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Coronavirus: Should We Be Wiping Doorhandles With Warm Yoghurt?
First published: 28th February 2020
It sounds like a radical, or even crazy, idea for controlling #COVID-19 spread, but maybe it should be evaluated scientifically.
Spread and Disinfection
Coronavirus disease 2019 (COVID-19) is primarily spread between people by small droplets from infected individuals when they breathe or cough. Hand washing, maintaining distance from people who are coughing, and not touching one's face are recommended to prevent the disease. The droplets can land on surfaces and the virus may remain active for hours or days, so that other people touching the surface may pick up the virus, transfer it to their mouth or nose, and thus infect themselves.
As a response, most lift buttons in Hong Kong are now covered with plastic, and signs tell us they are disinfected frequently, perhaps hourly. Elsewhere in China, entire cities are being spayed with disinfectant.
Advantages and Disadvantages of Disinfection
Our response to COVID-19 is based on what scientists found out during and after the SARS outbreak in 2002 and MERS outbreak in 2012, these are all caused by coronaviruses, so there is good reason to think that the particular virus causing COVID-19 will behave in a similar way. Severalstudies have shown that coronaviruses can persist on surfaces for 5 days, or even as long as 28 days. Another study showed that coronaviruses are readily inactivated by disinfectants, including ethanol, isopropanol, benzalkonium chloride, iodophor, sodium hypochlorite, sodium chlorite, cresol soap and formaldehyde.
However, disinfectant is expensive, especially if you try to spray an entire city, daily. Then there is the issue of concentration and toxicity. All disinfectants are somewhat toxic, after all, they are used to kill living things, just not significantly toxic to humans when used in controlled conditions. Even ethanol (alcohol) can cause skin irritation (along with the well-known effects of drunkenness, coma and death when ingested in increasing quantities, but you're not supposed to be drinking the disinfectant supplies); formaldehyde is known to cause cancer; and sodium hypochlorite can react to release poisonous chlorine gas. One problem with mass use of disinfectants is that sufficient needs to be used to make sure everywhere gets a high-enough dose to be effective, with the inevitable result that some areas get excessive coverage.
Disinfectants also only act for a limited time. They are applied, kill whatever is there at the time, and then quickly stop working. Alcohol evaporates, sodium hypochlorite reacts to form less-effective compounds, and anything gets diluted. If new contamination occurs afterwards, it stays until the area is disinfected again.
Viruses are interesting because they push at the boundaries of what we mean by "life". On their own, they are just rather complex chemicals (some can even be crystallised), not showing any of the common life signs, such as metabolism, growth, reproduction or response to stimuli. Only by infecting a cell can they become active and reproduce. Coronaviruses consist of a strand of genetic material (RNA), wrapped in a protein coat, covered in an lipid bilayer envelope. The genetic material will take over the host cell's machinery to make copies of itself, and the protein coat and envelope are there to protect the genetic material and deliver it into a suitable host cell.
This has an important consequence for control: viruses are only diluted or destroyed in the environment. This is in contrast to many other disease-causing organisms, that can find niches and reproduce outside their hosts. For example, Vibrio cholerae causes cholera in humans, but it also lives and reproduces in brackish or salty water.
Viruses also tend to be specific in their host. The protein coat (and, in coronaviruses, the envelope) has specific features that facilitate it attaching to and delivering its genetic payload to cells of the usual host. There are unusual events, where a virus crosses a species boundary and starts to infect a different host, and this is believed to have happened for COVID-19, possibly from bats, to humans.
What is a virus to, say, a bacterium that isn't its host? Well, it's a package of fat, protein and sugar, and therefore, quite possibly, food.
Bring On The Yoghurt
Many microorganisms, including bacteria and fungi (such as yeast), live by scavenging whatever they can find and process in their environment. Different species of microorganism may be better or worse at processing different foodstuffs: yeast consume sugar, but cannot cope with starch, which is why grain is malted before brewing. They may produce waste products that they tolerate, but kill other microorganisms, such as yeast producing alcohol, or Lactobacillus producing lactic acid. A mixture of microorganisms may form a biofilm where they may cooperate to process an increased range of foods.
Rather than relying on frequent disinfection to deactivate coronavirus in the environment, would it be possible to encourage the growth of biofilms that would deactivate (eat) the virus faster, and have a continuous effect?
What would be the desirable characteristics of microorganisms in this biofilm? First, that they are not pathogens. It would not be a good idea to spray door handles with salty water full of Vibrio cholerae, even if it were proven that it would efficiently eat the coronavirus. Lactobacillus might be a good organism to try first: it is not a pathogen, and is known to inhibit the growth of some pathogens, and it is readily available and familiar to many people in yoghurt.
The second desirable characteristic would be, of course, that it eats the coronavirus. This is unknown. More research is required.
In the future, will a yoghurt-covered door handle be a safe door handle?