Part two of my very boring--yet stimulating--bird flu series:

Today, I ate Taco Bell at my desk and read through the Center for Disease Control (CDC) and World Health Organization (WHO) H5N1 Avian Influenza Type A (bird flu) websites. Some interesting morsels:

WHO has developed a global influenza preparedness plan, which documents many things including the phases of a pandemic. The phases are:

Interpandemic Period
Phase 1 : No new influenza virus subtypes have been detected in humans. An influenza virus subtype that has caused human infection may be present in animals. If present in animals, the risk of human infection or disease is considered to be low.
Phase 2 : No new influenza virus subtypes have been detected in humans. However, a circulating animal influenza virus subtype poses a substantial risk of human disease.

Pandemic alert period
Phase 3 : Human infection(s) with a new subtype, but no human-to-human spread, or at most rare instances of spread to a close contact.
Phase 4 : Small cluster(s) with limited human-to-human transmission but spread is highly localized, suggesting that the virus is not well adapted to humans.
Phase 5 : Larger cluster(s) but human-to-human spread still localized, suggesting that the virus is becoming increasingly better adapted to humans but may not yet be fully transmissible (substantial pandemic risk).

Pandemic period
Phase 6 : Pandemic: increased and sustained transmission in general population.

Depending on who you ask, we're either in Phase 2 or Phase 3. There has been human infection. And of the 119 that have been infected so far, half have died. But there are no current cases of bird flu infections in humans. And there has been no--or limited--human-to-human spread.

The bird flu is currently passed from birds to humans by physical contact with the infected bird or its feces. Wild birds carry the bird flu naturally in their intestines. It will become airborne transmissible from human to human when the virus changes. And because the virus does not commonly infect humans, there is little or no immune protection in the human population.

So are there any other causes for concern? Yes. Several.
1. Domestic ducks can now excrete large quantities of highly pathogenic virus without showing signs of illness, and are now acting as a "silent" reservoir of the virus, perpetuating transmission to other birds. This adds yet another layer of complexity to control efforts and removes the warning signal for humans to avoid risbehaviorsurs.
2. When compared with H5N1 viruses from 1997 and early 2004, H5N1 viruses now circulating are more lethal to experimentally infected mice and to ferrets (a mammalian model) and survive longer in the environment.
3. H5N1 appears to have expanded its host range, infecting and killing mammalian species previously considered resistant to infection with avian influenza viruses.
4. The behavior of the virus in its natural reservoir, wild waterfowl, may be changing. The spring 2005 die-off of upwards of 6,000 migratory birds at a nature reserve in central China, caused by highly pathogenic H5N1, was highly unusual and probably unprecedented. In the past, only two large die-offs in migratory birds, caused by highly pathogenic viruses, are known to have occurred: in South Africa in 1961 (H5N3) and in Hong Kong in the winter of 2002-2003 (H5N1).