Wild Waterfowl Research Articles

Avian Influenza Virus Surveillance in Hunter-Harvested Waterfowl, Texas Coast, September 2009–January 2010

Wild waterfowl are considered the natural reservoir of type A influenza viruses, and the migratory nature of many waterfowl species presents a possible vehicle for global dissemination of these infectious agents. In order to fully understand the ecology of influenza viruses, multiyear surveillance efforts are critical, particularly in understudied areas, such as waterfowl wintering areas. Herein we report results obtained during the fifth year ofa 5-yr avian influenza virus (AIV) surveillance project conducted on waterfowl wintering grounds of the Texas Coast. During year 5, the 2009-2010 hunting season (September, November-January), 655 cloacal swabs were collected from hunter-harvested waterfowl and screened for AIV by real-time RT-PCR (rRT-PCR) followed by virus isolation on all positive samples. Molecular methods were used for subtyping all AIV isolates. Sixty-five (9.5%) samples were positive for AIV by rRT-PCR, and 24 (3.7%) AIVs were isolated. Eight different hemagglutinin (H3, 4, 5, 6, 8, 9, 10, and 11) and seven different neuraminidase (N1, 2, 3, 4, 6, 8, and 9) subtypes were identified. This was the first year H8 and H9 were isolated throughout the 5-yr survey. Our results support the fact that continued multiyear surveillance of natural reservoirs, particularly in understudied areas, is needed in order to better understand the ecology of AIVs in nature.

Implementation of an Information System for the Traceability of Live Decoy Birds

In the Veneto region (northern Italy), some geographic areas in the Po Valley have a large concentration of industrial poultry farms and are located close to wet areas with high populations of wild waterfowl. Live decoy birds belonging to the orders of Anseriformes and Charadriiformes can constitute a "bridge" for avian influenza (AI) viruses between the wild reservoir and the rural holdings where live decoy birds are usually kept, sometimes together with poultry. Thus, the use of live decoy birds during bird hunting could increase the risk of exposure of poultry farms to AI viruses. Since 2008, this kind of hunting has been strictly regulated with regard to the detection and use of live decoy birds. In order to guarantee the application of appropriate AI risk-modulating and monitoring measures in the management of the live decoys according to the European Union (EU) provisions, a solid and well-structured information system has been created. The Regional Data Bank (RDB) of farms and livestock, which has been operating since 1997, also contains data on farms and poultry movements. Therefore, the RDB management software was updated to collect data from the hunters who keep live decoy birds, and specific functions were integrated to ensure the traceability of these birds. Each live decoy bird has been identified by an irremovable ring. The individual code of each ring is recorded in the RDB and linked to both the holder's code and the hunting area. Transfers and death/slaughtering of the registered birds are recorded, too. The activation of a computerized data collection system has proven to be a prerequisite for the implementation of a control system for live decoy birds and provides an essential tool for the management of AI emergencies.

Molecular Epidemiology of Outbreak-Associated and Wild-Waterfowl-Derived Newcastle Disease Virus Strains in Finland, Including a Novel Class I Genotype

Newcastle disease (ND) is a highly contagious, severe disease of poultry caused by pathogenic strains of Newcastle disease virus (NDV; or avian paramyxovirus-1). NDV is endemic in wild birds worldwide and one of the economically most important poultry pathogens. Most of the published strains are outbreak-associated strains, while the apathogenic NDV strains that occur in wild birds, posing a constant threat to poultry with their capability to convert into more virulent forms, have remained less studied. We screened for NDV RNA in cloacal and oropharyngeal samples from wild waterfowl in Finland during the years 2006 to 2010: 39 of 715 birds were positive (prevalence, 5.5%). The partial or full-length F genes of 37 strains were sequenced for phylogenetic purposes. We also characterized viruses derived from three NDV outbreaks in Finland and discuss the relationships between these outbreak-associated and the wild-bird-associated strains. We found that all waterfowl NDV isolates were lentogenic strains of class I or class II genotype I. We also isolated a genetically distinct class I strain (teal/Finland/13111/2008) grouping phylogenetically together with only strain HIECK87191, isolated in Northern Ireland in 1987. Together they seem to form a novel class I genotype genetically differing from other known NDVs by at least 12%.

