Nature

New Maps Show Where Rats, Bats, and Monkeys May Transmit Diseases to Humans

June 14, 2016 | Erica Tennenhouse

Map of zoonotic diseases
Photo credit: DREW KRAMER. Map showing overlapping geographic ranges of zoonotic diseases carried by wild land mammal hosts from 27 orders. Image has been cropped.

Unexpected global trends in animal-borne diseases are revealed.

Animal-borne (zoonotic) pathogens are responsible for a growing number of emerging infectious diseases worldwide. Though the majority of these diseases originated in mammals, little is known about current distributions of mammalian hosts and the pathogens they carry.

Researchers have now assembled world maps revealing geographical ranges of zoonotic diseases carried by land mammals. Published in the journal Trends in Parasitology, the maps feature over 5,000 mammal species from 27 groups, including rabid bats, camels carrying Middle East respiratory syndrome, and the relatives of livestock that pass on food-borne diseases.

Though outbreaks of diseases caused by zoonoses are thought to be unpredictable, the maps reveal some previously unknown patterns.

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"I was rather surprised to see that hotspots of zoonotic diseases didn't match hotspots of biodiversity more closely," said first author Barbara Han, a disease ecologist at the Cary Institute of Ecosystem Studies in New York, in a press release.

"For example, there is high species diversity in the tropics, so I expected to see a similar pattern of more zoonotic parasites and pathogens in the tropics as well. We do find more zoonotic hosts in the tropics, but we find more zoonotic diseases in temperate regions, possibly because these diseases can occur in multiple host species."

Another finding was that more than 10 percent of rodent species (244 of 2,220) are zoonotic hosts. And while there are fewer primate species, a greater proportion of primates (21 percent; 77 of 356) are zoonotic hosts.

Bats, on the other hand, carry far fewer zoonotic diseases than rodents, primates, carnivores, or hooved mammals, despite their bad reputation as disease reservoirs.

Rodent hosts were found to be most prominent in Europe and Russia, while bat hosts appear to be concentrated in Central America, and the majority of primate hosts reside in equatorial Africa.

“We also see that even though there are more species in the tropics, fewer of them carry zoonoses," said Han. "In contrast, more of the species living in northern latitudes, such as the Arctic Circle, carry more zoonoses. Understanding the implications of this pattern in light of climate warming trends will be an important line of inquiry that should be addressed sooner rather than later."

The map data were obtained from information in the Global Infectious Disease and Epidemiology Network (GIDEON) database and from mammal distribution maps published by the International Union for the Conservation of Nature.

"Understanding where animals are distributed and why may not seem applicable to our day-to-day lives," said Han. "But the big breakthroughs that we need as a society (e.g., forecasting where the next zoonotic disease may emerge) rely on exactly this kind of basic scientific knowledge."

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