Warning about the danger of yet another bird flu virus

Scientists in the United States have identified a second H strain of bird flu that could cause a pandemic, they say the H5N1 strain of bird flu currently circulating the globe is not the only cause for concern.

A team from the Centres for Disease Control and Prevention (CDC) say the H5N1 strain of bird flu which has already killed 241 people and millions of bird life is not the only one that could trigger a pandemic.

The scientists say research in America has revealed other H strains of the flu virus which have started to evolve some of the traits needed to infect people easily.

The research, while it indicates there is no immediate indication that H7 flu is about to acquire potentially damaging mutations, demonstrates how critical global surveillance programs are and the scientific team say it is important that research includes this virus class as well as the more prominent H5N1.

The H5N1 strain has long been perceived as the most deadly strain since it appeared in Asia in 2003, but while it has a death rate of more than 60 per cent, it remains a disease of birds which is quite difficult for people to contract.

Almost all cases have involved close contact with infected birds - but it is however endemic in some parts of the world, particularly in Asia.

The H5N1 strain has yet to acquire the ability to transfer between people which is a prerequisite for a pandemic.

The H7 family of flu viruses also mainly affect birds - a deadly version of the H7N7 strain hit poultry in the Netherlands in 2003, and a less severe form, H7N2, broke out in the UK last year and in the period 2002 to 2004 several outbreaks of H7N3 and H7N2 have been reported.

Each of these outbreaks have had a minimal affect on humans with only one death and reported incidents of about 80 eye infections and a few mild respiratory infections.

An analysis of a case in 2003 in New York has shown that the H7N2 virus has the unusual capability of replicating in the respiratory tract of mammals which indicates that it could possibly be transmissible from person to person.

An animal study also revealed that this particular H7N2 strain could be passed from animal to animal which suggests that the virus could be acquiring an ability to bind to sugars found on the cells of the human windpipe which has happened before in all three of the 20th-century flu pandemics.

The scientists say the findings suggest that the H7 class of viruses have begun to adapt and recognise the receptors that are preferred by the human influenza virus and this is why continued surveillance and research into these viruses is imperative.

The research appears in the Proceedings of the National Academy of Sciences.