Health

Why tracing the animal source of coronavirus matters

When viruses sometimes spill over from animals to humans, the health consequences can be serious.

Scientists 'don't want to miss a potential source of an infection,' veterinary professor says

A worker in a protective suit is seen at the closed seafood market in Wuhan, Hubei province, China, on Jan. 10. The seafood market is linked to the outbreak of pneumonia caused by the new strain of coronavirus. (Reuters)

Alongside treating people infected with the new coronavirus, tracing those they've been in contact with and learning how the virus is transmitted, there's another pillar for controlling infectious diseases: searching for its animal host.

Scientists have named the new virus that's caused hundreds of confirmed infections 2019 novel coronavirus (2019-nCoV). The outbreak started in Wuhan, China and travellers have brought the virus to other countries.

So far, the virus seems most closely related to coronaviruses from bats. Many of the patients in Wuhan had a link to a large seafood and live animal market. That origin suggests spread from an animal to a human, according to the U.S. Centers for Disease Control and Prevention's website. 

Viruses in non-human animal hosts tend to invade a certain type of animal cell without harming people. In the case of avian influenza, for example, the virus gets into the intestines and respiratory tracts of birds.

Occasionally, a virus jumps the species barrier to infect human cells.

"We're always on the lookout for the strange ones like SARS," says Dr. Scott Weese, a veterinary professor at the University of Guelph who is interested in novel coronaviruses from the perspective of emerging and infectious diseases.

"We always worry about bats as the original source, but what made it go from a bat to a person? Is there an animal in between and is that something we need to be paying attention to, or is it just human-to-human transmission?"

Find the animal hosts

Animals can be hosts both to viruses that only affect them, and viruses they can spread to humans.

For SARS, civet cats and raccoon dogs were found to carry and spread the virus, as well as domestic cats and ferrets, he said.

A woman wears a mask while pushing a wheelbarrow past the closed Huanan Seafood Wholesale Market on Jan. 17. (Getty Images)

"If we don't know what the host range is, we should assume that it is more than just humans until we prove otherwise because we don't want to miss a potential source of an infection."

Dr. Jeremy Farrar, director of the Wellcome Trust in Britain, where he studies infectious diseases and tropical medicine, noted that this coronavirus has crossed from animals to humans.

"That does not happen often, and it is without doubt very serious," Farrar said in a Science Media Centre commentary.

According to Weese, the majority of emerging diseases have animal origins. The more humans interact with different species and wild environments, the more the risk increases, he said.

Conversely, keeping animal habitats and human habitats apart helps to reduce the risk, Weese said, while acknowledging that isn't completely practical.

Civet cats wait for food in 2004 at a farm in Liuan, China. The country banned selling and eating of civet cats after the animals were confirmed to be host of the SARS coronavirus. (China Photos/Getty Images)

Kerry Bowman, a bioethicist who teaches medical students about environmental change and human health at the University of Toronto, went to the market in Wuhan linked to the first cases of this new coronavirus about 18 months ago. While there, he counted about 50 species including snakes, turtles, wild rabbits, foxes, Asian palm civets and frogs.

'It could easily happen again'

"You've got these extremely stressed animals in really tiny, contained spaces that are clearly unwell," Bowman recalled. "You've got high-powered hoses blasting water constantly and so you've got urine and feces — everything is merging between species sitting in the sun. You can imagine the potential for recombination of viruses."

Bowman said he's loath to criticize another culture's consumption habits. But in his opinion, China's laws of wildlife trade are not well enforced.

China is also not alone. Ebola is spread in different ways and causes different symptoms than respiratory infections, but the Ebola virus is currently spreading person to person in Congo. Just as a coronavirus can originate in animals, people can be exposed to the Ebola virus by eating bushmeat, such as primates.

After SARS killed 44 people in Canada, health officials here and internationally invested in preparing for outbreaks, Bowman said.

"I think we've learned a lot," he said. "But if we don't deal with the heart of the problem where these things can emerge, it could easily happen again."