Declines in wildlife drive rodent-borne diseases
It’s bad enough that the world is losing elephants, rhinos, and other large mammals so quickly. But their disappearance can have ecosystem-wide implications. When large wildlife species decline, rodent populations rise rapidly — and so does the prevalence of the diseases they carry.
For example, Bartonella bacteria cause an infection in rodents and their fleas. The jumpy parasites are vectors for spreading the disease to humans, where bartonellosis can lead to joint swelling and memory loss. This and other zoonotic diseases — those transmitted between animals and humans — tend to become more common with wildlife loss, but no one knows exactly what’s behind the trend.
To study how large mammal declines affect the prevalence of disease, a team led by Stanford University’s Rodolfo Dirzo used the Kenya Long-Term Exclosure Experiment as a testing ground. The enclosure comprises several hectares of savannah ecosystem in central Kenya that have been fenced off since 1995 to keep out animals larger than 15 kilograms. The team spent three years measuring Bartonella inside and outside the area, capturing (and releasing) a total of 832 rodents from 11 species of mice, rats, and gerbils. They collected blood samples from the rodents, as well the 1,570 fleas the rodents hosted.
In the areas that excluded large wildlife, rodent and flea populations doubled compared with areas outside the fences. The loss of predators is a common explanation when a population explodes. But in this case, without large herbivores controlling rodent density — through changes in the area’s vegetation, as well as direct competition for food resources — the population of infected rodents grew twofold.
With the health of the ecosystem, wildlife, and humans interlinked, defaunation of larger species ultimately increases the risk for people contracting disease. And that offers another compelling reason to conserve biodiversity. — Janet Fang | 1 May 2014
Source: Young, H.S. et al. Declines in large wildlife increase landscape-level prevalence of rodent-borne disease in Africa, Proceedings of the National Academy of Sciences (2014). doi/10.1073/pnas.1404958111
Images: Hillary Young (gerbil) & Michael Hastriter (flea) via Smithsonian
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