Viral infections may cause asthma

Asthma may be caused by viral infections in newborn babies that "cripple" the immune system and leave a child vulnerable to asthma later in life, according to a new study.

Researchers in the United States studying mice found that infection by a the respiratory syncytial virus (RSV) interfered with the ability of the immune system to reduce inflammation in the airways of the lungs.

The study confirms the findings of previous studies which had identified a link between RSV and asthma in later life.

Writing in the journal Nature Medicine, the research team from the University of Pittsburgh School of Medicine said their findings could pave the way for new ways of preventing asthma.

The delicate airways in the lungs tightened and become inflamed, producing too much sticky mucus, if they are irritated in an asthma patient.

While inflammation is a normal part of the body's response to external pathogens, the overall effect in asthmatics is to clog up the airways and make breathing difficult.

A study carried out in Sweden found that 39% of babies who were hospitalised with RSV had developed asthma by the time they reached 18, compared with just 9% of people who did not go to hospital with RSV infections.

Asthma can be triggered by chemicals in the air we breathe that are produced by ordinary things in the environment that should not normally trigger an immune response. Asthma attacks have been linked to the presence of dust mites, pet dander and mould, all of which can trigger an inappropriate inflammatory response.

According to professors Anuradha and Prabir Ray, mice infected with RSV experienced a total loss of the suppressive function in their T cells, which regulate the immune system.

The mice then went on to develop symptoms of asthma, possible because of a window in early life when the immune cells were particularly vulnerable to this crippling effect.

Asthma experts said the findings had great potential, and could help scientists devise treatments which prevent some people developing asthma.

The researchers said that their results could yield both preventive interventions and treatments for people who already have asthma.

Infants with a strong family history of asthma in particular would benefit from such treatments.

According to Malayka Rahman, of the charity Asthma UK, the research has provided "vital information" about how viruses interact with immune cells and why this might put a person at increased risk of asthma.

The findings had potential to translate into new treatments in the years to come, Rahman said.

Experts say that asthma is probably a complex of separate, overlapping syndromes, rather than a single disease.

However, little is known about the pathology behind the syndrome, and there is currently no standard way of identifying different sorts of asthma.

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