April 18, 2007

 

Study shows bird flu genome births new strains as new infections spread

 

 

An international team of researchers report the first ever large-scale "reassorting" of western genomes of the deadly avian influenza virus, H5N1, according to health journal Emerging Infectious Diseases.

 

Their research of 36 genomes of the virus collected from wild birds in Europe, the Middle East and Africa (EMA), and Vietnam confirms not only that the virus has very recently spread west from Asia, but that two of the new western strains have already independently combined to create a new strain.

 

Several samples also contained the mutation associated with the form of the "bird flu" that caused several human deaths in 2006 which strengthens the virus's ability to rapidly mutate into a pathogen that may be transmitted between humans which could result into the feared pandemic of H5N1 influenza.

 

The study also produced some evidence that strengthens the case that humans have had an impact on the movement of the flu out of Asia.

 

Steven Salzberg, the study's lead author and director of the University of Maryland Centre for Bioinformatics and Computational Biology said the H5N1 virus is spreading west and the new strains has had its introductions in Europe, Middle East and Africa.

 

The new strains confirmed the study's researchers, an unusual team of scientists from 11 countries that range from US to Iran, collaborated to share data and sequence H5N1 samples taken from birds in a widely dispersed geographic region that includes Nigeria, Sudan, Egypt, Afghanistan, Iran, Slovenia, Croatia and Italy.

 

Salzberg said strains from EMA are distinct from Vietnam and other Asian strains and that it had already divided into three separate new strains. He said one of the new strains have been the cause of several deaths in Egypt and Iraq. 

 

The research showed that the three new strains, called clades, evolved independently and in different regions from a single genetic source. Salzberg said their analysis places traced the strains have come from Russia or Quinghai Province in China.

 

The study shows that the new Euro-African lineage, which was the cause of fatal human infections in Egypt and Iraq in 2006, has been introduced at least three times into the EMA region and has split into three distinct, independently evolving lineages. Two of those sublineages have recently reassorted.

 

The broad dispersal of the different forms of the virus throughout the different countries over a relatively short period of time points to the possibility of human movement, rather than wild birds as the reason for the quick spread of the H5N1.

 

According to Salzberg, the migratory pathways of wild birds don't translate with the genomes they have sequenced. He explains: "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."

 

While the study dramatically increased the number of genomes that have been sequenced, Salzberg said they need to do more surveys as the small sample that they have taken already presented significant results.

 

Salzberg said the scientific community should keep track of avian flu and not work on isolation as bird flu knows no boundaries.

 

The flu genomes in this study were all deposited in Genbank, a public database, immediately after sequencing.

 

The study was funded by the U.S. National Institute of Allergy and Infectious Diseases, US National Library of Medicine, US Army Research Office, the Italian Ministry of Health, the European Commission for the AVIFLU and FLUAID projects, and the World Organization for Animal Health and the Food and Agricultural Organization of the United Nations.