Does a virus cause some kids' asthma?

For some children with asthma, no amount of medication seems to relieve their wheezing. New research now suggests that certain children with hard-to-treat asthma may suffer from a smoldering viral infection of the lungs.

Asthma specialists have always known that some children develop the disorder after suffering an acute bronchial infection with a bug called adenovirus. Scientific dogma holds that the body's immune system clears this virus, but an infection can leave the lungs vulnerable to a chronic condition in which pollutants in the air and other allergens trigger breathlessness.

Vasilija Matek of the University Medical Center in Ljubljana, Slovenia, and her colleagues wondered if such children continue to wheeze because they never really got rid of a lung infection. To test that hypothesis, they recruited 34 children who had recovered from such an acute infection and had then been diagnosed with asthma. All 34 had failed to breathe more easily with conventional treatments, such as steroid drugs and bronchodilator medication.

The team began its study by inserting a slender tube into each recruit's trachea and collecting fluid samples from their lungs. The researchers discovered a protein made by the adenovirus in samples from 31 of the 34 children. When the researchers tested 20 children who did not suffer from asthma, they found no sign of this viral protein, Such evidence is suggestive but does not prove that the virus is actively replicating in the lungs, comments Hugh O'Brodovich, a lung specialist at the Hospital for Sick Children in Toronto.

Next, the team took lung-fluid samples from 6 of the 31 children and successfully grew cultures of adenovirus from them. "I think it's a very provocative finding," O'Brodovich says. That evidence indicates that the virus is actively replicating in the lungs of these children, he adds.

The Slovenian investigators describe their findings in the July American Journal of Respiratory and Critical Care Medicine, a journal published by the American Lung Association. The results suggest that some kids fail to quash an adenovirus infection, continuing instead with a low-grade infection that leads to chronic breathing problems. Still, these findings have yet to be confirmed, O'Brodovich says, noting that this is the first study to implicate adenovirus directly in the development of asthma.

The new research hints that antiviral therapy might benefit certain kids with intractable asthma, adds Matek. She hopes her findings will spur drug developers and clinical researchers to take a hard look at the impact of antivirals on such cases.

Does a viral infection underlie other cases of asthma, including some in the adult population? Matek suspects so, but she says further study must answer that question.

There's evidence that adenovirus also plays a part in a different respiratory ailment. James C. Hogg of St. Paul's Hospital in Vancouver, British Columbia, and his coworkers have found previously that some smokers who develop chronic obstructive lung disease show evidence of adenovirus infection.

Hogg, who wrote an editorial to accompany the Solvenian report, also points out that the new results raise a red flag for the emerging field of gene therapy Genetic researchers have employed a crippled adenovirus to carry a therapeutic gene into the pulmonary cells of cystic fibrosis patients. Matek and her team point out that some people may have a latent adenovirus infection. Hogg worries that the crippled virus may combine with the virus already in the lungs and start to spread.