Animals we domesticated long ago pose disease risk

1 July 2014 by Tamera Jones

Animals we domesticated long ago, such as cats, dogs, pigs and cows, are those that have given us the most parasites, pathogens and other nasties, according to the latest study.

Arabian camel

Arabian camel

The researchers found that such animals are an important source of new diseases, including swine flu which comes from pigs, BSE from cattle and salmonella from chickens.

"Domestic animals act like reservoirs for a range of diseases, many of which originally came from wild animals," says epidemiologist Professor Matthew Baylis of the University of Liverpool, co-author of the study, published in Infection, Genetics and Evolution.

"And it seems the longer ago these animals were domesticated, the more likely we are to share diseases with them."

The speed at which emerging infectious diseases have arisen has increased dramatically over the last 100 years.

Scientists know that around 60 per cent of human pathogens have an animal origin. But, until now, they knew very little about which sorts of animals many of these diseases came from.

Domestic animals act like reservoirs for a range of diseases, many of which originally came from wild animals.

- Professor Matthew Baylis of the University of Liverpool

Studies have pointed to wildlife as the likely source of new diseases. But scientists suspect that domestic animals - which act like reservoirs and amplify diseases emerging from the wild - could be contributing to the speed at which these diseases are emerging.

In an attempt to confirm this, Baylis and his colleagues created network maps using three different sources of data to record common interactions between people and animals and estimate which host animals could be sources of disease.

"We wanted to build up an understanding of what pathogens we have already and where they come from to understand how emerging infectious diseases arise," he says.

"HIV came from chimps, SARS from bats. So what are the characteristics of those host animals?" he adds.

Baylis and his colleagues found that the longer ago an animal had been domesticated, the more likely we are to share pathogens with that animal.

"We found we share many diseases with most domestic animals, with the largest numbers from dogs, cows, pigs, sheep and goats," he says.

Dogs, sheep, goats and pigs were among the first animals to be domesticated. People started living or working with dogs as far back as 17,000 years ago, and they began farming sheep around 12,000 years ago. This means they could have and could still quite easily pass any new pathogens they encounter in the wild on to us.

But it seems animals we domesticated long ago aren't the only source of emerging infectious disease: newly domesticated animals could also be a source of new diseases.

The deadly MERS virus only appeared in Saudi Arabia about two years ago, and has so far killed over 250 people. At the moment, there is no known cure for the virus, which causes severe respiratory illness. Scientists think it came directly from camels, which we only started working with about 5,000 years ago.

"Our research suggests that as well as pigs, goats, dogs and such like, we also need to be concerned about newly domesticated animals we've only fairly recently started working with, like camels, llamas and alpacas, because we haven't been around them long enough to share all of their diseases," says Baylis.

One of the databases used in the study - EID2 - was created with funds from NERC and the Biotechnology & Biological Sciences Research Council, among others.

Serge Morand, K Marie McIntyre, Matthew Baylis, 'Domesticated animals and human infectious diseases of zoonotic origins: Domestication time matters', Infection, Genetics and Evolution, Volume 24, June 2014, Pages 76-81, published online 15 March 2014.