Cytokine storm is one of the characteristics of severe SARS-CoV-2 infection. A recent study reported that gut microbes may play a role in severe COVID-19 infection. It has been proven before that SARS-CoV-2 infects intestinal tissue. Viral RNA has been found in feces for over 30 days. Gut microbiota is vital for many body functions such as immune regulation. Inflammatory conditions have been linked to the unbalanced gut microbiome. The virus could lead to abnormal inflammatory reactions that could worsen COVID-19.
The study examined IgA levels, which is the most abundant immunoglobulin in humans. The study also evaluated that hoe gut microbiota is altered in this condition and how is it related to anti-SARS-CoV-2-IgA and IL-18. The study included 33 patients with seasonal influenza, 62 COVID-19 patients and 40 healthy patients. Serum and fecal sample analysis revealed that the COVID-19 patients were less diverse than other patients.
The genera Bifidobacterium, Lactobacillus, Clostridium, and Streptococcus were overexpressed. The genera Parabacteroide, Coprococcus, Bacteroidetes, Roseburia, and Faecalibacterium were fewer as compared to healthy controls. In patients with seasonal influenza, the genera Sutterella and Parabacteroides were underrepresented in COVID-19 patients, but the genera Escherichia, Streptococcus, Fusobacterium, Veillonella, Clostridium, and Bifidobacterium were increased. Thus increase in the expression of Streptococcus in COVID-19 patients increases the risk of opportunistic infections. IgA was significantly elevated in COVID-19.
However, fecal samples did not show significant differences in the specific IgA levels between COVID-19 and control groups. This indicates that the mucosal infection probably occurred in the respiratory tract and not the gut. IL-18 levels in COVID-19 patients were higher indicating that the virus-induced inflammation in the gut. The fecal IL-18 levels were elevated when the genera Citrobacter, Peptostreptococcus, and Fusobacterium were overexpressed. This suggests that IL-18 can be used as an indicator of intestinal infection in COVID-19 patients. Gut microbiota dysbiosis is an indicator of COVID-19 disease severity.
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