More human-animal interactions means more new outbreaks likely: epidemiologist
TORONTO -- Future outbreaks of infectious diseases, such as the new coronavirus from China, are likely to increase as humans and animals interact in close proximity.
That’s according to Univeristy of Toronto epidemiologist Isha Berry, who specializes in the transmission of infectious diseases between humans and animals. She explains that growing population density and rapid urbanization contribute to a greater overlap between humans and wildlife.
“Humans are encroaching on animal environments,” Berry told CTV’s Your Morning on Tuesday.
Human activity such as deforestation, road building, and mining place people in closer contact with wildlife in remote areas, thus exposing them to unknown viruses they may be carrying, Berry said.
What’s more, the epidemiologist said the increase of wildlife trade and consumption heightens the risk of these viruses entering humans’ food systems.
“There are a lot of different ways or pathways that these different types of pathogens can use to spread,” she said. “For instance, we can think of direct contact, like touching or petting animals or getting bitten by them, or indirect contact, so being in the same place where live animals are roaming around or where they’re living, such as farms or wet markets.”
Animals have already been identified as the primary source for the majority of known infectious diseases, Berry said.
“When we think of newer or emerging infectious diseases, this can actually be 75 per cent, so three in four of these types of diseases are spread from animals,” she explained.
These diseases are known as zoonoses, meaning they are naturally transmissible from vertebrate animals to humans.
Zoonotic viruses in bats
While the exact animal origin of the novel coronavirus from the city of Wuhan, the epicentre of the current outbreak, is still unclear, Chinese scientists have said the virus likely came from bats.
Bats have also been thought to be behind the deadly SARS, or Severe Acute Respiratory Syndrome, that originated in southern China and spread globally in 2002 and 2003. They were also identified as the source of MERS, or Middle East Respiratory Syndrome, that was first reported in 2012.
In those cases, the viruses were believed to be spread by other animals, such as civet cats and camels, before humans contracted them.
A study published in the journal Nature in 2017 found that bats habour a “significantly higher proportion of zoonotic viruses than all other mammalian orders.”
According to the World Health Organization (WHO), the first cases of novel coronavirus occurred in a group of people with pneumonia who had links to a seafood and live animal market in Wuhan where “many fish, reptiles, bats and other live and dead animals were traded.”
The disease then spread from those people to their family members and healthcare workers who were in close contact with them.
“Coronaviruses circulate in a range of animals and can sometimes make the jump from animals to humans, via process known as a “spillover”, which can occur due to a mutation in the virus, or increased contact between animals and humans,” the health organization said.
As of Tuesday, there have been more than 20,000 confirmed cases of the new coronavirus and 425 deaths in mainland China. There have been at least 180 cases, including two fatalities, outside of China.
In terms of finding a solution to the increasing emergence of zoonotic infectious diseases, Berry said prevention is more important than vaccines.
“Vaccines for every new disease are really not sustainable,” she said. “Vaccines take a long time to be developed and deployed so there can be a long lag period.”
Instead, the epidemiologist said prioritizing research and funding to enhance surveillance in areas where there’s human-animal contact would go a long way in preventing these types of diseases from emerging in the first place.
Last week, Chinese authorities temporarily banned the trade of wild animals in response to the new coronavirus outbreak. The ban is expected to continue until the “the epidemic situation is lifted nationwide,” however, some conservationist groups have called for a permanent end to wildlife markets everywhere.
In China, a group of prominent researchers from the Chinese Academy of Sciences, the Wuhan Institute of Virology and the nation’s top universities appealed to the government to crack down on these markets because they increase the probability of an outbreak.
“This is the hidden danger for the trade and consumption of wild animals,” the group’s open letter read.
With files from The Associated Press