Viral infections could raise children's asthma risk
16 May 2007

Children who catch lower respiratory viral infections, such as the common cold, during their first year of life and are also prone to allergies are at greater risk of developing asthma, according to new research.

Scientists at Imperial College London and the University of Western Australia in Perth have determined that children under the age of two who experience this combination of allergies and viral infections are much more likely to develop asthma later in childhood.

They believe that a viral infection may make their immune systems view allergens as a threat if both are encountered at the same time. This leaves children highly sensitised to the particular allergen, which can lead to asthma attacks when their immune system reacts to any subsequent exposure.

The researchers studied almost 200 children for five years, recording the viruses they were infected with during their first year of life and when they developed allergies.

They found that those children who had a lower respiratory viral infection during their first year of life and developed sensitivity to an allergen before they were two were three to four times more likely to suffer from asthma at the age of five.

Prof Johnston, one of the researchers from Imperial College London said: ‘If you are exposed to an allergen early in life, the body usually becomes tolerant of it. There is also pretty clear evidence that infections in general early in life are likely to protect you from developing allergies.

'What we have found is that there is a strong relationship between children who suffer lower respiratory illness early in life and the risk of them developing asthma later.

'It may be a matter of bad timing, so that if a child is exposed to an allergen at the same time as a lower respiratory virus infection, then the child might become sensitised to that allergen instead of being tolerant of it.

'We clearly need to understand the role of viral infections early in life very much better to try to understand how some infections, perhaps at certain times or sites may be harmful, while infections in general seem to be a good thing in terms of reducing the risk of developing asthma and allergies later’

Dr Victoria King, Asthma UK’s Research Development Manager, said: 'Asthma is the most common long-term condition for children in the UK affecting 1 in 10. This research suggests that severe viral infections combined with sensitivity to allergies during the first year of a child’s life may lead to the development of asthma later in childhood.

'Childhood is an important time when the immune system is developing; this research gives us a further insight into this developmental window at a very early age and its association with asthma. Asthma UK welcomes further research into early life risk factors and the development of asthma.'