H1N1 generally mild, but can be severe

HONG KONG, Feb. 5 (UPI) -- H1N1 influenza causes a generally mild respiratory illness, but results in severe disease or death in vulnerable individuals, researchers in Hong Kong say.

Drs. Michael C.W. Chan and Joseph S.Malik Peiris at Queen Mary Hospital in Hong Kong compared the cell infection pattern and immune responses of pandemic H1N1 to seasonal flu as well as to highly pathogenic avian influenza strains.

The researchers found that in contrast to seasonal flu, pandemic H1N1 and highly pathogenic avian flu could infect the conjunctiva, a membrane that lines the eyelids and covers the white part of the eye, suggesting an additional route of transmission as well as differences in receptor binding profile.

However, H1N1 did not differ from seasonal flu either in replication in nose, throat, and lung cells or in induction of an inflammatory immune response.

Unlike seasonal flu, which only infects cells located in the nose and the throat, pandemic H1N1 can replicate efficiently in cells deeper in the lung, similar to the more pathogenic H5N1 "bird flu,' Chan says.

The study is published online ahead of print in the April issue of The American Journal of Pathology.