Microbiota Dysbiosis and Serotonin Dysregulation Linked to Long COVID Gastrointestinal Symptoms

Medical News: Recent research is shedding light on why some people continue to suffer from gastrointestinal (GI) issues long after recovering from COVID-19. This study, conducted by researchers from National Taiwan University College of Medicine, explores how disruptions in gut bacteria and serotonin regulation could be driving long-lasting bowel symptoms for many COVID survivors.

Graphical Abstract: Microbiota Dysbiosis and Serotonin Dysregulation Linked to Long COVID Gastrointestinal Symptoms

The Lingering Effects of COVID-19 on the Gut
COVID-19, caused by the SARS-CoV-2 virus, has primarily been known as a respiratory illness. However, it’s now clear that the virus can affect much more than just the lungs. Many patients experience gastrointestinal symptoms during the acute phase of COVID-19, such as nausea, diarrhea, and stomach pain. For some, these symptoms persist long after the virus is gone, a condition referred to as long COVID.
 
This Medical News report discusses new findings suggesting that long COVID may trigger gut-related issues by disrupting the balance of bacteria in the intestines (microbiota dysbiosis) and interfering with serotonin levels, a crucial neurotransmitter that helps regulate bowel movements. The study builds on evidence that the virus may continue to affect the gut even after it has been cleared from the respiratory system.
 
Viral Shedding in the Gut: A Key Factor
The research team, led by Professor Linda Chia-Hui Yu from National Taiwan University, found that SARS-CoV-2 can persist in the intestines long after it has left the lungs. This intestinal viral shedding may be a driving force behind the ongoing bowel issues seen in long COVID patients. Even after recovering from respiratory symptoms, many patients still test positive for the virus in fecal samples, suggesting that the virus can linger in the gut.
 
The study found that between 40% and 85% of patients had traces of the virus in their feces. Notably, those who had gastrointestinal symptoms during their COVID infection were more likely to test positive for viral shedding in the gut, even months after their respiratory symptoms cleared. This persistence of the virus could be contributing to the dysbiosis, or imbalance, in gut bacteria.
 
The Role of Microbiota Dysbiosis and Serotonin in Long COVID
Healthy gut function relies on a balanced community of bacteria, viruses, and fungi - collectively known as the microbiome. When this balance is disrupted, it can lead to a range of digestive problems, including symptoms similar to irritable bowel syndrome (IBS). The researchers propose that SARS-CoV-2 may upset this delicate balance by altering the gut virome (the collection of viruses in the gut), leading to long-term disruptions in gut health.
 
In particular, the study highlights the role of serotonin, a neurotransmitter that helps regulate gut movement. Most of the body’s serotonin is produced in the intestines, not the brain. The research suggests that disrup tions in serotonin production, caused by changes in the gut microbiome, may lead to nerve hypersensitivity in the intestines, resulting in pain and changes in bowel habits. This serotonin dysregulation could be a key factor in the development of post-infectious IBS symptoms in long COVID patients.
 
Long-Term Consequences of Gut Inflammation
The study also sheds light on how inflammation in the gut may play a role in long COVID symptoms. COVID-19 is known to cause a strong immune response, which can result in damage to the gut lining. This damage, in turn, allows harmful bacteria to cross into the bloodstream, potentially triggering further inflammation and worsening gut symptoms.
 
Patients with long COVID who experience gastrointestinal issues often have higher levels of inflammatory markers in their blood and stool, suggesting that the immune system is still active long after the initial infection. This ongoing inflammation may contribute to the persistent gut issues seen in long COVID.
 
A Closer Look at the Microbiome
By analyzing fecal samples from COVID-19 patients, the research team discovered significant changes in the composition of gut bacteria. Patients with long COVID showed lower levels of beneficial bacteria, such as Faecalibacterium prausnitzii, and higher levels of harmful bacteria like Ruminococcus gnavus. These bacteria are known to be associated with IBS and other gastrointestinal disorders.
 
Interestingly, the study also found changes in the gut virome. Patients with long COVID had higher levels of bacteriophages (viruses that infect bacteria) and other viruses, further supporting the idea that viral shedding in the gut could be a key factor in microbiota dysbiosis.
 
Serotonin and Nerve Sensitivity
One of the most intriguing findings of the study was the link between gut bacteria and serotonin. In healthy individuals, the gut bacteria help regulate serotonin production, ensuring smooth bowel movements. However, in patients with long COVID, disruptions in the gut bacteria may lead to an overproduction of serotonin, causing hypersensitivity in the intestines.
 
This increased sensitivity, known as visceral hypersensitivity, is a hallmark of IBS. It may explain why long COVID patients often report abdominal pain and changes in bowel habits, even months after recovering from the respiratory symptoms of COVID-19.
 
Implications for Treatment
The study’s findings have important implications for the treatment of long COVID. By better understanding the role of the microbiome in gut health, researchers may be able to develop new therapies aimed at restoring the balance of gut bacteria and reducing inflammation. Probiotics, prebiotics, and dietary changes could play a role in helping long COVID patients manage their gastrointestinal symptoms.
 
Additionally, targeting serotonin pathways with medications that regulate serotonin levels could offer relief to patients suffering from post-infectious IBS. These therapies, combined with efforts to reduce gut inflammation, may help improve the quality of life for long COVID patients.
 
Conclusion
The findings of this study offer important insights into the gastrointestinal effects of long COVID. By identifying a link between microbiota dysbiosis, serotonin dysregulation, and ongoing bowel symptoms, the researchers have paved the way for new treatments that could bring relief to millions of people worldwide. Restoring gut health through microbiome-targeted therapies and regulating serotonin levels may hold the key to alleviating long COVID’s lasting impact on the gut.
 
The study findings were published in the peer-reviewed journal: Life Sciences.
https://www.sciencedirect.com/science/article/pii/S0024320524007434
 
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