Biodiversity degradation may have perverse consequences for emerging pathogens

Habitat destruction and species extinction may lead to an increase in diseases that infect humans and other species, according to a paper in the journal Nature co-authored by a University of Florida ecologist.

In the paper to be published Thursday, UF biology professor Robert D. Holt and his colleagues reported that by reviewing studies from a wide range of systems, including data from plants, animals and bacteria, they were able to relate dimensions of environmental loss, and in particular species loss, with incidence of infectious disease. The study -- which was led by biologist Felicia Keesing of Bard College -- focused on diseases on the rise, such as West Nile virus, Lyme disease and Hantavirus.

"The general degradation of biodiversity because of land use transformation, combined with climate change, overharvesting, and so forth, is likely to have many perverse consequences for emerging pathogens," said Holt, a UF Eminent Scholar associated with the Emerging Pathogens Institute. "You have to think both as an ecologist and an infectious disease specialist to grapple with questions like this."

Some pathogens can flourish under less biologically diverse conditions, such as in areas where top predators or other key species become extinct.

To illustrate this point, the researchers use an example study of how a dwindling population of opossums in Virginia forests contributes to the spread of Lyme disease. Opossums are able to effectively kill disease-carrying ticks when the ticks attach to them, helping to limit the population of the parasite. When opossum populations decline, tick populations flourish and feed off the Virginia white-footed mouse, which is less able to defend itself from the blood-feeding ticks. In addition, the mouse's ability to reproduce quickly and in great numbers means there are more vulnerable hosts available. Species that are resilient to human impacts may often have correlated biological traits that permit them to be effective hosts of pathogens.

The area and spatial arrangement of natural spaces also can influence the likelihood for diseases to jump from animals to humans. Experts have linked the recent rapid rise of Avian influenza in Asia to bird habitat loss. Holt said Avian influenza is a worry for people in the United States, but in contrast to Asia, many U.S. national wildlife reserves provide refuges for migratory birds that helps to keep the illness at bay, whereas wetland degradation in other parts of the world may force migrating waterfowl into sites where they have contact with domestic fowl.

Global biodiversity has declined rapidly in the last 60 years and extinction rates are projected to rise dramatically in the next five decades. The patterns described in the paper suggest that there will be correlated, complex effects on disease incidence and emergence, Holt said.

Biodiversity also occurs within individual hosts, such as with humans. Environmental changes, including the overuse of antibiotics, can result in a less bacteria-rich environment within the human body. In the Nature article, the experts suggest that a decline in overall biodiversity will affect the bacterial richness and composition of the human community of microbial symbionts, making the body less able ward off disease.

"When a clinical trial of a drug shows that it works," said Keesing, the paper's lead author, "the trial is halted so the drug can be made available. In a similar way, the protective effect of biodiversity is clear enough that we need to begin implementing policies to preserve it now."

Source: University of Florida