Words by: Joe Kleinschmidt

With the outbreak of the Coronavirus epidemic, information and misinformation about avoiding infectious diseases has been widely circulated on and offline. Even from apparently reputable sources, a surprising amount of advice does not hold up to research. In this article, we examine some of the myths and realities of catching a cold, flu, or even the novel 2019 Coronavirus, as well as some of the more interesting facts about the world of microorganisms around us.

How do viruses and bacteria spread?

Contracting a viral or bacterial infection is remarkably difficult – a special set of circumstances must be present. Your skin normally presents a totally impermeable barrier for viruses and other microorganisms. In order to enter your body, a microorganism must come into contact with the areas of the body where living cells are exposed to external material. In an uninjured person, this is usually the digestive tract, the respiratory tract, or the eyes.

Coronavirus is usually contracted via the lungs. Therefore, the virus must be present in the air in the form of tiny microscopic droplets which are normally produced when a person sneezes or coughs. The typical range from which a person could be infected is 6 to 10 feet (2 – 3 metres). The WHO has also stated that unless a person is showing symptoms, such as cough and diarrhoea, they are unlikely to be infectious.

Each morsel of food you eat contains millions of bacteria and viruses. But to enter the digestive tract, a virus or bacterium must pass through the stomach – where a highly acidic environment will usually cause death or inactivation. Furthermore, most of the bacteria and viruses in the environment are harmless.

After surviving the stomach, a virus or bacterium would still need to pass through the mucus lining of the intestines, and enter directly into a cell, avoiding destruction by the mucus itself and immune cells. Ultimately, this means that contracting the novel Coronavirus by ingesting food is unlikely.
However, new evidence has suggested that faeces from an infected person can release viral particles. As with food consumption, kissing is actually a relatively safe when it comes to infection from a loved one with a cold or flu – as confirmed, for example, in a bizarre study from 1984, which
found that the common cold (caused by Rhinovirus) only infected one out of thirteen people exposed through contact with their partner’s mouth.

Unfortunately, many diseases caused by consumption of contaminated foods do not result from live bacteria or viruses, but rather toxins produced by bacteria, such as Botulinum toxin. These toxins, usually produced by bacteria in food which has been left in warm, wet conditions for prolonged periods, often cannot be inactivated by cooking, or stomach acid. Many cases of such food poisoning have been reported amongst students consuming leftover unrefrigerated food.

How does the novel coronavirus epidemic compare to other epidemics?

The fact that new viruses and bacteria can evolve at any time is often forgotten. The collapse of many major civilisations, such as the Roman Empire, has been attributed to the evolution of new microorganisms and subsequent depopulation of cities. The Spanish flu epidemic of 1918 has been estimated to have killed 50 to 100 million people, and infected approximately one quarter of the world’s population, despite the major advances made in public health over the preceding decades. But all recent viral epidemics, including the SARS epidemic a decade ago, have been safely contained through simple measures such as quarantining and enhanced hygiene measures. The spread of new epidemic diseases has been mainly confined to countries with poor public health infrastructure.

Could the novel Coronavirus evolve to become more dangerous?

A virus or bacterium which has a high mortality rate tends to have a low transmission rate, because patients become ill quickly and cannot spread the disease. Therefore, there is a balance between infectiousness and morbidity (the degree to which the microorganism causes disease). This tends to limit the outbreak of any infectious disease.

What conditions will inactivate a virus or bacterium?

While some viruses and microorganisms can survive harsh conditions, most – including coronavirus –are quite fragile. At normal body temperatures, a recent study found that levels of active viral particles of the SARS-Coronavirus (which is highly similar to the 2019 novel Coronavirus) were undetectable following one hour incubation at a pH of 3 (a lower pH indicates higher acidity). The acidity of the stomach is usually stronger than this. Similarly, 15 minutes of heating at 75° C was extremely effective at inactivating the virus.

How long can infectious bacteria and viruses like the novel Coronavirus survive outside human bodies?

There is debate over the extent to which the novel 2019 Coronavirus can persist on external surfaces and remain infectious, but the maximum length of time the virus may survive in the environment is estimated at a few hours. This means that this is unlikely to be the main route of transmission, and secondly, goods exported from China or other countries with cases of Coronavirus will not contain active viral particles.

Does handwashing kill bacteria and viruses?

Although soap itself does little to kill bacteria or viruses, it does help to remove the vast majority of present on hands and lowers the odds of contracting an infection after touching your eyes.

Can some bacteria and viruses survive more extreme environments?

Some more unusual bacteria and viruses appear to be extremely tough. In particular, particles known as endospores, which are dormant versions of bacteria which can reactivate to form a living bacterium, can survive very severe environments, and remain active for tens of millions of years. Likewise, spores of the Bacillus strain have been shown to be viable after heating up to 420° C. Some have even suggested that these microorganisms may have been able to survive a journey into outer space on a meteorite leaving Earth, potentially allowing life to have colonised other planets.

Image Credit: Dr. Fred Murphy

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