COVID-19, primarily recognized as a respiratory illness, can also significantly impact other bodily systems, including the digestive tract. Many individuals infected with SARS-CoV-2 experience nausea. This gastrointestinal symptom highlights the complex ways the virus interacts with the human body, and understanding its biological reasons clarifies the broader effects of the infection.
The Virus’s Direct Impact on the Digestive System
The SARS-CoV-2 virus can directly infect cells lining the gastrointestinal tract, contributing to digestive symptoms like nausea. This occurs because these cells, particularly in the small intestine, express angiotensin-converting enzyme 2 (ACE2) receptors. The virus uses these ACE2 receptors as entry points to invade the cells, similar to how it infects lung cells.
Once inside, the virus replicates within these intestinal cells, leading to cellular damage and inflammation. This disrupts normal gut function. These changes can manifest as various gastrointestinal symptoms, including nausea, vomiting, and diarrhea.
The Body’s Immune Response and Nausea
The body’s systemic immune response to SARS-CoV-2 infection also plays a role in causing nausea. When the immune system detects the virus, it releases signaling molecules called pro-inflammatory cytokines, such as IL-6 and TNF-alpha. These cytokines are part of the body’s defense mechanism.
These circulating cytokines can have widespread effects throughout the body, including influencing the brain’s vomiting center. They can also stimulate the vagus nerve, a major communication pathway between the gut and the brain. The resulting systemic inflammation can alter gut motility and function, contributing to nausea.
Brain-Gut Connections and COVID-Related Nausea
Nausea experienced during COVID-19 involves intricate neurological pathways, emphasizing the close communication between the brain and the gut, known as the brain-gut axis. The vagus nerve serves as a primary conduit, transmitting signals from the gastrointestinal tract to the brain. Direct viral effects on gut cells or the presence of inflammatory mediators can stimulate this nerve, sending signals that are interpreted as nausea.
The brain also has a specialized area called the chemoreceptor trigger zone (CTZ), which is sensitive to substances in the bloodstream. This zone, located outside the protective blood-brain barrier, can be activated by systemic inflammation or viral byproducts circulating in the blood. Activation of the CTZ sends signals to the vomiting center in the brainstem, leading to the sensation of nausea. The body’s stress response and anxiety further influence this brain-gut connection, worsening nausea.