What Is Spillover Theory? Can It Help Prevent Pandemics?

The crippling effects of pandemics have been felt worldwide since COVID-19 hit in 2020. It took nearly two years for people to embrace the new normal and until today the world is still battling coronavirus. So how do pandemics begin?

What Is Spillover Theory?

According to NPR, the spillover theory refers to animal pathogens that affect people. Initially, researchers thoughts that spillovers were rare events. However, more and more studies show otherwise - they happen all the time.

For instance, COVID-19 began from an animal and it jumped or "spilled over" into people.

Animal viruses tend to remain within their host animal. Scientists have compared the spread of a virus to winning the lottery: The virus is in the right place at the right time, and it also possesses special, rare characteristics that allow it to infect humans. It is extremely rare for all of these events to occur simultaneously. That was what they thought.

This theory has influenced the way in which scientists search for new pathogens or attempt to predict which ones will cause future pandemics. In particular, it led scientists to concentrate their efforts on discovering new viruses in wild animals. Since 2009, the U.S. government has spent hundreds of millions of dollars trapping wild animals such as bats and rodents, cataloging all the viruses circulating in their bodies, and then attempting to predict which of these viruses will most likely cause a costly outbreak or pandemic among humans. Unfortunately, this effort failed to detect SARS-CoV-2 prior to the virus's global spread.

In recent years, an increasing number of virologists and epidemiologists have questioned the viability of this strategy. Some have openly stated that it will not work.

However, the report noted a 5-month-old infant in 2017 who got ill and had pneumonia. They later realized that the baby had contracted the virus from a dog. Virologist Anastasia Vlasova, a world expert on coronaviruses said that initially, many thought dog and cat viruses would not infect people. However, when she tested the virus from the baby, it grew very well in a broth containing dog cells, suggesting that the dog virus infected the baby's respiratory tract.

Surprisingly, when Vlasova sequenced the virus' genes, she learned that it could have come from pigs or cats as well.

It remains unknown how the infant was infected by the virus. The baby could be the first known case of the seventh coronavirus known to infect people, but he wasn't the only one - not in the least.

Is Spillover Feasible?

Like virus cataloging projects, virus discovery [in wild animals] is scientifically interesting, according to evolutionary biologist Stephen Goldstein from the University of Utah.

From the perspective of predicting pandemics, however, he believes it is a ridiculous concept. For him, the numbers just don't make sense and only a small fraction of the viruses found in animals will ever be able to infect humans.

However, he also added that he doesn't think spillovers are extremely rare because when people start looking for them, they find them. Spillovers aren't necessarily needles in a haystack but more like a rake sticking out of the side of the haystack.

Dr. Gregory Gray, an infectious disease epidemiologist at the University of Texas Medical Branch in Galveston, added that scientists lack the resources and funding to detect new viruses within humans.

Gray believes that there are likely novel viruses infecting people who work extensively with animals, particularly domestic animals, in North America and they probably miss them because they lack the equipment to collect them.

Marco Salemi at the University of Florida said people breathe thousands of different bacterial and virus strains. We catch viruses by touching surfaces, breathing and even petting our pets. He noted that animal viruses are everywhere.

Salemi shared two points about spillovers. First, the majority of spillovers don't harm people because our immune systems fight the pathogen without having symptoms at all. When a virus triggers symptoms, it masquerades as cold, flu or stomach bug.

Additionally, the virus only infects a few people because the pathogen cannot infect a large number of people as they aren't adapted to live in humans.

Second, he realized frequent spillovers could help researchers stop the next pandemic.

Check out more news and information on COVID-19 in Science Times.