Surveillance of Influenza A Virus in Wild Birds in the Asian Portion of Russia in 2008

Wild waterfowl undertake a variety of long-distance flights during their migration. These flights provide birds with the opportunities to both acquire and disseminate avian influenza viruses (AIVs). The Asian portion of Russia is crossed by four major migration routes and represents the major breeding area for many wild bird species in the Palearctic. The Asian territory of Russia plays an important role in distribution, persistence, and evolution of AIVs due to the ecologic relationships of bird populations from Russia and different Asian, European, African, and North American countries. Our study highlights the results of surveillance conducted in 2008 for AIVs in wild birds in the Asian portion of Russia. During this study, our team collected and tested 5678 samples from wild birds. Among them, 41 samples tested positive for AIV with an isolation rate of 0.72%. The highest AIV prevalence, 1.49%, was found in Anseriformes. In Ardeidae and Laridae, the AIV prevalence was 1.23% and 0.64%, respectively. Rallidae showed the lowest AIV prevalence of 0.61%. Phylogenetic analysis of H3 and H4 subtypes represented close relationships of AIVs isolated from the Asian portion of Russia to the AI strains from Asia, Africa, and Europe. These findings were confirmed by the wild bird migration routes that affect bird populations from Eurasian, African, Australian, and North American continents.

Quantitative exposure assessment of waterfowl hunters to avian influenza viruses

The potential for direct transmission of type A influenza viruses from wild waterfowl to humans is undefined. This study estimated exposure of hunters to avian influenza virus (AIV) resulting from direct contact with potentially infected waterfowl in Georgia (GA), Louisiana (LA) and Minnesota (MN), and demonstrated variation in the risk of exposure to AIV by hunting location and time. Hunting begins earlier in MN, starting in October, and later in GA and LA, usually starting in November. In addition, the numbers of hunters and birds harvested varies considerably in each state, with LA hosting the largest harvest in the USA Temporal effects resulted in variation of the exposure risk per hunter-day, with a higher risk associated with the earlier months of the hunting season. Exposure risk in locations varied due to AIV prevalence during each hunting season, average bird harvest per hunter-day, and ratio of juveniles/adult birds harvested (higher risk associated with higher ratios). Population risk is discussed based on the exposure risk and number of active hunters in each state per month. The risk of human exposure to AIV was also shown to be temporally distinct from the time of greatest risk of human influenza A infection during circulation of seasonal human influenza viruses, making recombination events due to co-infection unlikely.

Molecular characterization of H3N2 and H4N6 subtypes avian influenza viruses isolated from mallards in Poyang Lake, China in 2010

Poyang Lake is the largest inland freshwater lake in China and contains many species of wild birds and waterfowls. We conducted a survey of avian influenza viruses in nine semi-artificial waterfowl farms in Poyang Lake during January to March of 2010. Out of 1036 cloacal swabs collected, three H3N2 and one H4N6 influenza viruses were isolated from healthy mallards. All the isolates were genetically and phylogenetically characterized. The analysis of putative HA cleavage sites showed that all the four isolates possessed the molecular characteristics (QTRGL for H3N2 viruses, PEKASR for H4N6 virus) of lowly pathogenic avian influenza (LPAI) virus. The phylogenetic analysis of the viral genomes showed that all four virus isolates clustered in the Eurasian clade of influenza viruses. The M gene of the viruses possessed the highest homology with highly pathogenic H5N1 influenza viruses. In addition, co-infection of H3N2 and H4N6 in the same farm was observed. And interestingly, we isolated two subtypes viruses (H3N2 and H4N6) and their progeny virus (H3N2) with evidence of genome reassortment from the same farm, in which the PB1 and PB2 gene segments of H4N6 replaced those of the H3N2 strain. The results of animal infection experiments showed that all the four isolated viruses were lowly pathogenic to chickens and not pathogenic to mice, which was consistent with the results of genetic analysis.

