Updated: Jun 26, 2020
Sars-CoV-2: the strain of coronavirus that causes COVID-19
COVID-19: the disease (and its symptoms) caused by Sars-CoV-2
Nearly 2500 years ago the ancient greek physician Hippocrates said "All Disease Begins in the Gut"
His observation is not entirely correct, but it's also not entirely incorrect.
Today, the gut is becoming increasingly significant in the wake of our advanced understanding of various diseases.
Gut Microbiota "The forgotten Organ"
The microbiota comprises all the microscopic organisms living in or on our body. In a 70 kg "reference man" this is about 38 trillion microorganisms.
The largest reservoir of microorganisms lives inside our digestive system. Collectively, they're known as the gut microbiota. The terms gut microbiota and gut bacteria are often used interchangeably because bacteria make up about 90% of the microbiota.
Relatively few bacteria are present in the stomach and small intestine. The colon, in contrast, contains the highest microbial density recorded in any habitat on Earth with bacteria from over 1000 different species - good and bad.
Examples of good bacteria are bifidobacterium and lactobacillus, which are found in most probiotic products.
The gut microbiota exhibits a huge diversity and individuality, being shaped by factors such as your genetics, gender, age, immune system, disease condition, medical treatments, geographic and socio-economic environment, diet, etc.
The Gut Microbiota and the immune system
The immune system and the gut microbiota co-evolve as they mature. Together they learn to recognise and tolerate good microorganisms, but also learn to recognise and initiate a defensive response against pathogens (bad microorganisms).
The gut is your largest immune organ, home to 70% of your immune cells
This team-work between the gut microbiota and immune system helps to maintain gut health as well as overall health.
But if either the immune system or gut microbiota are disrupted (dysbiosis), the whole balance is compromised.
Animal studies have shown that mice with dysbiosis or no gut microbiota have an impaired immune system and a heightened sensitivity to pathogens.
The Gut and COVID-19
The link between the risk of COVID-19 and the gut microbiota is based on the active cross-talk between the lung and the gut microbiota, known as the gut-lung axis.
The gut-lung axis hypothesises that lung disease can disrupt the gut microbiota and in turn, alterations of the gut microbiota can affect the development (or pathogenesis) of lung diseases
This has been observed in pneumonia and influenza.
Many scientists are tempted to believe the same applies for Sars-CoV-2. They believe Sars-CoV-2 can disrupt the gut microbiota, which then exacerbates the pathogenesis of COVID-19.
Scientific and clinical observations both support this:
Studies in gut organoids (miniaturised organs) show that coronavirus directly infects the gut lining because the receptors which the virus attaches to in our bodies - Angiotensin Converting Enzyme 2 or ACE2 - is present in our lungs and our gut
Clinical data shows that more than 60% of patients with COVID-19 have diarrhoea, nausea, and vomiting and more importantly, gastrointestinal symptoms in COVID-19 are associated with prolonged symptoms and increased severity
A healthy and happy gut microbiota could be pivotal in maintaining the balance and control of the immune system to fight COVID-19 and even prevent a deadly cytokine storm (the destructive over-reaction of the immune system).
This is especially relevant in elderly patients or patients with co-morbidities like diabetes whose gut microbiota is already compromised (e.g. due to inflammation or an unbalanced diet). These patients have a very different gut microbiota compared to healthy adults and children. They have less diversity and a lower proportion of good bacteria, due to lifestyle, diet, lesser mobility, weakened immune system, use of medications, etc.
A healthy diet and gut microbiota cannot protect you from the Sars-CoV-2 virus. However, studies suggest that it can be prophylactic and improve clinical outcomes for COVID-19.
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