| Abstract: | Influenza A-viruses are divided into two distinct groups based on their ability to cause disease in birds: low pathogenic and highly pathogenic avian influenza (LPAI and HPAI). Only viruses of the H5 and H7 subtype have been shown to cause HPAI. Migratory birds are the reservoir of influenza A-viruses and are the source of LPAI viruses that may mutate into HPAI viruses in domestic poultry, causing severe disease outbreaks with high mortality in these animals. Since 1997, it has become clear that avian influenza viruses may infect humans: in Hong Kong 18 people became infected with the HPAI H5N1 virus and 6 of them died. In 2003, a massive outbreak of HPAI amongst poultry in The Netherlands, caused by a H7N7 virus, resulted in 89 clinical cases among farmers and poultry workers, one of which was fatal. The ancestors of this H7N7 virus had been found in migratory ducks prior to the outbreak. The virus had probably spilled over as a LPAI H7N7 virus to free-range chickens, in which it mutated to an HPAI virus.In the past three years, outbreaks of HPAI in domestic poultry in Asia, caused by HPAI H5N1 viruses were associated with about 200 severe human infections, more than half of which were fatal. From Asia, HPAI H5N1 virus infections spread to the Middle East, Europe and Africa; affecting domestic poultry, wild birds and a number of mammalian species. Also from Turkey and the Middle East, human cases — some with fatal outcome — were reported. The pattern of spread largely coincided with the flyways of migratory birds.The respective zoonotic events constitute a severe warning for the looming threat of an influenza pandemic. Avian influenza A-viruses may adapt to efficient human-tohuman transmission, either directly by mutation or by reassortment with mammalian influenza A-viruses. Since little or no immunity is likely to exist against such a virus in the human population, this may result in a pandemic outbreak of influenza. Although several countries are currently preparing for such an event by developing "andemic preparedness plans" according to WHO recommendations, the world at large is not sufficiently prepared for such a catastrophe. Better collaboration and coordination between all the stakeholders is urgently needed to establish early warning systems and effective global pandemic preparedness plans. One way forward would be the establishment of a global task force for influenza.Note from Publisher: This article contains the abstract only. |