Efficient isolation of avian bornaviruses (ABV) from naturally infected psittacine birds and identification of a new ABV genotype from a salmon-crested cockatoo (Cacatua moluccensis)

Avian bornaviruses (ABV) have been discovered in 2008 as the causative agent of proventricular dilatation disease (PDD) in psittacine birds. To date, six ABV genotypes have been described in psittacines. Furthermore, two additional but genetically different ABV genotypes were recognized in non-psittacine birds such as canary birds and wild waterfowl. This remarkable genetic diversity poses a considerable challenge to ABV diagnosis, since polymerase chain reaction (PCR) assays may fail to detect distantly related or as yet unknown genotypes. In this study we investigated the use of virus isolation in cell culture as a strategy for improving ABV diagnosis. We found that the quail fibroblast cell line CEC-32 allows very efficient isolation of ABV from psittacine birds. Isolation of ABV was successful not only from organ samples but also from cloacal and pharyngeal swabs and blood samples collected intra vitam from naturally infected parrots. Importantly, using this experimental approach we managed to isolate a new ABV genotype, termed ABV-7, from a salmon-crested cockatoo (Cacatua moluccensis). Phylogenetic analysis showed that ABV-7 is most closely related to the psittacine genotypes ABV-1, -2, -3, and -4 and clearly distinct from genotypes ABV-5 and -6. Our successful identification of ABV-7 emphasizes the necessity to consider the high genetic diversity when trying to diagnose ABV infections with high reliability and further shows that classical virus isolation may represent a useful diagnostic option, particularly for the detection of new ABV genotypes.

Low-pathogenic avian influenza virus A/turkey/Ontario/6213/1966 (H5N1) is the progenitor of highly pathogenic A/turkey/Ontario/7732/1966 (H5N9)

The first confirmed outbreak of highly pathogenic avian influenza (HPAI) virus infections in North America was caused by A/turkey/Ontario/7732/1966 (H5N9); however, the phylogeny of this virus is largely unknown. This study performed genomic sequence analysis of 11 avian influenza isolates from 1956 to 1979 for comparison with A/turkey/Ontario/7732/1966 (H5N9). Phylogenetic and genetic analyses included these viruses in combination with all known full-genome sequences of avian viruses isolated before 1981. It was shown that a low-pathogenic avian influenza virus, A/turkey/Ontario/6213/1966 (H5N1), that had been isolated 3 months previously, was the closest known genetic relative with six genome segments of common lineage encoding the polymerase subunits PB2, PB1 and PA, nucleoprotein (NP), haemagglutinin (HA) and non-structural (NS) proteins. The lineages of these genome segments included reassortment with other North American turkey viruses that were all rooted in North American wild waterfowl with the HA gene originating from the H5N2 serotype. The phylogenies demonstrated adaptation from North American wild birds to turkeys with the possible involvement of domestic waterfowl. The turkey isolate, A/turkey/Wisconsin/1968 (H5N9), was the second most closely related poultry isolate to A/turkey/Ontario/7732/1966 (H5N9), possessing five common lineage genome segments (PB2, PB1, PA, HA and neuraminidase). The A/turkey/Ontario/6213/1966 (H5N1) virus was more virulent than A/turkey/Wisconsin/68 (H5N9) for chicken embryos and mice, indicating a greater biological similarity to A/turkey/Ontario/7732/1966 (H5N9). Thus, A/turkey/Ontario/6213/1966 (H5N1) was identified as the closest known ancestral relative of HPAI A/turkey/Ontario/7732/1966 (H5N9), which will serve as a useful reference virus for characterizing the early genetic and biological properties associated with the emergence of pathogenic avian influenza strains.

Environmental and demographic determinants of avian influenza viruses in waterfowl across the contiguous United States.

