Alteration of Gut Microbiota Affects the Severity and Complications of COVID-19

Research shows that depletion of certain types of bacteria in the gut lead to more severe cases of COVID-19, while the presence of others boosts immunity.

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Increasing evidence suggests that alterations in the gut microbiota are associated with the development, severity, and sequelae of COVID-19 infection.

In the adult digestive tract, there are approximately 100 trillion microbes, 10 times the number of human cells, and they weigh about 4.41 pounds. These organisms are immune system guardians and can help remove viruses.

Certain Gut Bacteria Can Inactivate COVID-19 Virus

In a new study published in Cell Host & Microbe, researchers evaluated the impact of gut microbiota composition on respiratory viral infections through animal experiments. The results showed that segmented filamentous bacteria (SFB) in the gut could protect mice from viral influenza, respiratory syncytial virus (RSV), and the COVID-19 virus.

Studies have indicated that SFB, whether naturally present or acquired, can combat viral infections with the help of alveolar macrophages in the lungs.

Alveolar macrophages serve as the first line of defense against respiratory pathogens.

In mice that don’t have SFB, these immune cells were rapidly depleted as infection progressed. Conversely, in mice with SFB in the gut, these immune cells underwent alterations to resist the inflammatory signaling induced by the influenza virus. Moreover, alveolar macrophages directly disabled the influenza virus.

Gut-Lung Axis

While the functions of the gut and lungs are different, they share common structural features, as they both develop from the same embryonic tissue. Both the gut and lungs are covered with mucous membranes. These membranes secrete mucin and collectively form a mucosal immune system that defends against pathogens.

As research on COVID-19 progresses, some researchers have noted the bidirectional and complex relationship of the gut-lung axis. Microbiota-derived metabolic pathways can function distally and play a vital role in anti-inflammatory responses in the airways.

The SFB are unlikely to be the only kind of gut microbe capable of affecting the immune cells in the lungs, said Dr. Andrew Gewirtz, a co-senior study author, in a press release.

Dr. Richard Plemper, a co-senior author of the paper, said that among the thousands of microbial species inhabiting the mouse gut, a common commensal microbe significantly impacted respiratory virus infections. He further stated that if these findings apply to human infections, they could have substantial implications for the risk assessment of disease progression in patients.

Research has shown that alterations in the gut microbiota, including changes in specific microbiota species and microbial-derived metabolites, play an important role in regulating the severity and progression of COVID-19 infection and post-recovery complications.

Viral Respiratory Tract Infection Affects the Gut Microbiota

An analysis of fecal samples from 102 patients with severe COVID-19 infection following ICU admission found that decreased concentrations of gut microbiome metabolite—secondary bile acids and desaminotyrosine—were associated with an increased risk of respiratory failure and mortality.

Another study revealed that patients infected with COVID-19 showed a decrease or depletion of bacteria with immune-regulating capabilities in the body, such as Faecalibacterium prausnitzii, as well as some bacteria from the Lactobacillus and Bifidobacterium families.

Additionally, respiratory virus infections are often observed in patients undergoing hematopoietic stem cell transplantation. Microbiota analysis of these patients showed that those with reduced levels of commensal bacterial species producing butyrate had a fivefold increase in the progression of viral respiratory tract infections.

Enhancing Gut Health to Build Robust Immunity

The intestinal tract, the largest immune organ in the human body, plays a crucial role in establishing and maintaining a robust immune system, and gut immunity is closely linked to our diet.

Probiotics are beneficial bacteria for the gut and are relatively safe health supplements. A retrospective cohort study showed that COVID-19 patients treated with probiotics had a shorter time to clinical improvement, including reduced fever, hospital stays, and viral shedding. Another study also indicated that probiotic treatment significantly shortened the duration of diarrhea in critically ill COVID-19 patients.

BMJ Nutrition, Prevention & Health published a study in 2021 analyzing the effects of dietary habits on COVID-19 infection, severity of symptoms, and duration of the illness.

The study covered 2,884 frontline health care workers from six different countries, investigating their dietary habits and the severity of COVID-19 infection. The results showed that participants who followed either a plant-based or pescatarian diet (where a person doesn’t eat meat but eats fish) had a 59 percent lower odds of developing moderate to severe COVID-19 than those who did not.