Via Nature News & Comment, Declan Butler writes: Europe's bird-flu outbreaks pose little risk to humans. Excerpt:
Three outbreaks of avian influenza virus have been reported in Europe this month. Nature explains how European countries are likely to quickly contain the outbreaks, and why the viruses poses little or no risk to people.
On 6 November, German authorities reported an outbreak of H5N8 virus at a turkey-fattening plant in Mecklenburg–Western Pomerania in the northeast of the country. Around 5,000 birds were reported to be infected and 1,880 died, in a flock of some 30,000 birds. On 16 November, Dutch authorities also reported an outbreak of the virus near Utrecht, which killed 1,000 birds in a flock of some 150,000 layer and breeding hens.
Then on 17 November, the UK Department for Environment, Food & Rural Affairs reported an outbreak of H5 avian flu in a flock of 6,000 birds at a duck-breeding farm in northern England. Further testing has revealed that there, too, the strain was H5N8.
Has H5N8 been reported in Europe before? And where did it come from?
The H5N8 virus was first detected in poultry in Ireland in 19831, and it has since occasionally been detected in the United States and Asia. The current European outbreaks, however, are of a more recent strain of H5N8 that has emerged from genetic mixing of H5 viruses in Asia2. The newer virus has caused outbreaks in poultry in southeast Asia since 2010, and in poultry farms in China, and in particular South Korea, this year.
The genetic sequence of the virus involved in the German outbreak is similar to that of the virus in the South Korean one, which suggests that the virus spread from Asia to Europe. How it did so is unclear. If it travelled through poultry trade routes — usually the main driver of the spread of avian flu — outbreaks should have been reported along the way, but this has not been the case. Such outbreaks may have gone undetected or unreported, however.
Alternatively, wild birds migrating over long distances may have carried the virus. Evidence that migration plays any major part in the spread of H5N1 and other highly pathogenic avian-flu strains to poultry farms is contentious, however (see 'H5N1: Into the Americas' and 'Doubts hang over source of bird flu spread'). Whichever way these strains reached Europe, the spread of highly pathogenic avian-flu viruses beyond Asia — where most of the outbreaks occur — is not unusual.
Does H5N8 pose any health risks to people?
A risk assessment published by the European Centre for Disease Prevention and Control (ECDC) on 13 November estimated that the risk of H5N8 infecting humans and causing illness was "extremely low". The ECDC report notes that the virus shows a marked preference for avian receptors on cells in the respiratory tract3. Still, it also has the ability to bind to receptors on human cells, and scientists have also experimentally infected ferrets — a model of human infection — with H5N8, although the animals did not develop serious illness. The virus also did not transmit efficiently between ferrets4.
The biggest threat posed by the H5N8 virus is to the egg and poultry industries. That economic risk is also minimal in Europe, where animal-health authorities will quickly stamp out such outbreaks.