Day 6

How climate change could make outbreaks like COVID-19 more common

Infectious disease specialist Christine Johnson says habitat destruction means humans will live in closer proximity to wildlife, while rising temperatures increase the range of mosquitoes, ticks and other insects known to transmit diseases.

'Tackling climate change is a public health imperative,' says infectious disease expert Christine Johnson

Christine Johnson, an infectious disease specialist, says a virus can cause an outbreak once it begins to transmit person to person. As the climate changes, she believes this could become more common. (Aaron Favila/Associated Press)

Infectious outbreaks, like the novel coronavirus, could become more common as climate change forces animals and humans to live in closer proximity, according to an infectious disease specialist. 

Diseases already spread from wildlife to humans, says Christine Johnson, director at the One Health Institute at UC Davis in California, adding that about 75 per cent of viruses that infect humans originate from animals and insects.

But, she believes that as climate change progresses, outbreaks like the novel coronavirus will become more frequent. 

That virus, which causes an illness now known as COVID-19, has been linked to bats in China's Hubei province and was reportedly transmitted to humans in a market in Wuhan in December 2019. 

Cases of COVID-19 have been reported across the world, infecting over 48,000 and killing 1,381 people, according to the World Health Organization as of Friday. 

Johnson believes that mitigating climate change is a 'public health imperative.' (The Associated Press/Rich Bowmer)

As populations grow and urban sprawl destroys habitats, wild animals are being forced to move in closer proximity to humans, says Johnson. Increased contact between animals and humans allows disease transmission to become more prevalent. 

"We see how rodents that might have been living in more pristine areas move into crops. They are now exposed to people working in agriculture, or [they] move into people's homes … for shelter," Johnson told Day 6 host Brent Bambury. 

"When it comes to emerging infectious diseases, we worry about things that we can get directly through contact with wildlife."

Viruses can be transmitted through animal or insect bites, as well as airborne pathogens. 

As temperatures rise, mosquitoes, ticks and other insects carrying diseases, like malaria, can travel further to areas they wouldn't otherwise be able to survive due to cold weather. 

"As climate conditions change through increased warming periods, [or] changes in rainfall, we've already started to see changes in distributions of mosquitoes, some of which are known to be vectors for pathogens that affect humans," said Johnson. 

COVID-19 is not the first illness to transmit from animals to humans in the last 20 years. The SARS outbreak in 2002 was reportedly transmitted from bats to other animals, including cats, before infecting humans in the Guangdong province of southern China.

Christine Johnson spent a decade studying emerging infectious diseases. She found that mammals, such as bats, have "hundreds and hundreds" of coronaviruses. Bats have reportedly transmitted both the SARS illness and COVID-19 to humans. (Peter Thomson/Associated Press)

Climate change is a public health issue 

Over the past decade, Johnson studied emerging infectious diseases as the director of PREDICT, a project funded by the United States Agency for Public Development. 

"We discovered well over 1,000 viruses that had not been known to man," said Johnson. "It was a big effort to focus on viruses that we think could be a potential pandemic."

About 100 of the emerging diseases discovered in the PREDICT program were in the coronavirus family and travelling among mammals, including bats. 

"There's hundreds and hundreds of coronaviruses in mammal species and bird species," said Johnson. "Species have always had these viruses and they haven't jumped over [to humans]." 

Coronavirus strains living in wildlife only become an outbreak when transmitted from human to human, as seen in the novel coronavirus outbreak. Johnson believes mitigating climate change is crucial to prevent disease transmission. 

"Tackling climate change is a public health imperative," said Johnson. "I think people are becoming increasingly aware of our dependence on the environment."

Written and produced by Martha Currie.

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