LOS ANGELES, Sept. 13 (Xinhuanet) -- Less virulent strains of avian influenza virus can spread from poultry to humans, adding to the danger of a flu pandemic, scientists reported on Tuesday.
In a paper to be published in the Oct. 1 issue of the Journal of Infectious Diseases, a research group from Italy noted that crossing the species barrier is an important step in the development of a flu virus with pandemic potential.
Thus, the seemingly not-so-harmful, less pathogenic avian influenza virus strains are also capable of causing a flu pandemic by jumping to humans and swapping genetic material with human flu viruses to produce a more virulent hybrid strain, the researchers warned.
Previous studies had only focused on the ability of highly pathogenic strains, such as the H5N1 bird flu circulating in Asia, to spread from poultry to humans.
To determine the risk of avian influenza virus transmission to persons in contact with the animals, the researchers led by Simona Puzelli studied outbreaks that occurred among poultry between 1999and 2003 in Italy.
The outbreaks occurred in northern Italy in regions where the majority of the country's commercial poultry are raised on farms. Most previous cases of human infection with avian influenza viruses have involved close contact with infected poultry, particularly ill or dying chickens.
The researchers analyzed serum samples of individuals exposed to infection during the outbreaks, collecting 983 blood samples from poultry farm workers in the outbreak regions.
The outbreaks involved two serotypes of avian influenza, one low- and one highly-pathogenic H7N1 virus, and a low-pathogenic H7N3 virus. Seven individuals exposed to the more recent outbreak of low-pathogenic H7N3 tested positive for H7N3 while showing no serious symptoms, the researchers found.
The researchers noted that their work provides the first serologic evidence of transmission of low-pathogenic strains of avian influenza virus to humans during an outbreak in poultry. In contrast, previous reports of human infection in Asia, Canada, andthe Netherlands have been associated with highly-pathogenic strains.
These findings highlight the importance of improving disease surveillance not only during outbreaks of highly-pathogenic avian flu, but also when less pathogenic strains are circulating, said the researchers, adding that very sensitive serologic techniques provide an efficient tool for preventing or controlling the spreadof avian flu to humans.
To forestall genetic exchange between human and avian strains, as in mixed infections, they noted that poultry workers should be systematically vaccinated, pointing out that such workers are identified as high-risk.
"The transmissibility of avian viruses may increase as the viruses adapt to humans," said Frederick Hayden, a professor of the University of Virginia, and Alice Croisier, an expert of the World Health Organization.
"In affected countries, public education about simple precautionary measures for food preparation, poultry handling, and avoidance of contaminated water are essential until specific prevention measures such as vaccines become available," they wrotein an editorial of the journal. Enditem
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