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•The H5N1 influenza strain continues to evolve (Li 2004), and some clones have broader binding properties which may reflect a certain degree of adaptation in human hosts (Le 2005). H5N1 has expanded its host range not only in avian species (Perkins 2002), but also in mammals, naturally infecting humans, tigers, leopards, domestic cats and a stone marten (Keawcharoen 2004, Thanawongnuwech 2005, Amonsin 2006).

•The H5N1 virus has increasingly pathogenic features in mice and ferrets (Zitzow 2002, Govorkova 2004).

•Ducks have recently been shown to be able to excrete highly pathogenic H5N1 strains for up to 17 days (Hulse Post 2005).

•In Central China, more than 6,000 migratory birds died at the Qinghai Lake nature reserve in central China in late April 2005. Before that event, it was highly unusual for wild birds to die from highly pathogenic avian influenza viruses (WHO 20050818).

•Viruses from very different locations (Qinghai Lake, Nigeria, Iraq, Turkey, Russia, Kazakhstan, and Mongolia) all showed a distinctive mutation which is associated with greater lethality in birds and mice. Such genetic stability over many months is unusual and raises the possibility that the virus – in its highly pathogenic form – has now adapted to at least some species of migratory waterfowl and is co-existing with these birds in evolutionary equilibrium, causing no apparent harm, and travelling with these birds along their migratory routes (WHO 20060220).

•In an unpublished study carried out in 2005 in central Thailand, 160 out of 629 dogs had antibodies to H5N1 (Butler 2006).

•Domestic cats are usually considered resistant to influenza. However, when fed with H5N1 virus-infected chickens, cats developed severe disease and transmitted the virus to other cats (Kuiken 2004). Cats may excrete virus not only via the respiratory tract but also via the digestive tract (Rimmelzwaan 2006), suggesting that spread by potentially novel routes within and between mammalian hosts might be possible. In February 2006, H5N1 influenza was found in a domestic cat (WHO 20060228) and in a stone marten (WHO 20060309) on the German island of Ruegen where more than 100 wild birds had died in the previous two weeks.

•Human H5N1 isolates from 2003 and 2004 exhibited a substantially greater level of virulence in ferrets than other H5N1 viruses isolated from humans since 1997 (Maines 2005).

Individual Management

Try not to get the bugs, and if you get them, try to treat them. In influenza management, this one-line medical wisdom theoretically translates as: 1) three prophylaxis defence lines (exposure prophylaxis, vaccination, prophylactic use of antiviral drugs); and 2) one treatment defence line (antiviral drugs). Due to the very nature of influenza infection – infected individuals may be infectious for as long as 24– 48 hours before the onset of symptoms – exposure prophylaxis is virtually impossible during an ongoing epidemic or pandemic, especially in our highly