As the number of confirmed COVID-19 cases around the world approaches 15 million, scientists have yet to identify the origin of SARS-COV-2, the virus that caused the disease.
As officials raced to identify the cause of the virus, some turned their attention to wet markets after it was discovered that 27 of the initial 41 patients hospitalized for the virus visited the Huanan Seafood Wholesale Market in Wuhan, China.
Calls to close wet markets followed the outbreak of the pandemic, but these markets account for a large portion of many consumers’ food supply and are of great importance, according to the U.N. Food and Agriculture Organization (FAO).
And some scientists believe that they may never know how COVID-19 infected the first person, making the journey to find the origins of the virus more complicated.
To date, scientists from the Centers for Disease Control and Prevention (CDC) confirmed that SARS-COV-2 is a type of coronavirus. It belongs to the same group of viruses that caused Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS), which left thousands infected and hundreds dead. All three of these diseases are zoonotic, meaning they can spread between animals and humans.
“The reason we now have a pandemic is because that virus has the ability to not only move from an animal to a person but to very effectively be transmitted onwards from one person to another,” Dr. Christopher Olsen, the Director of the Graduate Global Health Program at The University of Wisconsin, tells Food Tank.
Recently, researchers have considered a species of bat, known to carry coronaviruses, to be a vector of the virus. Dr. Christine Petersen, Director of the Center for Emerging Infectious Diseases at the University of Iowa, tells Food Tank that the sequencing from the proteins of SARS-COV-2 aligns most closely with viruses that scientists have found in horseshoe bats. This means the virus that causes COVID-19 seems to be genetically related to a virus carried by the bats. Petersen says scientists think this bat species “is the reservoir for the original SARS virus and MERS virus.”
But a recent study from the Chinese Academy of Sciences in Wuhan, China found that the coronavirus in bats and in humans differ in key ways, suggesting that another mammal may be responsible for transmitting the virus to humans. At a press conference in February, researchers at South China Agricultural University (SCAU) in Guangzhou, China proposed that the pangolin might be this intermediary host.
Although the selling, trading, or poaching of pangolins is illegal, it remains the most trafficked animal in the world. Many people seek the animal for its scales, which are used for medicinal purposes. Others hunt pangolins as bushmeat, which often refers to the meat of wild animals in the forests and savannas in Africa that people consume.
The consumption of bushmeat, which was implicated in the 2014 Ebola outbreak in West Africa, can hold a negative connotation. But this food source often serves as a “cheap and accessible protein source [that’s] really critical for the people…in Africa,” says Petersen. “It has both a positive and a negative impact and that’s something we need to remember.”
But definitive evidence around the pangolin’s role in transmitting SARS-COV-2 remains elusive. In the study from SCAU, researchers found that the DNA of the virus in pangolins was a 90.3 percent match to that in humans. And a specific site, known as the receptor-binding domain (RBD), of the virus in pangolins was a 99 percent match to the RBD of the virus in humans.
The RBD is the component of the virus that helps it invade a host’s cells, causing infection. But, while this site is important for transmission of the virus, even a 99 percent match is not enough to conclude that pangolins spread the virus to humans says a virologist at Duke-National University of Singapore Medical School.
“The pangolin is a more complicated story,” Petersen tells Food Tank. She says that the epidemiological evidence is based on genetic sequencing, and isn’t strong enough to prove that human consumption of pangolins caused the infection. “The actual consensus belief is that although the pangolin has a similar coronavirus it probably is not as related to the outbreak.”
On April 29, a team of researchers from Duke University reported that an unidentified third species could have incubated the virus before it was spread to humans.
“There are still potentially other animals, like pangolins, that appear in live animal markets that still need to be considered. But for now, that is the best information we have,” Olsen tells Food Tank.
Although the evidence for pangolins remains inconclusive, scientists hope that future research in China can uncover the origins of the virus. Currently researchers from Columbia University, Sun Yat-sen University in Guangzhou, China, and other research institutions in the United States and China are working together to learn more about SARS-COV-2 and similar viruses. By finding the source of the virus, scientists could assist public officials in containing the current outbreak and possibly prevent future pandemics.
Photo courtesy of the National Cancer Institute, Unsplash