Submitted to: Options for the Control of Influenza Conference
Publication Type: Abstract Only
Publication Acceptance Date: November 10, 2000
Publication Date: September 23, 2000
Technical Abstract: The H7N7 subtype of virus has been associated with disease in mammals on at least five different occasions. This includes the endemic infection of horses (equine type 1 influenza), and the introduction on four separate occasions of H7N7 avian influenza viruses infecting humans. Although in the four occurrences of infection of humans by avian influenza viruses, only a single individual or a limited number of people were infected. The viruses include FPV/Weybridge, Steele/59, Seal/MA/1/80, and England/268/96. Three of the cases resulted in only mild disease, primarily conjunctivitis. Two of these three cases were naturally acquired infections while the third was a laboratory acquired infection (FPV/Weybridge). The Steele/59 virus was associated with more serious clinical signs of acute hepatitis, but the patient also made a full recovery. Sequence analysis of all four viruses demonstrated additional amino acids at the hemagglutinin cleavage site in two of the viruses, FPV/Weybridge and Steele/59. The addition of basic amino acids at the cleavage site is associated with the highly pathogenic phenotype in poultry, and both of these isolates were highly pathogenic for poultry in standard pathotyping tests. Based on sequence comparisons, two of the viruses were of North American avian origin, while the other two viruses were of Eurasian origin. Several of the viruses were also examined by mouse inoculation, and one of the viruses was virulent in mice.