The SARS-CoV-2 coronavirus has not been the only deadly virus to emerge throughout recent human history. Multiple other viruses deadly to humans have appeared and disappeared without a trace, as scientists try to decipher the causes that lead to these viruses at the end of their existence.
Severe Acute Respiratory Syndrome (SARS) was first reported in February 2003, the BBC recalled in an article, when the WHO office in Beijing received a tip-off about “a rare contagious disease” that had killed 100 people in just one week.
The Chinese province of Guangdong was the origin of the SARS virus: its local markets, full of exotic species where restaurants lived a few meters away from places where these animals were gutted, were the perfect breeding ground for the spread of this virus.
At that time, health authorities feared that this virus could cause a global pandemic like the one in 1918. However, two years after its detection and after infecting more than 8,000 people worldwide, SARS abruptly disappeared. According to epidemiologist Sarah Cobey of the University of Chicago, sophisticated contact tracing and the peculiarities of the virus – it was easier to identify those infected because there were no asymptomatic people – were key to making it disappear.
In addition to SARS, two other viruses have been able to be extinguished: smallpox and rinderpest. In both cases, vaccines were key to winning the battle against the spread of these viruses. However, Stanley Perlman, a microbiologist at the University of Iowa, says that it is usually “very difficult” for these to go away “when you have a virus that is well adapted.
“SARS is gone because there is no other obvious host,” says Perlman. That virus jumped to humans through a palm civet, a mammal considered a delicacy in China. According to Perlman, the species that transmitted the virus to a human was probably one of the few that became infected directly from a bat.
In the case of influenza, there are two main types: A and B. The first one infects many animals besides humans, while the second type only infects humans. However, there is no trace of the strain that caused the 1918 flu pandemic, nor of the strain that caused the 1957 bird flu outbreak, with 116,000 deaths in the U.S. and almost two millions all around the world.
Epidemiologist Sarah Cobey notes: “If you focus on a particular strain, or rather, any particular genetic sequence that is replicating itself, there is a very, very high extinction rate. According to Cobey, “strains are disappearing every two years. It is complicated, but we are seeing a very high rotation”.
However, some scientists point out that “the term extinct is misleading”. According to Ian Lipkin, an epidemiologist from Columbia University, “viruses can be present in many places; they can lurk in people, they can lurk in materials that are stored in freezers, they can lurk in wildlife and domestic animals; it is really impossible to say if a virus is extinct.
Cobey said, “There are a lot of pathogens out there, most people don’t know how many,” so the Covid-19 pandemic may serve to “reflect on what kind of diseases we want to eradicate.