The sudden and rapid outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the pandemic of coronavirus disease 2019 (COVID-19), which has claimed more than 6.3 million lives worldwide the world on June 7, 2022. the high rate of genomic mutation, several variants of SARS-CoV-2 have emerged, which have been categorized as variants of concern (VOC) and variants of interest (VOI).
Researchers have reported that SARS-CoV-2 affects many organs, including the lungs, stomach and heart of infected patients. In a recent virus review article, scientists discuss the gastrointestinal (GI) complications associated with COVID-19.
Study: Gastrointestinal involvement in SARS-CoV-2 infection. Image credit: Kateryna Kon / Shutterstock.com
SARS-CoV-2 infection and gastrointestinal complications
Several studies have reported that SARS-CoV-2 is primarily targeted at lung cells, causing significant respiratory complications. Interestingly, many studies have also reported the presence of SARS-CoV-2 ribonucleic acid (RNA) in stool samples from infected patients, thus confirming the elimination of SARS-CoV-2 in feces.
Some of the common gastrointestinal complications associated with COVID-19 include vomiting, anorexia, nausea, and diarrhea. SARS-CoV-2 infection with gastrointestinal symptoms can lead to an acute infection with a poor prognosis.
Gastrointestinal imaging in patients with COVID-19 has provided evidence of intestinal wall thickening, mesenteric thickening, fluid-filled large intestine, hyperemia, pneumatosis, and ischemia on rare occasions. Previous studies have also reported that diarrhea caused by SARS-CoV-2 infection could be due to malfunction of intestinal ion transporters causing inflammation and various gastrointestinal complications.
It is important to note that patients with COVID-19 who experience gastrointestinal symptoms are more likely to develop severe respiratory distress. Scientists have speculated that inflammatory cytokines may be the possible link in the pathogenesis of SARS-CoV-2 between the respiratory and digestive systems.
Gastrointestinal-pulmonary axis in COVID-19. ACE2, angiotensin converting enzyme 2.
In addition, patients with acute COVID-19 experience more abdominal pain than patients with mild symptoms. However, not many differences have been reported in terms of loss of appetite, vomiting, diarrhea, and nausea symptoms reported in both patient groups.
Patients with thromboembolic events and gastrointestinal disorders such as mesenteric ischemia have a high risk of mortality. In addition, the level of transaminases in patients with COVID-19 is usually very high, which causes intestinal ischemia and increases the risk of intestinal obstruction.
Previous studies have also indicated that SARS-CoV-2 virions can enter the gastrointestinal tract through the esophagus. In addition, the detection of SARS-CoV-2 in the feces of infected patients implies that the virus has been transmitted by fecal-oral route. Taken together, endoscopic sampling of the gastrointestinal tract of a patient with COVID-19 has revealed the presence of SARS-CoV-2 RNA in the stomach, esophagus, rectum, and duodenum. SARS-CoV-2 (N) nucleocapsid protein 2 has also been detected in the cytoplasm of rectal glandular epithelial cells and duodenal cells.
SARS-CoV-2 and the intestinal microbiome
The presence of virus in the gastrointestinal tract influences the health of the hosts, as the virus interacts with the mucus layers, the immune cells of the lamina propria and the epithelial cells. In addition, alterations in the intestinal viroma can have a significant impact on the immunophenotype.
The intestinal microbiome is rich in beneficial bacteria that are responsible for maintaining intestinal homeostasis, suppressing excessive mucosal inflammation, and facilitating the development of immune responses on mucosal surfaces. Altogether, the intestinal microbiota consists of approximately 100 trillion microorganisms and thousands of bacterial species.
Adaptive and innate immune cells are triggered by disruption of the integrity of the intestinal barrier. In addition, the release of proinflammatory cytokines into the circulation can lead to systemic inflammation. Thus, the entry of inflammatory cells such as neutrophils and lymphocytes into the intestinal mucosa can cause severe disruption of the intestinal microbiota.
A change in the composition of the intestinal microbiome, ie an increase in Campylobacter, Parabacteria, Bacteroides, Bifidobacterium, Clostridium, Ruminococci, Rotella, Corynebacterium Pseudomonas, Enterococcus and Aspergillus, and a considerable reduction in Eubacterium, Faecalibacterium, and L. , influences the results of COVID-19. An earlier study indicated that alterations in the composition and function of the intestinal microbiome affect the respiratory tract through the immune system of the common mucosa. Respiratory dysbiosis also influences the digestive tract through immune regulation.
SARS-CoV-2 elicits early neutralizing antibody responses, including peripheral expansion of immunoglobulin A (IgA) plasmablasts with mucosal homing potential, systemic IgA, and systemic IgG. An earlier study reported that the intestinal-lung axis plays an important role in the control of COVID-19.
Another study found that cytokines could enter the lungs through the bloodstream when the gut is inflamed. This condition significantly affects the lung immune responses and inflammation.
An increase in circulating proinflammatory cytokines could also affect the composition of the intestinal microbiome which in turn could improve intestinal permeability. This can lead to the translocation of pathogens and toxins and, as a result, increase the severity of the disease and cause multiple organ failure.
An altered intestinal microbiome and epithelial inflammation could also improve the expression of the angiotensin 2 converting enzyme (ACE2) receptor in the gut, which SARS-CoV-2 primarily uses to enter cells.
Overall, the exact underlying mechanisms associated with common gastrointestinal symptoms and COVID-19 remain largely unknown.
Some patients with COVID-19 suffer from gastrointestinal symptoms; however, these off-target symptoms in SARS-CoV-2 infected patients are often overlooked. In the future, GI symptoms and changes in the intestinal microbiota of patients with COVID-19 should be studied, as targeting these tissues may be effective in controlling infection.
- Chen, HT, Hsu, M., Lee, M., et al. (2022) Gastrointestinal involvement in SARS-CoV-2 infection. Virus 14 (6). doi: 10.3390 / v14061188.