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Covid-19: Why does hand sanitizer and hand-washing work?
“The common hand sanitizers work only on certain types of virus, including coronaviruses,” explains Mette Myrmel, a virologist at the Institute of Marine Research.
“The Covid-19 virus has a fatty coating, a so-called lipid envelope, a membrane which it ‘puts on’ when it leaves our cells. Alcohol based hand sanitizer dissolves this envelope, destroying the virus,” says Myrmel.
Common diarrhea virus survives longer outside our bodies
Viruses with this kind of fatty coating remain active in the environment, in other words outside a host, for less time than other types of virus such as the norovirus, a common cause of food poisoning or diarrhea.
“Hand sanitizer doesn’t work against noroviruses. They can remain active on surfaces for several weeks, particularly if it is cold and there is little sunlight (UV radiation). This makes noroviruses exceptionally contagious,” says Myrmel.
Hand-washing physically removes nasties
This leaves hand-washing as the only solution. But how does hand-washing really work? Microbiologist Bjørn Tore Lunestad explains:
“It works because the soap binds to fat and dirt on our skin, dissolving it. When you rinse it off, the viruses and bacteria go too. They are mechanically removed from your hands. For coronaviruses, the soap also destroys that fatty coating,” explains Lunestad.
“Is having naturally dry hands an advantage?”
“If thousands of people have touched a surface, they will have left behind fat on it, and potentially virus particles, which you get on your hands if you touch the surface. I don’t think it makes any difference how much fat there is on your hands previously.”
“Warm water also dissolves fat and makes the soap more effective. The water temperature isn’t high enough to kill bacteria and viruses by itself.”
You cannot "kill" viruses
“Actually, I prefer to say that viruses are destroyed or inactivated – not killed. After all, they aren’t living beings,” adds Lunestad.
At the very least, it’s arguable, from a linguistic and philosophical point of view.
“Viruses don’t have any will; they are advanced chemistry. Some people call them rogue genetic material. They are dependent on the cells of other organisms to reproduce, or rather replicate themselves,” he explains.
Viruses destroy our cells
Viruses generally prefer one type of cell in one type of host. When the virus comes into contact with the 'right' type of cell and is taken up by it, the virus takes over the cell and instructs it to make new virus particles. In this process, the cell is destroyed. We develop symptoms if enough cells are destroyed.
"So do as the health authorities says: Wash your hands thoroughly and for plenty of time, or use hand sanitizer when that’s not an option,” is the scientists' advice.
Is there Covid-19 in the sea?
- Noroviruses are carried into the sea with sewage, and they are known to accumulate in bivalves, which we can then get sick from eating uncooked.
- Because coronaviruses need their fatty coating in order to infect new hosts, they don’t survive for very long in the environment.
- The risk of Covid-19 spreading through faeces and sewage also appears to be very low.
- “Even if bivalves, in theory, could accumulate new coronavirus from seawater, it would probably be destroyed by their digestive system,” says virologist Mette Myrmel.
- Early reports suggested that Covid-19 had crossed to humans at a fish market in China. It is unlikely that fish played a role – most probably the virus came from a mammal. A person breathed in the air that the animal had breathed out.
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