MARSEILLE, France — It is well known that viral infections, especially respiratory syncytial virus (RSV) and rhinovirus (RV), exacerbate symptoms of asthma. But could they also play a part in triggering the onset of asthma?
The link between RSV and RV infections in early childhood and the development of asthma symptoms is well established, said Camille Taillé, MD, PhD, of the department of respiratory medicine and the rare diseases center of excellence at Bichat Hospital in Paris. But getting asthma is probably not just a matter of having a viral infection at a young age or of having a severe form of it. Gene polymorphisms, immune system disorders, and preexisting atopy are also associated with the risk of asthma. This was the focus of the 27th French-language respiratory medicine conference, held in Marseille, France.
RV and RSV
Persons with asthma are vulnerable to certain viral respiratory infections, in particular the flu and RV, which can exacerbate asthma symptoms. Inhaled corticosteroids have an overall protective effect against viral-induced exacerbations. For worsening asthma symptoms during an epidemic or pandemic, there is no contraindication to inhaled or oral corticosteroids.
Young children from the time of birth to 4 years of age are particularly susceptible to viral respiratory infections. According to data from France’s clinical surveillance network, Sentinelles, from the period covering winter 2021 to 2022, the rate of incidence per 100,000 inhabitants was systematically greater for the 0 to 4-year age range than for older age ranges.
Of the most common viruses that infect young children, RV, the virus that causes the common cold, is a nonenveloped RNA virus from the enterovirus family. There are 160 types, which are classified into three strains (A, B, and C). Of those strains, A and C confer the most severe infections. The virus is highly variable, which makes developing a vaccine challenging. The virus circulates year round, usually peaking in the fall and at the end of spring. RSV is an RNA virus that is classed as a respiratory virus. It comprises two serotypes: type A and B. Almost all children will have been infected with RSV by the time they are 2 years old. Epidemics occur each year during winter or in early spring in temperate climates. Vaccines are currently being developed and will soon be marketed. A monoclonal antibody (palivizumab), which targets fusion proteins of the virus, is available as prophylactic treatment for at-risk children.
During an RSV infection, the severe inflammation of the bronchial and alveolar wall causes acute respiratory distress. “But not all infants will develop severe forms of bronchiolitis,” said Taillé. “The risk factors for the severe form of the illness are well known: being under 6 months of age, prematurity, comorbidities (neurovascular, cardiovascular, respiratory, etc), history of a stay in a neonatal intensive care unit at birth, living in low socioeconomic status towns, and exposure to smoking.”
The issue of whether or not viral diseases cause asthma has been the subject of intense debate. The studies are starting to stack up, however. They seem to show that RSV or RV infections are associated with the risk of subsequent asthma development. “For example, in a study published in 2022,” said Taillé, “in children admitted with an RSV infection, 60% of those who had been admitted to neonatal intensive care presented with symptoms of asthma between 3 and 6 years of age, compared with 18% of those who had had a milder case of RSV (admitted to nonintensive care settings). A serious RSV infection is a risk factor for later development of asthma.”
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 Taillé. In the COAST study, the onset of wheezing during an RSV or RV infection in children aged 0 to 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 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 Taillé. “For example, a Scottish study published in 2020 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.”
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 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).
Taillé has disclosed no relevant financial relationships.
This article was translated from the Medscape French Edition.