The Coming Influenza Pandemic?

June 20 Flu Update

n addition to the new outbreaks in Vietnam, there have been two significant outbreaks in western China. The first outbreak was discovered in early May at Qinghai Lake Nature Reserve. Initially the deaths were limited to 180 bar headed geese, but quick rose to over 1000 dead birds representing at least 5 species of migratory birds. This outbreak was unusual in size and the fact that the H5N1 confirmed infection was lethal in geese. The outbreak in Qingahi was followed by an outbreak of domestic geese in Tacheng near the Kasakhstan border in Xinjiang, China. This H5N1 confirmed outbreak again involved lethal infections in geese.

The two outbreaks in western China were accompanied by third party reports on infections in humans. In Qinghai there were reports of deaths of 6 tourists and 121 residents in 18 communities. The reports of human cases have been denied by China, but new fever clinics were established. Another third party report described a pneumonia outbreak involving patients and health care workers in Tacheng. China again denied human cases. WHO requested permission to visit Qinghai, but there have been no reports of that request being granted.

The large number of reported human cases in Qinghai and the isolation of health care workers in Tacheng would signal phase 6, if confirmed. It is likely that the H5N1 would be carried to Kasakhstan and Russia by the migrating birds, although there have not been reports of H5N1 in the neighboring countries.

Thus, at this time it looks like H5N1 is moving from phase 5 to phase 6 in northern Vietnam, and may be doing the same in western China, if reports of human fatalities are accurate.

Of particular interest was evidence that the virus was present and replicating in the intestinal tract, although evidence of viral proteins weren't detected there. In addition, the pathologic damage was more or less confined to the extremities of the respiratory tree (the Wiki will also explain this). In other influenza infections (like the common H1 and H3 infections) there is evident damage to the upper respiratory tract, giving rise to the symptoms of running nose and hacking cough we associate with the disease. In this case it was just the areas where gas exchange takes place that were infected (the type II pneumocytes), with fluid in the spaces between the gas exchange sacs (interstitial pneumonia). There was also sign of a secondary fungal infection of the lungs, possibly a terminal event. While there was evidence of replicating virus in the intestines, the tissues looked normal. In keeping with other findings, there were increased levels of certain cytokines (chemical signalling substances induced by infection). While only suggestive, this is consistent with a role for a dysregulated defense reaction playing a part in making the infection more severe.

The presence of the virus in the intestinal tract raises the question of whether stool is infective in these patients, an important point for transmission. The localization of the virus to the lower respiratory tract also suggests that the usual nose and throat specimen swabs may be less reliable for H5 infection than for other influenza viral subtypes.

posted by Orange @ 10:38 PM