(HK Edition)
Updated: 2005-11-14 05:48

The world has good reasons to take seriously the spreading cases of influenza, especially since H5N1 can be fatal, but that doesn't mean we all have to panic. Prior pandemics, such as those that occurred in 1918, 1957 and 1968, have demonstrated that when the bird-derived influenza virus enters the human body, it can adapt to become transmissible among humans themselves. It was reported, for example, in 1918 that a kitchen staff member of the US Army fell sick with flu one day, and 500 other soldiers contracted the same illness two days later. A week later, the flu spread around the US and one month later became a pandemic affecting the entire world. Forty million people died as a result.

A Chinese medical worker sprays disinfectant at a rurual poultry farm in Central China's Hubei Province after a fresh outbreak of bird flu on Saturday, November 12, 2005. [Xinhua]

The said rate of the current flu might be overstated. Scientific research indicates that typical influenza has a reproductive number of two infections per infection, compared with three in the SARS epidemic, but the flu has a faster generation time of three days, as opposed to 10 days for SARS. It means that after 30 days, one flu case will likely have multiplied into 1,024 while one SARS into 27.

As influenza viruses go, H5N1 is probably the most lethal. Scientists tell us that influenza viruses are classified according to the protein on their surfaces. The "H" represents Hemaglutinin protein which causes the virus to attach to and enter a cell where it replicates, and the "N" refers to Neuraminidase protein which allows newly replicated copies of the virus to exit and escape from a cell for further infections. At present, scientists recognize 15 types of H virus and 9 types of N virus. Each combination will form a new type of bird flu virus subject to further mutation.

Migratory birds have been accused of recently igniting H5N1 epidemics among domestic poultry throughout Southeast Asia and Central Asia, and among reared poultry and livestock in developing areas alleged to be responsible for the spread between poultry and humans. Notwithstanding that human-to-human infection of H5N1 is not proven yet, human infection cannot be ruled out. The WHO declares it will only be a matter of time as the virus evolves and mutates.

Albeit H5N1 is dangerous, the mortality ratio of about 60 deaths in 120 cases may also be misleading. Some data of patients who got H5N1 but recovered later may have not been taken into account, whereas fatal statistics are more accurately recorded. The fatality ratio should be normally several per cent of all infected cases, much less than SARS.

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