1.   It can be triggered by viruses, including those that cause upper respiratory infections, such as the influenza virus.

2.   Because the influenza virus mutates, the vaccine is altered each year to account for the strains expected to circulate during the flu season.

3.   But British researchers reported last year that in elderly people RSV might be as important as influenza viruses in causing serious and even fatal respiratory illness.

4.   But it has no effect on other families of viruses, including influenza virus.

5.   But unlike amantadine, they work against Type A and Type B influenza viruses and for most people they are associated with fewer adverse effects.

6.   Doctors are also being urged to perform rapid tests that cam detect infections like those caused by streptococcal bacteria and influenza virus.

7.   For example, influenza viruses attack only the lungs because only the lung cells have a particular enzyme that the influenza virus needs to replicate.

8.   For instance, the influenza virus jumps the species barrier, frequently moving from pigs to people.

9.   Further research might be conducted in ferrets or pigs, species that are known to be vulnerable to the same influenza viruses as humans, he said.

10.   In a series of meticulous experiments, researchers at the University of Wisconsin have pinpointed genetic changes that convert a chicken influenza virus into a deadly menace to humans.