Wednesday, May 10, 2006

Transmission through the gut?

It is usual to think of influenza as a respiratory disease because that's how it appears in humans. But in birds it is a disease of the intestinal tract, and the current H5N1 subtype as well as the 1918 variety invaded organ systems outside the lung, most obviously the nervous system. The notion that the disease couldn't be transmitted via food is based partially on the respiratory notion and partially on the mistaken impression that the acid environment of the stomach would kill any virus. We discussed this in an earlier post and warned that there was still much to learn about other routes of transmission. Now, Menno de Jong, head of the virology department at the Oxford University Clinical Research Unit in Ho Chi Minh City is cautioning that the intestinal tract may indeed be a portal of infectious entry.
Bird flu may be capable of invading people through the gut, not just the respiratory system, and diarrhea is sometimes the first symptom, said virologist Menno de Jong, whose team observed 18 cases in Vietnam.
Particles of the lethal H5N1 virus contained in the meat and blood of infected poultry may have been ingested by some patients, possibly causing their infection, said De Jong . . . .

"In a number of patients the only exposure risk has been drinking raw duck blood,'' De Jong said in a phone interview yesterday. "That could imply that the gastrointestinal tract is also a route of transmission or a route of first infection, and there are experiments in animals'' that suggest this. (Bloomberg)
We will say again what we have said repeatedly. This virus has the ability to surprise. It is now not beyond imagining it capable of either foodborne or waterborne spread, although neither has been demonstrated in human influenza transmission to date. Waterborne spread is a known route of transmission in wild birds, however, so the virus is able to remain replicable in these media. The frequency of diarrhea as a presenting symptom of H5N1 infection is a red flag. The fact that one can isolate virus from rectal swabs in some human cases is a red flag. The fact that the virus can invade other organ systems besides the lung is a red flag. Lots of red flags.

But not the time for a white flag. Much can be done and there is much to do. Calmly, patiently and with eyes open to all possibilities.