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Scientists are trying to find out why some viruses disappear, while others can survive and cause disease for hundreds of years, the BBC reports.
An example is smallpox. When scientists analyzed the DNA of skeletons dating back 1,000 years, they found that the existence of a strain of smallpox, totally different from the one eradicated in the 1970s by vaccination. And that strain of smallpox disappeared hundreds of years ago, with no known cause.
We already know how new viral threats appear: contact with infected animals, the virus that passes from one species to another, the “zero patient” that is infected first, the elements that lead to its spread throughout the world.
But little is known about the end of a virus. Why do some viruses disappear? And what happens to them? As the threat posed by these tiny, primitive life forms grows stronger, scientists struggle to discover more.
SARS, a success story. How it was eradicated
One of the most recent viruses to disappear was SARS. The world became aware of its existence on February 10, 2003, after the World Health Organization office in Beijing received an email describing “a strange contagious disease” that killed 100 people in one week.
The virus infected at least 8,096 people, of whom 774 died. But it could have been a lot worse.
Like its close relative COVID-19, SARS had many of the qualities necessary to spread around the world: It was an RNA virus, meaning it could evolve rapidly and spread via respiratory droplets, which are difficult avoid. At the time, many experts were concerned that the virus could be as devastating as HIV or even the 1918 flu pandemic, which infected a third of the world’s population and killed 50 million people.
Instead, SARS disappeared as suddenly as it appeared. Until January 2004, there were only a few cases until at the end of the month, the last infection was announced. Interestingly, while “patient zero” describes the first known person to be infected with a virus, there is no equivalent label for the last person to become ill. It appears to be a 40-year-old man named Liu from Guangzhou.
How did the virus disappear? According to Sarah Cobey, an epidemiologist at the University of Chicago, SARS was neutralized by combining the detection of all contacts and the peculiarities of the virus itself.
When someone is infected with SARS, the symptoms are very serious. The virus had a staggeringly high mortality rate, nearly one in five patients died, but this meant, on the other hand, that it was relatively easy for infected people to be identified and quarantined. There was no “silent” spread from asymptomatic people, and SARS also had a relatively long incubation period before it became contagious.
Viruses killed by vaccination
Unfortunately, the case of SARS is not common. Only two other viruses could be intentionally eradicated: smallpox and rinderpest, which affects animals.
“It just came to our knowledge then. It’s actually very difficult when you have a well-adapted virus,” says Stanley Perlman, a microbiologist at the University of Iowa.
The war against these viruses has been won with vaccines, which are also on the verge of eliminating polio (cases have been reduced by 99% since the 1980s) and potentially measles, although recently these efforts have been compromised. of the anti-vaccine movement.
On the other hand, other viruses are unlikely to disappear because humans are not their only host.
An example is Ebola. There have been at least 26 outbreaks in Africa since the virus was discovered in 1976, and these are the only ones that have been detected by health authorities. Outbreaks occur when the virus passes from an animal, usually a bat, to a human, who then infects other humans. As long as there are bats, there will be the virus.
And about COVID-19 it is believed that it also started from bats, which reached humans through another animal, possibly the pangolin.
“In the case of COVID-19, the tank is us now,” says Perlman. In fact, it has become such a human virus that scientists have begun to wonder if it will spread and vice versa, that is, if it will pass to humans back into the wild, making it even more difficult to eliminate.
Strains of the influenza virus that self-destruct
There are also viruses that persist and affect people. But while it is possible to stay with our species forever, individual strains of the virus disappear regularly.
An example is the flu. It has two main types: Type A flu, which infects many animals other than humans, is responsible for most cases of seasonal flu and also causes pandemics. Then there is influenza B, which infects only humans and seals, but does not cause pandemics.
For a long time it was thought that the influenza A strains we live with are constantly evolving so that we can become better infected. But the latest scientific research shows that this is not the case.
It seems that no one who died before 1893 was ever infected with any of the influenza A strains that exist today. This is because all flu viruses that have existed in humans until about 120 years ago have disappeared. The strain that caused the 1918 pandemic also disappeared, as well as the one that caused the 1957 bird flu outbreak, which killed up to 116,000 people in the United States, and the type of flu that circulated in 2009, before the flu began swine.
Strains of influenza evolve in various ways, but the vast majority will suddenly disappear. Every few decades, a new type of flu will evolve.
“It’s interesting, because if you focus on a certain strain, or more, any special genetic sequence that replicates, there is a very, very high extinction rate,” says Sarah Cobey. “The stems now go extinct every two years. It’s complicated, but we see a very big change,” he adds.
Interestingly, instead of adapting to humans over time, it appears that H1N1, the type that caused the 1918 flu pandemic and swine flu, and is now gone, had accumulated mutations that were useless or even harmful to its own. survival.
How rapid mutations could be used against the new coronavirus
Now some scientists suggest that accelerating this process would allow us to harness the rapid evolution of endemic human viruses to our advantage. The idea has been around for some time as a way to get rid of the flu and colds, but recently it has been suggested as a way to fight COVID-19.
Speeding up viral development artificially, with drugs that promote mutations at an even higher rate than usual, could have some benefits. First, it could weaken the virus enough to reduce the amount circulating in individual patients. This could make treatment easier for people with serious illnesses. There is already some evidence that this may work: clinical trials in the US and Japan have found the mutation-inducing drug favipiravir to be effective against the H1N1 flu strain. Virologist Elena Govorkova of St Jude Children’s Hospital in Memphis, Tennessee, and her team showed that the drug appears to make the flu virus less infectious.
Second, certain strains of the virus, like the types of COVID-19, there are already at least six, could accumulate enough mutations that are harmful to themselves to disappear completely. In India, there is already evidence that this could happen naturally. The virus is mutating at a staggering rate and it has been suggested that it may be alone.
However, some scientists are skeptical that we can ever say that a virus is gone forever.
“The disappearance deadline can be misleading,” says Ian Lipkin, an epidemiologist at Columbia University in New York.
“Viruses can be present in many places, they can hide in people, in materials stored in freezers, in wild animals and pets, it is really impossible to know if a virus has disappeared,” he says.
Lipkin notes that smallpox bottles still exist in freezers in at least two locations and that there is still a debate about whether or not they should be destroyed.
Editing: Monica Bonea
