Species decline compounds health risks

CORNELL (US) — The decline of species due to habitat loss, pollution, and climate change increases the risk of infectious diseases for humans, animals, and plants.

The species most likely to disappear are those that buffer against infectious disease transmission, while surviving species tend to be the ones that increase disease transmission, such as West Nile virus, Lyme disease, and Hantavirus.

A new study published in the journal Nature that examines the link between the loss of biodiversity and infectious disease, also finds patterns among various types of pathogens—viruses, bacteria, and fungi—and hosts.

Since the 1950s, species extinction rates have skyrocketed up to 1,000 times more than in past epochs and are only expected to rise in the next 50 years.

“Normal functioning biodiversity pays off in health benefits for people,” says Drew Harvell, professor of ecology and evolutionary biology at Cornell University.

For example, when forests are fragmented, opossum numbers decline and white-footed mice thrive. Opossums serve as buffers for Lyme disease because they absorb and kill some of the ticks that carry the disease; at the same time, mice amplify both the numbers of ticks and the Lyme disease pathogen.

Scientists don’t know why the most resilient species, such as mice, are the ones that also amplify pathogens.

Protecting natural habitats would be the best strategy to prevent this effect, according to the paper.

Also, as human populations grow, so does contact with pathogens through such activities as hunting and clearing land for farming. The research recommends that officials should carefully monitor animal and fish farms where diseases might jump from livestock to humans or wildlife.

For the study, Harvell examined the pattern in marine ecosystems. For example, climate change is warming the oceans and stressing tropical species like coral, triggering a sudden shift from diverse, beneficial bacteria on the coral surface to less diverse, pathogenic bacteria that lead to coral disease.

“We are dealing with a new equation relating to disease spread, climate change, and biodiversity,” she says. “In the oceans, disease outbreaks are being accelerated by climate warming before we even know the links in the biodiversity chain.”

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