Studies on mice showed infections by respiratory syncytial virus (RSV) stripped immune cells of their ability to calm down inflammation in the lung's airways.
US researchers behind the study hope their findings will help develop ways of preventing asthma, the 'BBC News' reported.
Previous studies have shown a link between repeated lung infections with respiratory syncytial virus (RSV) and developing asthma later in life.
However, how the virus might lead to an increased risk of asthma has remained unknown.
Now a team of researchers at the University of Pittsburgh School of Medicine believe they have an explanation.
Their experiments on mice showed the virus impaired the ability of a specific part of the immune system, called regulatory T cells, to calm inflammation.
The tightened airway of an asthma patient and a healthy airway
Inflammation is an important part of dealing with an infection. However, for asthma patients, chemicals in air which come from ordinary things like dust mites, pets and mould can trigger an inappropriate inflammatory response.
Infection with RSV led to a "complete loss of suppressive function" of the regulatory T cells, after which the mice developed asthma-like symptoms," researchers Prof Anuradha Ray and Prof Prabir Ray said.
They think the finding could help scientists devise treatments, which prevent some people developing asthma.
"We feel that both prophylactic and therapeutic approaches can be developed," the researchers said.
The study was published in the journal 'Nature Medicine'.
