Viruses that target the brain can also lead to permanent digestive problems, a new study has warned.
Researchers from the Washington University School of Medicine in St Louis, Missouri, say their findings could explain why people report abdominal pain as a common symptom of these viruses.
In a study conducted on mice infected with West Nile and Zika viruses, immune cells killed infected neurons in the gut, which contract so that waste flows properly through the digestive tract.
This led to disrupted bowel movements and intestinal blockages that, even after they cleared, flared up again after an unrelated illness or stress.
The team says it hopes that other scientists are more apt to try to develop a vaccine to prevent this condition.
A new study from the Washington University School of Medicine in St Louis, Missouri, has found that viruses that attack your brain infect neurons in the intestinal walls, which are then killed by immune cells (file image)
First author Dr James White, a postdoctoral researcher at Washington Univeristy, has long studied mice infected with West Nile virus, a disease spread through the bites of mosquitoes that become infected after feeding on infected birds.
He noticed that some of the intestines of the infected mice were packed with waste higher up and empty farther down, implying there was some kind of blockage.
Dr White and his colleagues discovered that the phenomenon didn’t just apply to West Nile virus but similar viruses that also attack the nervous system: Zika, Powassan and Kunjin viruses
All these strains caused the intestines to expand and slowed down how quickly waste flowed through the gut.
To confirm their theory, they also examined mice infected with chikungunya virus, which is transmitted by mosquitoes but does not target the nervous system, and found that these mice did not have bowel dysfunction.
Further research showed that when the West Nile virus was injected into a mouse’s foot, it entered the bloodstream and infected neurons within the intestinal walls.
These neurons send signals to muscles that contract so that excrement can properly flow through the intestines.
However, after they become infected, immune cells attack the virus – but end up also destroying the neurons.
‘Any virus that has a propensity to target neurons could cause this kind of damage,’ said co-senior author Dr Michael Diamond, a professor of molecular microbiology and of pathology and immunology at Washington University.
‘West Nile and related viruses are not very common in the US. But 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.’
Dr Diamond added that the disrupted bowel condition, known as chronic gastrointestinal motility, can be managed but not prevented or cured.
After eight weeks, the digestive tracts of the infected mice mostly recovered but, when the mice were infected with an unrelated virus, their bowel problems returned.
While gut flare-ups can also be triggered by stress or illnesses, they can occur without an obvious cause.
‘It’s amazing that the nervous system of the gut is able to recover and re-establish near normal motility, even after taking a pretty big hit and losing a lot of cells,’ said co-senior author Dr Thaddeus Stappenbeck, a professor of developmental biology at Washington University.
‘But then, it’s really just barely functioning normally, and when you add any stress, it malfunctions again.’
The authors said for future research, they would like to study the effect that damage to the gut neurons has on the microbiome, the collection of bacteria lives in the body.