Crossing the species barrier is an important step in the development of a flu virus with pandemic potential. Previous studies have focused on the ability of highly pathogenic strains, such as H5N1 "bird flu" circulating in Asia, to spread from poultry to humans. The new study shows less pathogenic strains are also capable of jumping to humans, giving them the opportunity to swap genetic material with human strains, which could result in a more virulent virus.
Researchers in Italy studied outbreaks that occurred among poultry between 1999 and 2003, to determine the risk of avian influenza virus transmission to persons in contact with the animals. 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 investigators performed a serologic analysis of individuals exposed to infection during the outbreaks, collecting 983 blood samples from poultry farm workers in the outbreak regions. Blood was tested using three different techniques to ensure the validity of results.
The outbreaks involved two serotypes of avian influenza: one low and one highly pathogenic H7N1 and a low pathogenic H7N3 virus. Seven individuals exposed to the more recent outbreak of low pathogenic H7N3 tested seropositive for H7N3. The infected persons came from different farms in two locations and had close contact with turkeys or chickens. No serious symptoms were reported in connection with the infections.
The authors of the study, Dr. Isabella Donate