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What does it mean when a virus mutates? It’s a previously arcane and scientific question that has become particularly pertinent as the threat of a new Sars-Cov-2 variant has wreaked havoc in Britain and beyond.
B.1.1.7 – also known as VUI-202012/01 (the first “variant under investigation” in December) – is far from the first change detected in the coronavirus. More than 12,000 mutations were detected in the first 50,000 Sars-Cov-2 genomes studied and scientists have now recorded more than four times that number.
Most of these mutations have little impact. They are similar to misspelling a word, the letters are mixed up but the meaning remains the same. But occasionally, a mutation will trigger a behavior change in a virus.
This is the case of B.1.1.7. Nervtag, a subcommittee of the UK’s Sage scientific advisory group, has said it is “very confident” that the new variant appears to increase the virus’s ability to infect cells. They are also concerned that it is quickly replacing other versions of the virus.
But for some, the increased transmissibility could contradictory disguise some positives.
“The general rule of thumb in virology is that better transmission is associated with milder disease,” says Ian Jones, professor of virology at the University of Reading.
“So even if the transmission is higher, the virus may be less dangerous.”
If a virus mutates to become more lethal, it is likely to kill the people it infects before it has a chance to pass to other people and spread widely. Take Ebola – Infected patients develop symptoms quickly and have a very high death rate, reducing the chance of spread.
Professor Jones points to laboratory analysis of avian flu as a good example. “[Experiments] are known to show that H5 [avian influenza virus] it could become transmissible, but when that happened, the virus did not kill any of the animals used, “he says. In short, the virus was either deadly or highly infectious.
The 1918 Spanish flu pandemic seems to prove this point. It is thought, but not proven, that the second wave was more deadly due to a change in the H1N1 virus. By 1920, the virus had evolved to become less lethal; now it causes seasonal flu.
However, other scientists are skeptical.
“It’s not always true,” says Jonathan Ball, professor of virology at the University of Nottingham. “Evolution can favor a virus that can persist and transmit more.” Rabies, for example, is spread by the aggressive disease it triggers.
So what does this all mean for Sars-Cov-2? Experts remain divided on whether the virus is likely to mutate to become more, or less, deadly. But they all insist that we must not give the virus the space to find out.
“Whenever you allow something to be transmitted in humans, you are giving the virus a chance to evolve and find a set of mutations that are advantageous,” says Professor Ball. “That is unavoidable”.
Irish independent
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