Understanding Pneumonia Caused by Avian Flu

The authors of a new "Brevium" article in the 24 March 2006 issue of Science have identified cell types in the human lung to which a currently circulating avian influenza virus predominantly attaches.

The new study may help to explain why the H5N1 virus has been relatively unsuccessful in passing from humans to other humans thus far: the virus appears to attach and replicate deep within the human respiratory tract, which decreases the risk of spreading the virus to others from actions such as coughing and sneezing.

In human lung tissue, the H5N1 virus attached abundantly to cells lining the alveoli called type II pneumocytes, scavenging cells within the lumen of the alveoli called alveolar macrophages, and cells that line the wall of the bronchioli, the authors say. These findings contrast the previously held notion that avian influenza viruses have little affinity for cells of the human respiratory tract, said Science author Thijs Kuiken.

Avian influenza attachment became progressively less dense towards the windpipe or trachea which is higher up in the respiratory tract, according to the authors who say their findings fit with the limited data from human autopsies. The researchers also compared the pattern of H5N1 virus attachment within the respiratory tracts of humans, mice, ferrets, macaques and domestic cats.

The pattern of H5N1 virus attachment in the lower respiratory tract of cats, and to a lesser extent, ferrets most closely resembles the pattern in human tissue, suggesting that these animals may serve as suitable models for H5N1 viral pneumonia in humans, the authors say.

Science reported last week on a new potential pathway for Avian flu transmission to humans. For a summary, click here.

Daniel B. Kane

22 March 2006