Susceptibility of N. American Ducks, Gulls to H5N1 Avian Influenza Viruses
Susceptibility of N. American Ducks, Gulls to H5N1 Avian Influenza Viruses
Since 2002‚ H5N1 highly pathogenic avian influenza (HPAI) viruses have been associated with deaths in numerous wild avian species throughout Eurasia. We assessed the clinical response and extent and duration of viral shedding in 5 species of North American ducks and laughing gulls (Larus atricilla) after intranasal challenge with 2 Asian H5N1 HPAI viruses. Birds were challenged at ≈10 to 16 weeks of age‚ consistent with temporal peaks in virus prevalence and fall migration. All species were infected‚ but only wood ducks (Aix sponsa) and laughing gulls exhibited illness or died. Viral titers were higher in oropharyngeal swabs than in cloacal swabs. Duration of viral shedding (1–10 days) increased with severity of clinical disease. Both the hemagglutination-inhibition (HI) and agar gel precipitin (AGP) tests were able to detect postinoculation antibodies in surviving wood ducks and laughing gulls; the HI test was more sensitive than the AGP in the remaining 4 species.
Free-living birds in the orders Anseriformes (ducks‚ geese‚ swans) and Charadriiformes (gulls‚ terns‚ shore birds) have traditionally been considered the natural reservoirs for avian influenza viruses (AIVs). However‚ before 2005‚ no evidence showed that highly pathogenic avian influenza (HPAI) viruses were maintained in wild bird populations. Rather‚ HPAI viruses evolved independent of wildlife reservoirs when wild-type AIVs were introduced and adapted to domestic poultry populations. One exception occurred in 1961 when a high proportion of deaths in common terns (Sterna hirundo) in South Africa was attributed to an H5N3 HPAI virus without evidence of prior infection in domestic poultry. However‚ this tern epizootic was limited‚ and the virus did not become endemic in any wild bird population.
In 2002‚ a substantial number of deaths associated with H5N1 HPAI virus infection were reported in captive ducks‚ geese‚ and flamingos housed within 2 waterfowl parks in Hong Kong Special Administrative Region‚ People’s Republic of China. Free-living gray herons (Ardea cinerea) and black-headed gulls (Larus ridbundus) also died during these outbreaks. Since 2002‚ sporadic deaths in wild birds‚ associated with H5N1 HPAI‚ have continued. Beginning in spring 2005‚ H5N1 HPAI outbreaks involving large numbers of wild birds were reported‚ and the subsequent spread of these viruses to Europe and Africa suggests that migratory birds may have been responsible for the long-range movement of these viruses. However‚ which wild avian species are important in H5N1 HPAI movement and whether these viruses will be established in free-living avian populations is unknown. The goal of this study was to determine the susceptibility of critical species of North American waterfowl to 2 H5N1 HPAI viruses and the potential impact of these species on the epidemiology of the viruses in North America.
Abstract and Introduction
Abstract
Since 2002‚ H5N1 highly pathogenic avian influenza (HPAI) viruses have been associated with deaths in numerous wild avian species throughout Eurasia. We assessed the clinical response and extent and duration of viral shedding in 5 species of North American ducks and laughing gulls (Larus atricilla) after intranasal challenge with 2 Asian H5N1 HPAI viruses. Birds were challenged at ≈10 to 16 weeks of age‚ consistent with temporal peaks in virus prevalence and fall migration. All species were infected‚ but only wood ducks (Aix sponsa) and laughing gulls exhibited illness or died. Viral titers were higher in oropharyngeal swabs than in cloacal swabs. Duration of viral shedding (1–10 days) increased with severity of clinical disease. Both the hemagglutination-inhibition (HI) and agar gel precipitin (AGP) tests were able to detect postinoculation antibodies in surviving wood ducks and laughing gulls; the HI test was more sensitive than the AGP in the remaining 4 species.
Introduction
Free-living birds in the orders Anseriformes (ducks‚ geese‚ swans) and Charadriiformes (gulls‚ terns‚ shore birds) have traditionally been considered the natural reservoirs for avian influenza viruses (AIVs). However‚ before 2005‚ no evidence showed that highly pathogenic avian influenza (HPAI) viruses were maintained in wild bird populations. Rather‚ HPAI viruses evolved independent of wildlife reservoirs when wild-type AIVs were introduced and adapted to domestic poultry populations. One exception occurred in 1961 when a high proportion of deaths in common terns (Sterna hirundo) in South Africa was attributed to an H5N3 HPAI virus without evidence of prior infection in domestic poultry. However‚ this tern epizootic was limited‚ and the virus did not become endemic in any wild bird population.
In 2002‚ a substantial number of deaths associated with H5N1 HPAI virus infection were reported in captive ducks‚ geese‚ and flamingos housed within 2 waterfowl parks in Hong Kong Special Administrative Region‚ People’s Republic of China. Free-living gray herons (Ardea cinerea) and black-headed gulls (Larus ridbundus) also died during these outbreaks. Since 2002‚ sporadic deaths in wild birds‚ associated with H5N1 HPAI‚ have continued. Beginning in spring 2005‚ H5N1 HPAI outbreaks involving large numbers of wild birds were reported‚ and the subsequent spread of these viruses to Europe and Africa suggests that migratory birds may have been responsible for the long-range movement of these viruses. However‚ which wild avian species are important in H5N1 HPAI movement and whether these viruses will be established in free-living avian populations is unknown. The goal of this study was to determine the susceptibility of critical species of North American waterfowl to 2 H5N1 HPAI viruses and the potential impact of these species on the epidemiology of the viruses in North America.
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