However, the link between RSV and later onset of asthma is also seen in milder cases of the infection. The American COAST study was designed to examine the effect of childhood respiratory infections on the risk of developing asthma. Researchers followed 259 newborns prospectively for 1, 3, and 6 years. To qualify, at least one parent was required to have respiratory allergies (defined as one or more positive aeroallergen skin tests) or a history of physician-diagnosed asthma. Regular samples taken during infectious episodes identified a virus in 90% of cases.
“We now know that RSV is not the only pathogen responsible for bronchiolitis. RV is often found, now that it can routinely be detected by PCR tests,” said Dr. Taillé. In the COAST study, the onset of wheezing during an RSV or RV infection in children aged 0-3 years was associated with an increased risk of asthma at 6 years of age. Globally, 28% of children infected by either virus were deemed to have asthma at 6 years of age. “There is clearly a link between having had a respiratory virus like RV or RSV and getting asthma symptoms at 6 years of age,” said Dr. Taillé. “What’s more, the effect of RV is not changed in this study by allergic sensitization.”
Many articles have been published on this topic. The results of cohort studies, from Japan to Finland and the United States, Italy, and Australia, are consistent with each other. Persons who have contracted RV or RSV are more likely to suffer from recurrent wheezing or asthma, especially if the infection is contracted in infancy or if it is severe. “Some studies even suggest that viral-induced asthma is more severe,” said Dr. Taillé. “For example, a Scottish study ... showed that children with a previous history of RSV infection had more hospital admissions and required more medication than asthmatics with no history of an RSV infection, suggesting the link between a previous history of RSV infection and the development of a more severe form of asthma.”
Reaching adulthood
Few longitudinal cohorts explore this issue in adulthood. A relatively old study reported an increased rate of asthma among adults who had required hospital admission for bronchiolitis in early childhood, as well as the effect on respiratory function. A 2023 study of the effects of respiratory illnesses in childhood reported similar findings. The authors evaluated lung structure and function via CT scans of 39 patients aged 26 years and concluded that participants who had been infected with RSV in childhood presented with increased air trapping, which is suggestive of airway abnormalities, possibly linked to a direct effect of viruses on lung development.
Mechanisms of action
“The real question is understanding if it’s the virus itself that causes asthma, or if the virus is simply uncovering underlying asthma in predisposed children,” said Dr. Taillé. From 30% to 40% of children who have had RSV will go on to develop wheezing or asthma in childhood. This observation suggests that there are factors favoring the development of asthma after infection with RSV. It has been shown that there is a genetic predisposition for RV. The roles of cigarette smoke, air pollution, environmental exposures to allergens, rapid urbanization, low vitamin D levels, low maternal omega-3 long-chain polyunsaturated fatty acid levels, maternal stress, and depression have also been highlighted.
It would seem that RSV and RV are a bit different. RV is thought to be associated with the development of asthma and wheezing, especially in people with a preexisting atopy or a reduced interferon immune response, while RSV, which occurs at a younger age and among the most vulnerable populations, seems to act independently of a person’s predisposition to allergies. RV stands out from other viral factors, owing to its tendency to create a Th2-biased inflammatory environment and its association with specific risk genes in people predisposed to asthma development (CDHR3).
Dr. Taillé has disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.