Excerpt from WHO’s latest risk assessment for the H5N1 bird flu virus:
Implications for human health
The poultry outbreaks in Russia and Kazakhstan are caused by a virus that has repeatedly demonstrated its ability, in outbreaks in Hong Kong in 1997, in Hong Kong in 2003, and in south-east Asia since early 2004, to cross the species barrier to infect humans, causing severe disease with high fatality. A similar risk of human cases exists in areas newly affected with H5N1 disease in poultry.
Experience in south-east Asia indicates that human cases of infection are rare, and that the virus does not transmit easily from poultry to humans. To date, the majority of human cases have occurred in rural areas. Most, but not all, human cases have been linked to direct exposure to dead or diseased poultry, notably during slaughtering, defeathering, and food preparation. No cases have been confirmed in poultry workers or cullers. No cases have been linked to the consumption of properly cooked poultry meat
Factors relating to poultry densities and farming systems seen in different countries may also influence the risk that human cases will occur. During a 2003 outbreak of highly pathogenic avian influenza, caused by the H7N7 strain, in the Netherlands, more than 80 cases of conjunctivitis were detected in poultry workers, cullers, and their close contacts, and one veterinarian died. That event, which was contained following the destruction of around 30 million poultry, underscores the need for newly affected countries to follow FAO/OIE/WHO recommended precautions when undertaking control measures in affected farms.
Pandemic risk assessment
The possible spread of H5N1 avian influenza to poultry in additional countries cannot be ruled out. WHO recommends heightened surveillance for outbreaks in poultry and die-offs in migratory birds, and rapid
introduction of containment measures, as recommended by FAO and OIE. Heightened vigilance for cases of respiratory disease in persons with a history of exposure to infected poultry is also recommended in countries with known poultry outbreaks. The provision of clinical specimens and viruses, from humans and animals, to WHO and OIE/FAO reference laboratories allows studies that contribute to the assessment of pandemic risk and helps ensure that work towards vaccine development stays on course.
The expanding geographical presence of the virus is of concern, as it creates further opportunities for human exposure. Each additional human case increases opportunities for the virus to improve its transmissibility, through either adaptive mutation or reassortment. The emergence of an H5N1
strain that is readily transmitted among humans would mark the start of a pandemic.