Gut microbiome, immune system and Covid-19

Despite the fact that SARS-CoV-2 is known to attack our respiratory system causing cough, shortness of breath and pneumonia, there have been cases of patients with gastrointestinal problems, like diarrhea, vomiting and abdominal pain. This means that the presence of virus receptors in gastrointestinal epithelial cells in combination with an imbalance in gut microbiome and a not so robust immune system can lead to complications when dealing with Covid-19. Furthermore, the risk of serious infection by Covid-19 is bigger among those who have high blood pressure, diabetes and obesity, conditions that are linked with changes in gut microbiome composition. This inevitably raises questions on whether our gut microbiome plays a role in the severity of Covid-19.

The symptoms of diarrhea, vomiting and abdominal pain that occur in some patients may originate not only from antibiotics given to deal with bacterial pneumonia, but also from the virus’ ability to infect the gut and reproduce in it. What’s more, the receptors used by SARS-CoV-2 to infect the host cells are found in the oral cavity, the esophagus, the stomach, the gut and in other organs like the kidneys, the gallbladder, the cardiac muscle, even the cerebellum.

There’s even a small series of cases that support the involvement of the gastrointestinal environment in Covid-19, in which some patients had imbalance in the microbiome composition, lacking in Lactobacillus and Bifidobacterium, which is certainly going to lead in greater research. 

Although the gut-lung axis isn’t something new and is already known in the progress of certain respiratory conditions, the respiratory symptoms, the gastrointestinal tropism of SARS-CoV-2 (which means that certain pathogens show preference to certain cells) and the alteration in gut microbiome in some cases, make scientist believe that gastrointestinal tract is a possible target when it comes to the disease’s management and transmission.

How can probiotics and prebiotics help
As far as the pandemic of the new coronavirus is concerned, there have been two meta-analysis that refer to the effectiveness of probiotics in reducing the frequency and duration of viral respiratory infections. Not long ago, the National Health Commission in China and the National Administration of Traditional Chinese Medicine recommended probiotics in cases of patients with severe symptoms of Covid-19 in order to help prevent a secondary bacterial infection. All these are certainly preliminary findings, but may light the path to move forward in research on probiotics and the prevention of pneumonia.

On prebiotics, research has shown that inulin supplementation -which is a type of soluble fiber- for 8 weeks has led to greater levels of CD8+T cells in the lungs of rats (which are cells that are protective against viral infections, important for immune defense) that have been infected with Influenza A virus. These supplements in rats showed lower viral load of the flu and raised survival. So what we need to see here is to what extend consumption of foods rich in soluble fiber might improve recovery.

Up to now, the available data show that infection with SARS-CoV-2 moves beyond the lungs and can affect, apart from the immune system, the gastrointestinal system also. Although we need more research before suggesting probiotics and prebiotics in patients with Covid-19, studying the gut microbiome and gastrointestinal system in controlling the virus can offer a valuable approach.