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How does Covid-19 infection work?

We are neither doctors nor virologists, our scientific team is simply trying to summarise research that appears to explain what the Covid-19 infection is and how it works.

Is Covid-19 a new virus?

Covid-19, also called SARS-CoV-2, belongs to the beta-coronavirus family.1 However, the viruses within this group can vary significantly from one another as they mutate very quickly. Covid-19 is sufficiently different from SARS-CoV, which appeared in the early 2000s (21% different), and from MERS-CoV (50% different) to not be recognised by our immune system.2 As a result, the immune system’s memory cells, explained here, are not activated to help the body fight the virus more quickly and effectively.

What is a virus and how is Covid-19 spread?

Measured in nanometres, a virus is a tiny collection of genetic material (in this case, RNA or ribonucleic acid), proteins and a lipid membrane. Viruses cannot reproduce on their own. Instead, they require a host cell, which they invade and force to mass-produce the different viral components, which then come together to form a new virus. Eventually, there are too many viruses and the host cell bursts or dies. The newly-formed viruses are then released to infect nearby cells, spreading the virus.

There is increasing evidence that Covid-19 is transmitted through droplets from coughing or sneezing that can travel up to several metres in the air and land on surfaces. The virus can survive on surfaces for many hours, depending on the material, and is transferred to our hands upon contact. Hands therefore serve as a means of transport for the virus. Up to this point, washing your hands properly with soap, which is more effective than alcohol-based hand sanitisers because it dissolves the lipid membrane to kill the virus3, can eliminate virus particles. The main concern lies in touching your face every few minutes and there is a high risk of infection as soon as there is contact with the respiratory tract or mucous membranes in the eyes and mouth.

What happens once a person is infected?

Scientists are studying what Covid-19 does to the body, however nothing has been confirmed yet. It has been reported that it may attach itself to ACE2 receptors, found in cells in the respiratory tract and lungs, as well as the liver, stomach, intestines and kidneys, in order to enter and replicate in our cells. Other co-receptors may also be involved.4

The immune system acts as soon as it detects the virus. Cells of the innate immune system (informative link) try to fight the virus. They do this by releasing toxic molecules as well as ‘eating’ (phagocytosis) and immobilising the infected cells.1 Macrophages (immune cells that engulf and digest infected cells) are thought to communicate with cells that have ACE2 receptors.4 Inflammatory molecules are also secreted to attract more immune cells to the lungs and combat the virus. After a week or so, cells of the adaptive immune system (informative link), including T cells and antibodies, join the battle.1 Having a fever is a sign that the body is starting to fight off the viral pathogens, which are often sensitive to heat. Coughing is also the body’s way of getting rid of the virus. Many people who get the infection display few or no symptoms and typically recover within two weeks.5

However, in some cases, the immune system cannot eliminate the virus and it travels down the respiratory tract to the lungs. Medical assistance is then required because the infection can cause potentially life-threatening respiratory problems, such as pneumonia or acute respiratory distress syndrome (ARDS).6 Difficulty in breathing means less oxygen enters the blood to be transported around the body, preventing the organs from getting the oxygen they need to function properly. Coronavirus can also damage the heart muscle in seriously ill patients.7,8 In these cases, patients need a ventilator and long-term care in an intensive care unit, often for more than 20 days.

Why are some people worse affected than others?

The World Health Organisation (WHO) has stated that those most at risk of Covid-19 are the elderly as well as people with underlying medical conditions, such as heart disease, lung disease or diabetes, and those who smoke. Factors related to lifestyle or genetics can also affect our immune response.

Although we do not understand why, it seems that many patients who experience symptoms have an immune system that responds less effectively to the virus, meaning a poor immune response, with fewer cells that are able to ‘patrol’ and act.9 An inadequate immune response can also cause persistent, chronic inflammation, which may lead to tissue fibrosis10 and cause cells and fluid to build up in the lungs, stopping them from working properly.1

What can be done?

There is currently no treatment or vaccine available. In order to stay healthy and stop the spread of coronavirus, thereby helping to flatten the curve to ease the pressure on hospitals and limit the number of deaths11, you must follow the guidelines : stay at home and avoid contact with others, cover your mouth and nose when you cough or sneeze, wash your hands regularly with soap and water and do not touch your face. It is important to remember that anyone can be an asymptomatic carrier of the virus. A hand-made tissue or paper towel mask can help to prevent people with the virus from infecting others, but it mainly stops you from touching your face. Leave medical masks for the people who need them the most, such as doctors, nurses and other caregivers.

If you have symptoms, self-isolate at home for at least 10 days. If you have a high temperature (38°C or above), the Swiss health authorities advise taking paracetamol as a precaution and do not recommend self-medicating with anti-inflammatory drugs.12  If you have difficulty breathing, stay at home and contact your doctor.

Certain nutrients have been found to help to maintain a normal immune system. However, there is no guarantee that they work, nor evidence that they help in case of Covid-19. To know more…

 

Swiss Alp Health Science Department, 31/03/2020

 

 

  1. Li, G. et al. Coronavirus infections and immune responses. Journal of Medical Virology 92, 424–432 (2020).
  2. Lu, R. et al. Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding. The Lancet 395, 565–574 (2020).
  3. Deadly viruses are no match for plain, old soap — here’s the science behind it – MarketWatch. Available at: https://www.marketwatch.com/story/deadly-viruses-are-no-match-for-plain-old-soap-heres-the-science-behind-it-2020-03-08. (Accessed: 30th March 2020)
  4. Qi, F., Qian, S., Zhang, S. & Zhang, Z. Single cell RNA sequencing of 13 human tissues identify cell types and receptors of human coronaviruses. Biochemical and Biophysical Research Communications (2020). doi:10.1016/j.bbrc.2020.03.044
  5. Coronavirus: What Happens To People’s Body If They Get Infected. Available at: https://www.webmd.com/lung/coronavirus-covid-19-affects-body. (Accessed: 30th March 2020)
  6. What happens to people’s lungs when they get coronavirus? | World news | The Guardian. Available at: https://www.theguardian.com/world/2020/mar/28/what-happens-to-peoples-lungs-when-they-get-coronavirus. (Accessed: 30th March 2020)
  7. Chen, C. et al. [Analysis of myocardial injury in patients with COVID-19 and association between concomitant cardiovascular diseases and severity of COVID-19]. Zhonghua xin xue guan bing za zhi 48, E008 (2020).
  8. He, X. W. et al. Impact of complicated myocardial injury on the clinical outcome of severe or critically ill COVID-19 patients. Zhonghua xin xue guan bing za zhi 48, E011–E011 (2020).
  9. Qin, C. et al. Dysregulation of immune response in patients with COVID-19 in Wuhan, China. Clinical Infectious Diseases (2020). doi:10.1093/cid/ciaa248
  10. Conti, P. et al. Induction of pro-inflammatory cytokines (IL-1 and IL-6) and lung inflammation by COVID-19: anti-inflammatory strategies. Journal of biological regulators and homeostatic agents 34, (2020).
  11. TRANSCEND MEDIA SERVICE » Coronavirus: The Hammer and the Dance. Available at: https://www.transcend.org/tms/2020/03/coronavirus-the-hammer-and-the-dance/. (Accessed: 31st March 2020)
  12. AINS et COVID-19 : évaluation pharmacologique.

 

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