commercial timber plantations. The research provides new insights into how land use and changes in biodiversity can contribute to the spread of zoonotic pathogens.

Chagas disease is caused by the single-celled parasite Trypanosoma cruzi. The main vectors are blood-sucking predatory bugs, which usually pass on the pathogen via feces or urine when they bite humans or animals in search of blood meals. In addition to humans, more than 180 wild and domestic animal species can serve as hosts, which makes combating the disease particularly difficult.

According to the World Health Organization, 6 to 7 million people are infected worldwide, with about 75 million people living in risk areas—mainly in Latin America. If left untreated, the infection can lead to severe heart or digestive problems, which can be life-threatening.

Although there are drugs that are effective in the early stages of the disease, there is no vaccine. The disease is currently spreading—favored by climate change, which is creating new environmental conditions in which the predatory bug can establish itself as a vector.

“Our results show how human influence affects the diversity of wild animals—and how the loss of biodiversity changes the dynamics of pathogens,” says first author Dr. Magdalena Meyer from the Institute of Evolutionary Ecology and Conversation Genomics at Ulm University.

For their study, the researchers examined more than 800 small mammals at 23 locations in a region around the Panama Canal—in pristine rainforests, on protected islands, in fragmented forest patches and in teak monocultures.

Opossums are spreading—and increasing the risk of infection

The researchers found that the composition of the wildlife communities changed. In disturbed habitats, it was primarily the adaptable opossums that prevailed. Because the marsupials are particularly susceptible hosts, the Chagas pathogen also benefited from this.

“The reinforced spread of opossums increases the hazard of the pathogen jumping to livestock, pets or humans,” explains Dr. Meyer. At the same time, the scientists observed that the genetic diversity of another host species—the spiny rat—decreases in disturbed habitats. This also favors the spread of the pathogen.

The results of the study have direct implications for health protection: millions of people worldwide are affected by Chagas disease, particularly disadvantaged population groups in Latin America. However, this neglected tropical disease receives little international attention.

“Our research impressively shows how closely human, animal and environmental health are linked within the meaning of the One Health approach,” emphasizes study leader Professor Simone Sommer. “The best protection against the spread of such diseases is the preservation of intact ecosystems with their natural biodiversity.”