Research reveals ongoing evolution of bird flu in Europe
Detailed genetic studies of H5N1 bird flu samples collected in Europe, the Middle East and Africa have revealed the existence of a distinct Euro-African strain of the disease in the region and shed new light on the spread of the disease. The study, which was partly funded by the EU, is published in the journal Emerging Infectious Diseases. Researchers sequenced the entire genomes of 36 samples of H5N1 taken from birds found in Europe, the Middle East, Africa (EMA) and Vietnam. Bird flu was first detected in the EMA region in late 2005 and early 2006. The researchers found that the samples from the EMA region were closely related, despite being taken from birds found as far apart as Slovenia, Afghanistan and Sudan. The samples all fell into a distinct Euro-African lineage which is distinct from the three other major H5N1 lineages currently circulating in Asia. This EMA strain has subsequently split into three sub-lineages. 'This is the first time anyone's looked at all of the H5N1 genomes in the west,' commented the University of Maryland's Steven Salzberg, the lead author of the paper. 'Until now, the studies have been primarily on samples from the far east. Our study shows that the virus is spreading west, and that there have been three separate introductions of H5N1 in Europe, the Middle East and Africa.' 'The shared lineage of the viruses suggests a single genetic source for introduction of influenza (H5N1) into western Europe and northern and western Africa,' write the researchers, who trace back this source to either Russia or Qinghai Province in China.' Furthermore, while the three sub-lineages are now evolving independently, one virus sample taken from a Nigerian chicken turned out to have a genome which is the result of a combination of two of the EMA sub-lineages. According to the researchers, the fact that all three sub-lineages are found in the same geographic area means there are ample opportunities for such 'reassortment' events. 'Additional surveillance will be necessary to determine if this reassortant strain spreads further in the avian population and to assess its ability to infect mammals,' the researchers note. The study also revealed that the EMA strains have a mutation which is associated with virulence in mice and adaptation to mammalian hosts. 'The spread of EMA has coincided with the rapid appearance of cases in mammals - including humans in Turkey, Egypt, Iraq and Djibouti, and cats in Germany, Austria and Iraq,' the researchers warn, adding that the EMA strains of the virus appear too be as virulent as the Asian strains, with almost half of all cases in humans proving fatal. According to the researchers, the broad dispersal of the disease also suggests that human movement, and not the migration of wild birds, is primarily responsible for the rapid spread of H5N1. 'The migratory pathways of wild birds don't correspond with the movement of the genomes that we sequenced,' explained Dr Salzberg. 'Humans carry chickens between many of the countries in our study, often transporting them across great distances. That and the weak biosecurity standards in most rural areas point to human-related movement of live poultry as the source of the introduction of H5N1 in some countries.' 'These findings show how whole-genome analysis of influenza viruses is instrumental to the better understanding of the evolution and epidemiology of this infection,' the researchers conclude. 'This and related analyses, facilitated by global initiatives on sharing influenza data, will help us understand the dynamics of infection between wild and domesticated bird populations, which in turn should promote the development of control and prevention strategies.' The study brought together researchers from many countries, including Egypt, Ivory Coast, Iran and Afghanistan. 'Collaborations like this one are essential if the scientific community is going to keep track of avian flu, but most influenza researchers continue to work in isolation,' commented Dr Salzberg. 'We have to recognise that flu knows no boundaries, and we must not only collaborate widely, but also share out data freely with one another, as we have in this study.'