Submitted to: Emerging Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2003
Publication Date: 4/1/2004
Citation: Suarez, D.L., Senne, D.A., Banks, J., Brown, I.H., Essen, S.C., Lee, C.W., Manvell, R.J., Mathieu-Benson, C., Marreno, V., Pedersen, J., Panigrahy, B., Rojas, H., Spackman, E., Alexander, D.J. Recombination Resulting In Virulence Shift In Avian Influenza Outbreak, Chile. Emerging Infectious Diseases. Vol 10, No.4. Interpretive Summary: Avian influenza is a viral disease of birds that can occur in a mild form, low pathogenic avian influenza, or a severe form, highly pathogenic avian influenza. The highly pathogenic form of the virus causes severe disease with high death losses, but fortunately it is not normally found in the Unites States. This report describes an outbreak of highly pathogenic avian influenza in Chile. This was the first recorded case of the virus in South America. Although, the virus was most closely related genetically to H7avian influenza viruses from the United States, it was quite distinct from other characterized viruses. The virus was shown in experimental studies to be highly virulent for chickens. Fortunately the outbreak was controlled, and no further evidence for the disease circulating in Chile exists.
Technical Abstract: Influenza A viruses are thought to occur worldwide in wild birds and are occasionally associated with outbreaks in commercial chickens and turkeys. However, no isolations of avian influenza viruses have been reported from wild birds or poultry in South America. Recently an outbreak in chickens of H7N3 low pathogenic avian influenza (LPAI) occurred in Chile. One month later, after a sudden increase in mortality, a H7N3 highly pathogenic avian influenza (HPAI) virus was isolated. Sequence analysis of all eight genes of the LPAI virus and the HPAI viruses showed only minor differences between the viruses except at the hemagglutinin cleavage site. The LPAI virus had a cleavage site similar to other low pathogenic H7 viruses, but the HPAI isolates had a 30 nucleotide insert. The insertion appeared to have occurred by recombination between the HA and nucleoprotein genes of the low pathogenic virus resulting in a virulence shift. Sequence comparison of all eight gene segments showed the Chilean viruses were also quite distinct from all other avian influenza viruses and represent a distinct South American clade.