Submitted to: International Symposium on Avian Influenza
Publication Type: Abstract Only
Publication Acceptance Date: 2/5/2002
Publication Date: 4/17/2002
Technical Abstract: The H5N1 highly pathogenic avian influenza (HPAI) outbreak that occurred in Hong Kong in 1997 and the subsequent transmission of this virus from chickens to humans kindled the recognition of influenza A viruses as potentially zoonotic pathogens. This unique H5N1 avian influenza (AI) virus is unmatched in its ability to transmit directly from chickens to humans and cause both substantial disease in poultry as well as human disease and fatality. A repertoire of avian and mammalian species was intranasally inoculated with the A/chicken/Hong Kong/220/97 (H5N1) AI virus (chicken/HK) in order to ascertain which species are susceptible to infection with this virus and to determine the pathobiology of disease resultant from the infection. Parameters evaluated in order to determine the rate and results of infection in each species included the daily morbidity and mortality, gross and histological lesions, the distribution of viral antigen, and the frequency and titer of virus reisolation from selected tissues. A total of nineteen species were used in this investigation. Avian species included seven gallinaceous species, Pekin ducks (Anas platyrhynchos), Embden geese (Anser anser), emus (Dramaius novaehollandiae), pigeons (Columba livia), budgerigars (Melopsittacus undulatus), zebra finches (Taeniopygia guttata), and wild-captured house finches (Carpodacus mexicanus), house sparrows (Passer domesticus), European starlings (Sturnus vulgaris), and laughing gulls (Larus atricilla). Mammalian species included domestic rats and rabbits. Four gradations of disease were observed among these avian and mammalian species. These gradations included rapidly fatal systemic disease, severe neurological disease, asymptomatic infection to only mild transient disease, and an absence of clinical disease relative to only minimal or no productive viral replication. The species most susceptible to infection included the seven gallinaceous species and the zebra finches, each of which suffered significant morbidity and mortality due to the viral infection. The high pathogenicity of this virus for these species was confirmed by the demonstration of viral antigen in the vascular endothelium and parenchyma of multiple organs as well as the reisolation of high titers of virus from the brain, lung, and kidney. Species which suffered severe neurological disease with mortality included the budgerigars and house finches, whereas the geese and emus also developed severe neurological disease but lacked mortality within the 14 day investigative period. The chicken/HK virus was reisolated most consistently from the brain of these four species, indicating that clinical disease directly correlated to the presence of viral antigen. Pekin ducks, laughing gulls, and house sparrows could be infected with the virus. However, clinical disease was not observed in the ducks or gulls, and only mild transient depression was observed in the house sparrows. Additionally, histological lesions were mild, viral antigen was rare, and virus reisolation was only obtained infrequently from the lung and/or kidney from these three species, indicating that the infection of these species was largely self-limiting. In pigeons, starlings, rats, and rabbits, clinical disease was not observed, lesions and related viral antigen were absent in all examined tissues, and the virus was not or was only infrequently reisolated from the tissues collected. These results confirm that these species are largely resistant to infection with the chicken/HK virus. In total, this investigation demonstrates that the H5N1 Hong Kong-origin virus can display a broad range of virulence from apathogenic to highly pathogenic among these selected avian and mammalian species, and distinct differences can occur in the susceptibility of avian species, even those which are members of the same order.