Epidemiological studies either peer back into time looking for patterns or arrange monitoring of future variables looking for the same patterns. Data is analyzed and … sometimes nothing. When a pattern does arise out of the fog, they then have to go searching for biological links. Patterns may only indicate correlation but not causation, meaning two symptoms or disease travel together but one does not cause the other. One pattern that has repeatedly puzzled medical researchers is why irritable bowel syndrome seemed to follow after a viral gut infection. Now we may have some answers.
Researchers James P. White et al were not looking specifically at the effects of nerve infecting viruses on mice’s guts. They hoped to understand the effects of West Nile, Powassan, Zika and others on mice neurons. They initially ignored an unexpected finding of impaired gut motility in these infected mice. Eventually, curiosity won out and a closer look at the affected mice’s guts revealed that gut neurons had been killed off. Without these gut related nerves, the intestines did not push and basically the mice were constipated. They tested Chikungunya which did not affect mice nerve cells and saw no nerve cell death and no constipation.
As they watched the affected mice, eventually the guts appeared to recover function. However, when the mice were affected by unrelated viruses, ones which did not kill nerve cells, the dysfunction returned. Without the stress of further infection, guts functioned relatively normally. With the added stress of another infection, dysfunction quickly returned.
Sounds very similar to the long sought-after link between viral gut infections and irritable bowel syndrome beginnings. Epidemiological studies did not fully answer the question, but they led to researchers staying on the lookout for potential explanations. This story still has a lot more questions than answers between translating into human studies and delving into the mechanisms behind the dysfunction, not to mention searching for means of restoring normal function. This functional medicine MD looks forward to these answers, but in the meantime I will be considering ways to use this new knowledge for patients this week in clinic. Hopefully, I can use it to help someone live a healthier more abundant life.
James P. White, Shanshan Xiong, Nicole P. Malvin, William Khoury-Hanold, Robert O. Heuckeroth, Thaddeus S. Stappenbeck, Michael S. Diamond. Intestinal Dysmotility Syndromes following Systemic Infection by Flaviviruses. Cell, 2018; DOI: 10.1016/j.cell.2018.08.069