A new relationship with animals, nature and each other.

Animal Extinctions Bad for Your Health

Scientists have been discovering that the more animals and plants go extinct, the greater the number of infectious diseases we can all catch.

In a paper published in this week’s issue of the journal Nature, scientists explain how the loss of entire species results in more disease-causing organisms.

“Global change is accelerating, bringing with it a host of unintended consequences,” says Sam Scheiner, of the Ecology of Infectious Diseases (EID) Program.

In fragmented forests, biodiversity declines, leading to infectious diseases like Lyme disease.
Credit: All illustrations by Nicolle Rager-Fuller

As more animals and plants go extinct, the species most likely to disappear are often those that buffer the transmission of infectious diseases like West Nile virus, Lyme disease and hantavirus.

“We knew of specific cases like West Nile virus and hantavirus in which declines in biodiversity increase the incidence of disease,” says Felicia Keesing, an ecologist at Bard College in Annandale, N.Y. “But we’ve learned that the pattern is much more general.”

Global biodiversity has declined at an unprecedented pace since the 1950s. Current extinction rates are estimated at 100 to 1,000 times higher than in past epochs, and are projected to rise dramatically in the next 50 years.

Expanding human populations are already increasing contact with new pathogens as they clear land for agriculture and go hunting.

The scientists point to the growth of Lyme disease, where species like the opossum are lost when forests are fragmented, but white-footed mice thrive and spread the tick-borne disease.

Preserving natural habitats, the authors argue, is the best way to prevent this effect.

Identifying the variables involved in infectious disease emergence is difficult but critical, says co-author Andrew Dobson of Princeton University.

Biodiversity is an important factor, as are land-use change—converting forest to agricultural land—and human population growth and behavior, he says. “When biological diversity declines, and contact with humans increases,” says Andrew Dobson of Princeton University, who is one of the authors of the study, “you have a perfect recipe for infectious disease.”

For humans and other species to remain healthy, it will take more than a village. We need an entire planet, the scientists say, one with its biodiversity thriving.