Viruses such as West Nile and Zika that target the nervous system in the brain and spinal cord also can kill neurons in the guts of mice, disrupting bowel movement and causing intestinal blockages, U.S. researchers have found.
Other viruses that infect neurons also may cause the same symptoms, the researchers at Washington University School of Medicine in St. Louis said.
The researchers at the university who study mice infected with West Nile virus noticed that the intestines of some of the infected mice were packed with waste higher up and empty farther down, as if they had a blockage.
"We actually noticed this long ago, but we ignored it because it wasn't the focus of our research at the time," said West Nile expert Michael S. Diamond, a professor of Medicine and the study's co-senior author.
This time, the researchers dug in, and found that not only West Nile virus but its cousins Zika, Powassan and Kunjin viruses caused the intestines to expand and slowed down transit through the gut.
Further investigation showed that West Nile virus, when injected into a mouse's foot, travels through the bloodstream and infects neurons in the intestinal wall. These neurons coordinate muscle contractions to move waste smoothly through the gut. Once infected, the neurons attract the attention of immune cells, which attack the viruses and kill the neurons in the process.
"Any virus that has a propensity to target neurons could cause this kind of damage," said Diamond.
Though West Nile and related viruses are not very common in the United States, there are many other viruses that are more widespread, such as enteroviruses and herpesviruses, that also may be able to target specific neurons in the wall of the intestine and injure them."
If it is the case, such widespread viruses may provide a new target in the prevention or treatment of painful digestive issues.
"Many of the viruses that might target the gut nervous system cause mild, self-limiting infections, and there's never been reason to develop a vaccine for them," Diamond said. "But if you knew that some particular viruses were causing this serious and common problem, you might be more apt to try to develop a vaccine."
The infected mice's digestive tracts gradually recovered over an eight-week time span. But when the researchers challenged the mice with an unrelated virus or an immune stimulant, the bowel problems promptly returned.
This pattern echoed the one seen in people, who cycle through bouts of gastrointestinal distress and recovery.
The findings were published Oct. 4 in the journal Cell.
