Human health threatened by loss of species, warn ecologists

Declining biodiversity is increasing the chances of humans being infected by harmful bugs and viruses, say scientists.

Examples include the spread of West Nile virus by mosquitoes, tick-born Lyme disease bacteria, and potentially deadly hantavirus caught from rodents.

All of these infectious agents, or pathogens, become more widespread as a result of reduced biodiversity.

Theoretically, a richer mix of species could either increase or reduce infection rates. Having more varieties of animals, plants and micro-organisms might provide a greater source of organisms and viruses that can infect humans.

But in reality the reverse is true, according to evidence published in the journal Nature. As biodiversity shrinks, the danger from infectious diseases increases.

The species most likely to disappear as biodiversity is lost are often those which provide a "buffer" against disease, the research shows.

Either pathogens cannot live in these species or they end up infecting poor hosts. Surviving species tend to be those that magnify the transmission of infectious diseases.

US ecologist Dr Felicia Keesing, from Bard College in Annandale, New York, who led the research, said: "We knew of specific cases in which declines in biodiversity increase the incidence of disease. But we've learned that the pattern is much more general: biodiversity loss tends to increase pathogen transmission across a wide range of infectious disease systems."

Biodiversity loss in recent years had been accompanied by an increase in contact between humans and animals, for instance through land-clearing and hunting, the researchers pointed out. This provided the "perfect recipe" for infectious disease outbreaks.