Mapping the risk of avian influenza in wild birds in the US

Abstract

BackgroundAvian influenza virus (AIV) is an important public health issue because pandemic influenza viruses in people have contained genes from viruses that infect birds. The H5 and H7 AIV subtypes have periodically mutated from low pathogenicity to high pathogenicity form. Analysis of the geographic distribution of AIV can identify areas where reassortment events might occur and how high pathogenicity influenza might travel if it enters wild bird populations in the US. Modelling the number of AIV cases is important because the rate of co-infection with multiple AIV subtypes increases with the number of cases and co-infection is the source of reassortment events that give rise to new strains of influenza, which occurred before the 1968 pandemic. Aquatic birds in the orders Anseriformes and Charadriiformes have been recognized as reservoirs of AIV since the 1970s. However, little is known about influenza prevalence in terrestrial birds in the order Passeriformes. Since passerines share the same habitat as poultry, they may be more effective transmitters of the disease to humans than aquatic birds. We analyze 152 passerine species including the American Robin (Turdus migratorius) and Swainson's Thrush (Catharus ustulatus).MethodsWe formulate a regression model to predict AIV cases throughout the US at the county scale as a function of 12 environmental variables, sampling effort, and proximity to other counties with influenza outbreaks. Our analysis did not distinguish between types of influenza, including low or highly pathogenic forms.ResultsAnalysis of 13,046 cloacal samples collected from 225 bird species in 41 US states between 2005 and 2008 indicates that the average prevalence of influenza in passerines is greater than the prevalence in eight other avian orders. Our regression model identifies the Great Plains and the Pacific Northwest as high-risk areas for AIV. Highly significant predictors of AIV include the amount of harvested cropland and the first day of the year when a county is snow free.ConclusionsAlthough the prevalence of influenza in waterfowl has long been appreciated, we show that 22 species of song birds and perching birds (order Passeriformes) are influenza reservoirs in the contiguous US.

Cross-Seasonal Patterns of Avian Influenza Virus in Breeding and Wintering Migratory Birds: A Flyway Perspective

“…This concentration of overwintering sites that support over 6 million birds each winter in the CCV (Reid and Heitmeyer 1995) may facilitate intermingling of different species originating from various breeding grounds, resulting in exchange of subtypes. This is consistent with studies that have modeled AIV risk in North America and concluded that agriculture is an important predictor of outbreaks (Fuller et al 2010). Our data suggest that the CCV may be an important mixing bowl for AIV subtypes that circulate along the Pacific Flyway, with implications for the reassortment and evolution of the virus.…”

Prevalence of avian influenza viruses, Mycobacterium avium, and Mycobacterium avium, subsp. paratuberculosis in marsh-dwelling passerines in Slovakia, 2008

“…Studies of AIV ecology in wild birds from North America have also shown seasonal changes and between-year fluctuations in prevalence and subtype distribution (Webster et al 1992;Krauss et al 2004). Recently, it has been suggested that birds from the order Passeriformes could act as influenza reservoirs (Fuller et al 2010), and our results support this. A total of 9.1% of swabs taken from birds caught in April 2008, and a single sample (0.8%) taken from birds caught in June/July, tested positive for M. avium (Tables 1, 2).…”

Avian Influenza Viruses in Wild Land Birds in Northern Vietnam

“…While reports of LPAI H5 viruses in passerines are infrequent relative to waterfowl, this is an important order from which isolates of AIVs from wild-caught animals have been made (reviewed by Stallknecht et al, 2007). In either case our results suggest that wild passerines could play a role in circulating AIVs in the environment in northern Vietnam, as the birds move locally or as they share habitat with domestic birds (Fuller et al, 2010).…”

“…While most affected wild bird species inhabit wetlands or aquatic habitats (Olsen et al, 2006;Stallknecht and Brown, 2007), HPAI H5N1 has been isolated from wildcaught passerines including live Eurasian Tree Sparrows in China (Kou et al, 2005) and a dead one in Hong Kong (Ellis et al, 2004). A recent HPAI H5N1 isolate from a tree sparrow linked to limited transmission among humans in China (Liu et al, 2010) and a relatively high prevalence of AIVs in passerines in the USA (Fuller et al, 2010) also motivate a closer look at the occurrence of AIVs in wild-caught passerines. Little information is available about the occurrence of AIVs in wild-caught birds in Southeast Asia, including Vietnam, an area experiencing a relatively high incidence of outbreaks in humans and domestic poultry (Alexander, 2007;Hien et al, 2009;Brown, 2010).…”