Campus Queries is a series in which Daily Bruin readers and staff present scientific questions that UCLA professors and experts must answer.
Q: Is there a link between environmental issues and the COVID-19 pandemic?
A: Habitat destruction, wildlife markets and climate change may be linked to zoonotic fallout like the one that caused the COVID-19 pandemic, while the link between biodiversity loss and the pandemic is less clear .
SARS-CoV-2, which causes COVID-19, is a zoonotic virus that likely originated in horseshoe bats in China, said Amandine Gamble, postdoctoral researcher at UCLA’s Lloyd-Smith Laboratory.
Zoonotic viruses spread from exclusive animal hosts to humans during a zoonotic spillover event, said Thomas Smith, professor of ecology and evolutionary biology at UCLA.
Zoonotic disease outbreaks are the result of increased contact between humans and wild animals due to processes such as deforestation and habitat destruction, Gamble said. For example, if forest fruit trees disappear due to deforestation, bats are more likely to go into people’s gardens to feed on cultivated fruit trees, creating opportunities for more zoonotic spillover between wild animals and humans, she said.
A 2007 study by researchers at the University of Hong Kong warned that horseshoe bats naturally harbor viruses similar to SARS-CoV and that the practice of eating wild animals in southern China was a “ticking time bomb” for the re-emergence of another SARS-like virus.
This study was published after the 2003 SARS outbreak in Hong Kong. Thirteen years later, the COVID-19 epidemic occurred.
It’s unclear how SARS-CoV-2 began infecting humans, but researchers believe an intermediate host allowed transmission from bats to humans, Gamble said.
A popular theory for the SARS-CoV-2 intermediary is pangolins, which are common in Chinese wildlife markets, but there is little evidence to support this theory, Gamble said. The virus detected on the pangolin was closely related, but not the same as the one responsible for the pandemic, she said.
These types of spillover events are not exclusive to coronaviruses. Henipaviruses, another type of virus found in fruit bats, are transmitted directly from bats to humans in Bangladesh through the palm sap they drink, Gamble said. In Malaysia, henipaviruses are transmitted from bats to pigs on pig farms while bats eat fruit there and people get infected from pigs, she added.
Wildlife markets are also a hotbed for transmission, as wild animals around the world are kept in small cages close to each other, Smith said. Animals defecate on top of each other and are often slaughtered next to each other, creating optimal conditions for virus transfer from animal to animal, he said.
The link between biodiversity loss and zoonotic fallout is less clear. Biodiversity loss can be broadly defined as the decrease in the number and variety of species. Earth is currently experiencing its sixth mass extinction, caused by human factors, according to a study supported by the National Autonomous University of Mexico and Stanford University.
It remains unclear whether the extinction event and zoonotic fallout are correlated.
“We don’t know if having more species actually creates a better environment for the virus to reproduce and evolve. … So you might think that having more biodiversity will lead to more zoonotic spillover events,” Gamble said. “But there’s also what we call a ‘dilution effect’ – the more species you have available to parasites, the less likely they are to end up in humans.”
However, zoonotic fallout is ultimately difficult to detect, making it difficult to quantify the correlation between biodiversity and fallout, she added.
When talking about biodiversity loss and habitat destruction, it doesn’t take long for climate change to enter the conversation, Smith said. As the planet warms, humans and animals are moving to cooler places, he said.
“That means there will be a lot more mixing – animals are going places they haven’t been before, and so are humans,” Smith said. “From a pandemic point of view, I think it is possible to see a lot more fallout from these types of diseases. It’s sort of the link between climate change and pandemics.
There have been reports of improved air quality due to reduced human activity during the pandemic. However, when carbon emissions fell sharply after past recessions, they rebounded and negated any short-term decrease in emissions, according to a BBC Future article. To achieve a long-term effect, there must be big changes, such as a move towards clean energy, according to Glen Peters of the Center for International Climate and Environmental Research in Oslo.
“I think as soon as a vaccine is found, people will go back to driving their cars and doing as much as they used to,” Smith said. “The hope is that this pandemic will be a wake-up call for people to think about how they are changing the climate and the biodiversity we all depend on.”