Fifteen years after avian influenza killed six people in Hong Kong Special Administrative Region of China in 1997, poultry selling practices have changed radically because the government took the step that year of ordering a slaughter of all poultry in the city, effectively halting the disease in its tracks.
Despite sporadic outbreaks among poultry, there have been no human cases originating in the city and its poultry industry has undergone a transformation.
Although live poultry is still sold in the city’s fresh produce, or wet, markets, the government revoked licenses from three quarters of the poultry traders in 2008, dramatically reducing the number of locations where live poultry is sold.
There used to be compulsory monthly rest days for poultry stalls; since 2008 this has been extended to a ban on keeping live birds overnight in retail markets so all poultry must be slaughtered at the end of each working day. There have also been periodic bans on poultry selling whenever birds infected with the virus have been found at or near markets or the city’s 30 poultry farms.
Professors Malik Peiris, Tam Wah-Ching and their colleagues at Hong Kong University (HKU) Pasteur Research Centre, are currently documenting the impact of these interventions to control H5N1 avian influenza among poultry. “We have found that they dramatically reduce the amplification of avian flu viruses in wet markets, thus reducing risk to humans.
"Unfortunately, Hong Kong SAR is one of only a few places that is doing any of these things. From the point of view of the safety of Hong Kong SAR, the measures are effective but H5N1 is certainly not under control in many parts of Asia. That is the concern, especially now that we know it can potentially acquire human-to-human transmissibility.”
It is this potential for transmissibility and the threat of a possible pandemic that is keeping epidemiologists occupied. Two groups in the Netherlands and the United States of America have demonstrated that the virus can be altered to enable transmissibility in ferrets, and research on vaccines that can neutralize all influenza A viruses is also ongoing.
According to the World Health Organization (WHO), people in countries experiencing outbreaks of H5N1 in poultry will likely continue to be exposed to the virus through contact with infected poultry or contaminated environments; and therefore sporadic human cases will occur as long as the virus continues to circulate in poultry, especially in household poultry.
Worldwide, as of 6 July this year, there had been 607 reported human cases and 358 deaths in 15 countries, according to WHO. “Although this case–fatality estimate may be skewed by a bias in detecting more severe cases, there is no doubt that H5N1 is the nastiest of all the flu viruses around currently. The 2009 H1N1 pandemic virus itself is relatively benign and has not changed much antigenically,” says Peiris.
Egypt, Indonesia and Viet Nam account for 80% of all cases since 2003 and 78% of all avian influenza deaths. WHO is working with these and other countries that are most affected to better prevent, detect and deal with human cases of avian influenza.
In the process, this is leading to far wider benefits – health system improvements that leave countries better prepared for other threats to public health.