Islet transplantation-immunological challenges and current perspectives

The gastrointestinal (GI) tract may be a significant entrance or interaction site for SARS-CoV-2; therefore, the gut mucosal immune system participates in virus interaction as a first-line physical and immunological defense, leading to GI involvement and symptoms. This review focuses on the GI symptoms associated with SARS-CoV-2 infection while providing specific results on variant-specific signs and syndromes related to coronavirus disease 2019 (COVID-19). The pattern of symptoms changed during the virus evolution, since the data provided a current and thorough picture of the symptoms experienced by SARS-CoV-2 infected people, and variations in symptom patterns occurred as the Alpha, Delta, and Omicron variants have spread. Since the beginning of the pandemic, GI symptoms have been linked to SARS-CoV-2 infections, even though most infected people do not report them. For example, diarrhea (28.2%) was the most frequently reported GI symptom in the early phase of the pandemic. The most observed GI tract symptoms during COVID-19 were anorexia (loss of appetite), nausea, vomiting, diarrhea, and abdominal pain, usually in at least one-third of the patients. Mesenteric ischemia and GI bleeding were less observed but more severe. While GI symptoms are not associated with increased mortality, they complicate the disease, increase the duration of the illness, and result in worse outcomes. Nevertheless, it is accepted that symptoms between variants differ significantly, i.e., the Omicron variant causes milder COVID-19 than the Delta. Still, the rate of GI symptoms has declined in the following variant-dominated phases of the pandemic (Alpha: 19.4%, Delta: 17.9%, Omicron: 13.8%), which was also demonstrated for other GI signs associated with COVID-19.