ReviewGut microbiota and Covid-19- possible link and implications
Introduction
Coronavirus disease 2019 or Covid-19 is a new public health crisis threatening the humanity. Although, it originated in the Hubei province of China in late 2019 yet it has spread to many countries in the world (Wang et al., 2020). This pandemic disease is caused by the novel betacoronavirus, now named SARS-Cov-2(Lake, 2020). Covid-19 has very important clinical features such as high rates of transmission, mild to moderate clinical manifestation with more serious radiological abnormalities seen in the elderly (Yuen et al., 2020).
Coronaviruses are positive sense RNA viruses with spike like projections on its enveloped surface giving it a crown like appearance hence the term Coronavirus (Singhal, 2020). Phylogenetic diversity studies have highlighted that SARS-Cov-2 shares 79% nucleotide sequence identity with another virus of the same family SARS-Cov which caused major epidemic in 2002–2003 that resulted in 8000 cases in 26 countries (De Wit et al., 2016). Additionally, SARS-Cov-2 also displays sequence identities of 96% and 89.6%, for the envelope and nucleocapsid proteins respectively with SARS-Cov (Zhou et al., 2020b). Middle East respiratory syndrome or MERS disease in 2012 was also caused by another coronavirus called MERS-CoV. All these viruses utilize the ACE-2 receptor for their cellular entry (Zhou et al., 2020a). Interestingly, ACE-2 receptors are also reported to be expressed in the kidney and gastrointestinal tract, tissues known to harbour SARS-CoV (Harmer et al., 2002; Leung et al., 2003). Earlier evidence suggested that SARS coronavirus viral RNA was detectable in the respiratory secretions and stool of some patients after onset of illness for more than one month but live virus could not be cultured after third week (Chan et al., 2004). Now, recent report also suggests that SARS-Cov2 RNA can be detected in stool of some patients of Covid-19 (Wu et al., 2020). This along with the fact that some patients of this disease have diarrhoea points out towards a distinct possibility of involvement of gut-lung axis and may be the gut microbiota (Chan et al., 2020).
Section snippets
Gut microbiota and the gut-lung axis
The human gut microbiota consists of 1014 resident microorganisms which include bacteria, archae, viruses and fungi (Gill et al., 2006). Primarily, the gut bacteria in healthy individuals is dominated by four phyla Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes (Villanueva-Millán et al., 2015). The colon harbours an extremely high density of bacteria in the families Bacteroidaceae, Prevotellaceae, Rikenellaceae, Lachnospiraceae and Ruminococcaceae (Hall et al., 2017). The gut
Nutrition and gut microbiota – strengthening the reservoir
Diet plays an important role in shaping the composition of the gut microbiota thereby influencing the host’s health status. Various diet forms are found to influence the specific compositional patterns of the gut microbiota like, for e.g., the different composition of the microbiota with animal fat and protein-based diets versus vegetable-based diets has been reported (De Filippis et al., 2016). It is interesting to note that the gut microbiota of animals fed with a high fat or high sugar diet
Conclusion and future perspective
Covid-19 has pushed the world to the brink. The faster we understand this disease the better we will be prepared the next time. Research in gut microbiota has propelled our knowledge in the field of chronic and infectious diseases. The presence of SARS Cov2 RNA in the stool of some patients and diarrhoea in few suggest a subtle link between the lung and the intestine. Although, no faecal-oral transmission is reported, yet it can be assumed that many asymptomatic children and adults may shed
Declaration of Competing Interest
Debojyoti Dhar is the Director of Leucine Rich Bio Pvt Ltd.; There is no financial disclosure
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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