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A new discovery by scientists suggests that, depending on how much a person becomes infected, they will be asymptomatic, moderately ill or in critical condition.
“Dose
do poison ”is the maxim attributed to Paracelsus, the Swiss physician-philosopher of the early Renaissance. It means that any substance can be toxic if administered in a sufficiently high concentration. Too much water can also remove your electrolytes and become fatal.
Seeing the coronavirus through this prism – that the “dose” of virus you receive will make the difference between being asymptomatic, moderately ill or suffering from a critical condition – can be helpful when thinking about protection against Covid-19 now, when temperatures drop. and the number of cases increases.
SARS-CoV-2 likely behaves like other viruses
The concept that a certain dose of a pathogen – a pathogen – is needed to generate an infection has been demonstrated in many viruses, such as influenza, chickenpox and others, says Erin Bromage, a professor of biology at the university. of Massachusetts. Dartmouth. “If you target an animal with a low enough dose, it will be able to resist without getting sick at all. But at a high dose of pathogens, an infection will occur and the animal will succumb. So the dose becomes really important.”
A certain number of viral particles are not necessary to infect a cell – it only increases the chances of one of those particles entering the cell and infecting it, initiating the chain reaction.
Another approach is like conception: you don’t need millions of sperm to fertilize an egg – just one is enough, but men produce millions to increase the chances of one reaching the egg, puncturing its protection and fertilizing.
A single viral dose or a staggered dose over time
There is another dimension to viral dose and it has to do with time. It is not only the virus dose received at any given time that matters, but also the sum of the viral doses over a period of time. “Some people speculate: Why are bus drivers or emergency personnel, for example, more vulnerable? Because they are exposed to higher doses or because they are in an environment where they are exposed for a long time and receive a wider range ? ”Asks Bromage.
In mid-October, the US Centers for Disease Control and Prevention (CDC) changed the definition of “close contact” to include multiple short exposures totaling 15 minutes or more with an infected person.
It’s not just the virus that matters, it’s the host
“There is a certain dangerous dose of the virus for everyone,” says Bromage. “For someone who is immunocompromised, or someone who is stressed, less exposure to the virus than in a person in good condition can lead to similar results.”
The risk of infection depends on the physiology of the potential host as well as personal health habits and habits such as smoking, diet, physical activity and sleep. The worst case scenario is an elderly and sick person with long and repeated exposures. A medically fragile person may receive a low dose of the virus; on the contrary, a healthy person can be overwhelmed by a high dose.
A tragic example is the death of the young and apparently healthy Dr. Li Wenliang in Wuhan. On December 30, 2019, it sounded the alarm after seeing seven cases of SARS-like disease among hospital patients; four days later he was accused by the police of “serious disruption of the social order” and of “spreading rumors on the net”. Shortly after taking care of his critically ill patients, Li developed symptoms of Covid-19; he died less than a month later. He was only 34 years old.
We are still only talking about possibilities and probabilities. Pointing out the exact scenario leading to infection is much more difficult.
“We can’t study the exact viral dose that can make someone sick because it’s unethical,” says Dr. Monica Gandhi, an infectious disease physician and professor at the University of California, San Francisco (UCSF). It would mean exposing people to progressive doses of the virus to determine when infection occurs.
“I don’t think we’ll actually know a value. We can have animals – there are models of ferrets and hamsters – where the more the more they get sick, it’s useful and can give us information. But unfortunately we won’t know enough about people.”
Viral dose and viral load
“It’s an interesting dance of the two sides of a coin between the dose – what goes in – and the viral load – what comes out,” Gandhi says. Viral load is the amount of virus in the body of an infected person; some studies, not all, have shown that the sicker a patient is with Covid-19, the higher the viral load.
“If you take a lower dose of the virus, you can calmly treat it and isolate it. You have an asymptomatic infection and it is less likely to produce a high viral load, so it is related to a milder disease,” he says. He noted that in places where universal use of a mask has been adopted – such as an Argentine cruise ship and several U.S. food processing plants – the rate of asymptomatic infections, over 80 percent, was more than double. of the general rate of 40% per year. that the CDC has estimated. The mask appears to reduce the dose by filtering out some of the viral particles.
The connection between masks and vaccines
There is, however, another fascinating and important way to think about virus dosage. If the dose is low enough, it may not cause disease, but it may also generate a vaccine-like immune response. It is an extraordinary concept of critical importance.
In fact, Gandhi and co-author Dr. George Rutherford of UCSF’s Department of Epidemiology and Biostatistics published an article in the New England Journal of Medicine in September claiming that wearing a mask, an exposed person would receive a lower dose of the virus than they would. without mask: prevents disease, but activates the immune system response.
In the article, they compared “chickenpox,” as a similar process was called, when people were deliberately exposed to low doses of the virus from a sick person to create immunity. It happened before the vaccine was introduced. “I gave them a little virus and they were a little sick and then they developed an immune response – and it worked perfectly.”
This may also explain why some people never show Covid-19 symptoms but still have antibodies to the virus. But more research will be needed to confirm this.
Because people can’t control whether, much less how much they get from a viral dose, Gandhi reiterated what almost all health experts have said we should do to be as safe as possible: keep physical distance. compared to those outside the home, choose outdoor spaces and not indoor ones, have good hand hygiene and – please – the mask upstairs! (November 2, CNN)
Source: hotnews.ro
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