Abstract
High expression of the transmembrane protein angiotensin I converting enzyme 2 (ACE2), more than 100-times higher as in the lung, and transmembrane serine protease 2 (TMPRSS2) in the gastrointestinal tract leads to infection with SARS-CoV-2. According to meta-analysis data, 9.8–20% of COVID-19 patients experience gastrointestinal symptoms, where diarrhoea is the most frequent, and about 50% shed viruses with high titre through their faeces, where a first faecal transmission was reported. Furthermore, gut inflammation, intestinal damage, and weakening of the gut mucosal integrity that leads to increased permeability has been shown in different studies for COVID-19 patients. This can lead to increased inflammation and bacteraemia. Low mucosal integrity combined with low intestinal damage is a good predictor for disease progression and submission to the intensive care unit (ICU). Several pilot studies have shown that the gut microbiome of COVID-19 patients is changed, microbial richness and diversity were lower, and opportunistic pathogens that can cause bacteraemia were enriched compared to a healthy control group. In a large proportion of these patients, dysbiosis was not resolved at discharge from the hospital and one study showed dysbiosis is still present after 3 months post COVID-19. Consequently, there might be a link between dysbiosis of the gut microbiome in COVID-19 patients and chronic COVID-19 syndrome (CCS). Various clinical trials are investigating the benefit of probiotics for acute COVID-19 patients, the majority of which have not reported results yet. However, two clinical trials have shown that a certain combination of probiotics is beneficial and safe for acute COVID-19 patients. Mortality was 11% for the probiotic treatment group, and 22% for the control group. Furthermore, for the probiotic group, symptoms cleared faster, and an 8-fold decreased risk of developing a respiratory failure was calculated. In conclusion, evidence is arising that inflammation, increased permeability, and microbiome dysbiosis in the gut occur in COVID-19 patients and thus provide new targets for adjuvant treatments of acute and chronic COVID-19. More research in this area is needed.
Highlights
With nearly 200 million confirmed cases and more than 4 million deaths (WHO, July 2021), the COVID-19 pandemic has had a huge impact on our society, economy, and way of life
It has been shown that SARS-CoV-2 infection alters the microbiome of the lung and leads to reduced diversity and in some cases to community collapse [61], shows different bacterial diversity and fewer commensals compared to non-COVID-19 pneumonia [62], and on a functional analysis “decreased potential for lipid metabolism and glycan biosynthesis and metabolism pathways, and increased potential for carbohydrate metabolism pathways” [63]
SARS-CoV-2 is infecting the gut in a portion of COVID-19 patients, as about 20%
Summary
With nearly 200 million confirmed cases and more than 4 million deaths (WHO, July 2021), the COVID-19 pandemic has had a huge impact on our society, economy, and way of life. Since the discovery of COVID-19/SARS-CoV-2 in December 2019, a staggering 1,608,720 scientific articles are available on PubMed (28 July 2021). Variants of SARS-CoV-2 are a potential threat and other treatment options would still be advantageous. In this review, the focus is on the infection of the gut by SARS-CoV-2 and possible treatment and prevention options. To present this in context, the interaction of SARSCoV-2 with the gastrointestinal tract will be briefly introduced, including gastrointestinal symptoms, shedding of the virus in stool, probability of faecal transmission, expression of receptor and host protease, inflammation, changes in mucosal integrity, and dysbiosis in the gut microbiome. In an opinion paper by the same author, the connection between changes in the gut microbiome and chronic COVID-19 syndrome (CCS) is discussed in detail [1]
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