"Harmless" virus may hide and cause asthma

WASHINGTON (Reuters) - A usually harmless childhood virus may hide in the lungs and come back to cause wheezing and other symptoms of asthma, U.S. researchers reported on Tuesday.

They found evidence that respiratory syncytial virus or RSV stayed in the lungs of mice and caused the overactive airway symptoms that characterize asthma.

“This research suggests that there’s a potential new mechanism for asthma related to viral infections in children that could be associated with RSV,” pediatrician Dr. Asuncion Mejias of the University of Texas Southwestern, who led the study, said in a statement.

“These findings could aid in the development of preventive and therapeutic interventions for children with recurrent wheezing due to a virus such as RSV.”

Nearly every child is infected with RSV early in life, and the virus usually clears up without serious complications in about a week. But 3 percent to 10 percent of infants with RSV infections develop severe bronchitis and must be treated in the hospital.

Doctors also thought the body quickly cleared itself of those types of viruses. But writing in the Journal of Infectious Diseases, the researchers said it may persist in some children.

They previously showed that RSV infection could raise the likelihood of chronic lung disease in mice.

For this experiment, the UTSW team infected mice with either live RSV or viruses weakened by ultraviolet light or heat.

After 42 days, the researchers found evidence of the virus in every mouse infected with live RSV, but not in the others.

“Whether RSV persists in children remains to be seen, but the fact that the virus persists in mice is amazingly powerful,” said Dr. Octavio Ramilo, a pediatrician who also worked on the study.

Also, the more virus detected in the lungs of the mice, the more likely they were to have airway hyperreactivity -- or bronchospasms -- and the worse those spasms were.

Mice treated with an antibody -- an immune system protein -- targeted to RSV ended up with less virus in the lungs and developed significantly less airway hyperreactivity and lung inflammation.

“We are currently doing a study in which we are treating kids with a new antibody that is very potent,” Mejias said. “The plan is to follow them for a year to see if aggressive treatment against the virus can prevent wheezing.”

Reporting by Maggie Fox; Editing by Peter Cooney