(LifeWire) - Viral-induced asthma is what can happen when viruses cause asthma symptoms. When it comes to asthma, sometimes a simple common cold can be anything but simple. Viruses, such as those that can cause a cold or the flu, can lead to the development or worsening of asthma symptoms. There are two ways viruses can trigger asthma symptoms.
The second type of viral-induced asthma affects children and adults who already have persistent asthma; a viral illness worsens their asthma symptoms. It is estimated that at least 40% of asthma exacerbations in adults are caused by a viral illness.
Frequency and Common Causes
Several viruses can be blamed for triggering viral-induced asthma. Rhinovirus causes the common cold, and influenza A causes the flu. These are the viruses most frequently found to cause bronchospasm (narrowing of the airways) and asthma.
In a study of people with asthma who were admitted to a hospital in England over the course of 1 year, 37% had evidence of a viral infection. Of these, rhinovirus and influenza A were found to be responsible for 31% and 45% of the worsening of their conditions, respectively. It has also been shown that 80% of children with episodes of wheezing have viral infections, the majority of which belong to the family of rhinoviruses.
Respiratory syncytial virus (RSV) is a virus that causes respiratory infections in adults and children. RSV can cause wheezing, particularly in children under 2 years of age, which can lead to hospitalization and even death in rare cases. This increase in airway sensitivity sometimes lingers long after the infection has been cleared. In a study that followed 1,300 children from birth, children with severe RSV infection were more likely to have asthma symptoms until 6 years of age. There seems to be a correlation between severity of infection, history of allergies in the child or parent, and the chance of having airway sensitivity that mimics asthma.
In adults, RSV can also cause wheezing and induce asthma symptoms in those who already have asthma. It can also cause asthma-like symptoms in people with no history of asthma. In a study of daycare workers without asthma who contracted RSV, researchers found that the workers had increased problems with their airways 8 weeks after the initial RSV infection. Their airway functioning returned to normal 4 months post-infection.
Because these types of viral infections are more common during certain times of the year, viral-induced asthma cases tend to wax and wane with the seasons. Rhinovirus has a peak season in late fall, and influenza A peaks in late winter. RSV is most common in the winter months, with a peak season of January to February in the northern hemisphere.
Why Viruses Cause Asthma
When faced with a viral infection, the body triggers an inflammatory response to attack and defend. In upper respiratory infections, such as those that accompany a cold or flu, this response can cause swelling and increased sensitivity of airway cells, as well as excessive mucus production. It is unclear whether viruses attack the lower airway directly, causing asthma symptoms, or whether inflammatory substances produced by infected cells in the upper airway then affect the lower airway.
People with asthma are not more susceptible to viral infections than others, but they do suffer more from the lower airway effects of these infections.
Diagnosis of Viral-Induced Asthma
Many people with persistent asthma can sense when their symptoms are worsening. However, it is a good idea for people with asthma to have a peak flow meter – a small device that one blows into to measure how well the lungs are functioning. It is possible to have a significant decrease in peak flow numbers (less than 80% of normal) without having corresponding symptoms. Anyone who notices a significant decrease in peak flow numbers, as compared to the usual personal levels recorded on a daily basis, should call their doctor for advice about increasing asthma medications or seeking medical attention.
A doctor should be able to diagnose viral-induced asthma in those who do not have a history of asthma by listening to the lungs. Many doctors have peak flow meters in their office, which can be used to diagnose airway obstruction. Even for someone who has never used a peak flow meter, and therefore has no sense of what a usual reading for them might be, the doctor can compare the patient's numbers to what would be predicted for someone of the same sex, age and size.
At present, there are no effective medications to treat these common viruses and prevent the asthma attacks they may provoke. The best treatment is prevention. Anyone with chronic asthma should have a flu shot every year. Frequent hand washing and limited contact with people who have upper respiratory symptoms are two good ways to help limit exposure to cold and flu viruses.
Treatment for a viral-induced asthma attack may include bronchodilators (medicines that open up the airways) for mild symptoms and increased steroids for more severe or prolonged attacks.
Steroid inhalers have been shown to be effective for treating non-asthmatic adults who have asthma-like symptoms after a viral infection. However, in the absence of any history of asthma, these symptoms generally go away in 8 weeks or less. For severe viral-induced bronchospasm, oral steroids may sometimes be necessary, even in people without a history of asthma.
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