An example of how Worobey and his team modeled of COVID’s mutation and spread.

The University of Arizona is hosting a free, online lecture series to help the public better understand specific aspects of COVID-19, including how the virus spread throughout the world, and our eventual return to normalcy. The monthly series includes five talks, each hosted by a different UA faculty member, ranging from statisticians to professors of medicine. 

The first talk in the series took place Monday, Feb. 15, when Michael Worobey, a professor of ecology and evolutionary biology, discussed the origins of the pandemic and how the virus made its way into the United States. Worobey uses an evolutionary approach to understand the origins, emergence and control of pathogens. For decades, he has studied outbreaks such as the 1918 Spanish influenza pandemic and HIV.

Worobey’s presentation began with a discussion on the virus’ animal origins: A bat virus ultimately got into humans, but scientists don’t know if the transmission was directly from bats to humans, or if another species (possibly pangolins or cats) was caught in between. 

Horseshoe bats harbor multiple viruses similar to SARS-CoV-2, the novel coronavirus that causes coronavirus disease 2019 (COVID-19). In fact, after the 2002–2004 SARS outbreak, scientists studying these bats found that 20% to 30% had been exposed to the previous SARS virus.

“In a way, it’s not a surprise this virus jumped,” Worobey said. “We knew it had the capacity to do it, and sure enough it did it again.”

Worobey says scientists are sure the current coronavirus came from bats due to its similarity to other bat viruses. In fact, COVID’s genetic material is 96% identical to RaTG13, a bat virus sampled prior to the current pandemic. 

Worobey and his team studied the infection of a patient titled WA1 (Washington 1), the first known case of COVID-19 in the United States. While Washington state was an early hotspot for COVID in the Americas, tracking the genetic mutation of the virus throughout multiple Americans shows that first patient may not be to blame for the broader outbreak. 

“We decided to rerun the epidemic in our computers over and over again under the assumption that the outbreak in Washington state did start with WA1,” Worobey said.  “With this highly replicated simulation, we can rerun the tape of the outbreak and the evolution of the virus over and over again, and they tell us it’s very, very unlikely WA1 actually started this outbreak.” 

The simulations say this is the case because, had the Washington outbreak entirely stemmed from WA1, the virus’ mutations in multiple patients would not be as diverse as are found, some of which have lineages that can be traced back to other provinces in China, showing multiple transmission between countries. 

“So we probably were successful in using tools like contract tracing and case isolation to limit and block onward spread of WA1’s virus,” Worobey said. “There’s a lot of scapegoating and blaming of people from China for the outbreak itself... and the fact our study refuted the notion that this guy was the ‘patient zero ‘ of the North American outbreak is really important.”

Worobey also says there’s a misunderstanding about the Trump Administration’s travel ban on China enacted in the early days of February 2020; although Chinese nationals were barred from travel, roughly 40,000 American citizens and visa holders were still permitted to travel between the countries, which may have resulted in multiple international transmissions.

“If that is what happened, some of the blame for the establishment of this outbreak needs to go to the authorities who were screening those 40,000 people, because that screening was notoriously lax,” Worobey said. “You could hop off a plane and move out into the community with really just one question like ‘Do you have a fever?’, which is not a good way of screening for this virus.”

While evidence shows the earliest COVID cases in the United States came directly from China, even more cases can be sourced back to Europe, which then can be sourced to China. 

“Here in Arizona, almost all of the genomes that are circulating trace back to this Hubei-to-Italy-to-North America jump of the virus,” Worobey said. “But one interesting thing that came out of this study is that if you re-ran the simulations again and dropped SARS-CoV-2 into the human population in one person, 70% of the time, it would go extinct by itself. Unfortunately, we’re living in a world where that unlucky 30% prevailed.”

The next talk in the series will feature Bonnie LaFleur, a research professor of biostatistics, discussing our transition back to normalcy on March 15 from 5 to 6 p.m. The following talks are by Floyd Chilton, a professor of nutritional sciences, discussing why COVID-19 is so severe for certain patients on April 19; Yves Lussier, a professor of medicine, discussing the significance of single-subject studies in post-genomic analyses on May 17; and John Ruiz, an associate clinical professor, discussing COVID-19 “Risk, Resilience, and Recovery” on June 21.


Anyone interested in attending the virtual series can register for each event at 

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