Outbreaks of avian influenza in North American poultry have been linked to wild waterfowl. A first step towards understanding where and when avian influenza viruses might emerge from North American waterfowl is to identify environmental and demographic determinants of infection in their populations. Laboratory studies indicate water temperature as one determinant of environmental viral persistence and we explored this hypothesis at the landscape scale. We also hypothesized that the interval apparent prevalence in ducks within a local watershed during the overwintering season would influence infection probabilities during the following breeding season within the same local watershed. Using avian influenza virus surveillance data collected from 19,965 wild waterfowl across the contiguous United States between October 2006 and September 2009 We fit Logistic regression models relating the infection status of individual birds sampled on their breeding grounds to demographic characteristics, temperature, and interval apparent prevalence during the preceding overwintering season at the local watershed scale. We found strong support for sex, age, and species differences in the probability an individual duck tested positive for avian influenza virus. In addition, we found that for every seven days the local minimum temperature fell below zero, the chance an individual would test positive for avian influenza virus increased by 5.9 percent. We also found a twelve percent increase in the chance an individual would test positive during the breeding season for every ten percent increase in the interval apparent prevalence during the prior overwintering season. These results suggest that viral deposition in water and sub-freezing temperatures during the overwintering season may act as determinants of individual level infection risk during the subsequent breeding season. Our findings have implications for future surveillance activities in waterfowl and domestic poultry populations. Further study is needed to identify how these drivers might interact with other host-specific infection determinants, such as species phylogeny, immunological status, and behavioral characteristics.

A Simple Stochastic Model with Environmental Transmission Explains Multi-Year Periodicity in Outbreaks of Avian Flu

Avian influenza virus reveals persistent and recurrent outbreaks in North American wild waterfowl, and exhibits major outbreaks at 2–8 years intervals in duck populations. The standard susceptible-infected- recovered (SIR) framework, which includes seasonal migration and reproduction, but lacks environmental transmission, is unable to reproduce the multi-periodic patterns of avian influenza epidemics. In this paper, we argue that a fully stochastic theory based on environmental transmission provides a simple, plausible explanation for the phenomenon of multi-year periodic outbreaks of avian flu. Our theory predicts complex fluctuations with a dominant period of 2 to 8 years which essentially depends on the intensity of environmental transmission. A wavelet analysis of the observed data supports this prediction. Furthermore, using master equations and van Kampen system-size expansion techniques, we provide an analytical expression for the spectrum of stochastic fluctuations, revealing how the outbreak period varies with the environmental transmission.

Avian Cholera, a Threat to the Viability of an Arctic Seabird Colony?

Evidence that infectious diseases cause wildlife population extirpation or extinction remains anecdotal and it is unclear whether the impacts of a pathogen at the individual level can scale up to population level so drastically. Here, we quantify the response of a Common eider colony to emerging epidemics of avian cholera, one of the most important infectious diseases affecting wild waterfowl. We show that avian cholera has the potential to drive colony extinction, even over a very short period. Extinction depends on disease severity (the impact of the disease on adult female survival) and disease frequency (the number of annual epidemics per decade). In case of epidemics of high severity (i.e., causing >30% mortality of breeding females), more than one outbreak per decade will be unsustainable for the colony and will likely lead to extinction within the next century; more than four outbreaks per decade will drive extinction to within 20 years. Such severity and frequency of avian cholera are already observed, and avian cholera might thus represent a significant threat to viability of breeding populations. However, this will depend on the mechanisms underlying avian cholera transmission, maintenance, and spread, which are currently only poorly known.

Presence of Avian Influenza Viruses in Waterfowl and Wetlands during Summer 2010 in California: Are Resident Birds a Potential Reservoir?

Although wild waterfowl are the main reservoir for low pathogenic avian influenza viruses (LPAIv), the environment plays a critical role for the circulation and persistence of AIv. LPAIv may persist for extended periods in cold environments, suggesting that waterfowl breeding areas in the northern hemisphere may be an important reservoir for AIv in contrast to the warmer southern wintering areas. We evaluated whether southern wetlands, with relatively small populations (thousands) of resident waterfowl, maintain AIv in the summer, prior to the arrival of millions of migratory birds. We collected water and fecal samples at ten wetlands in two regions (Yolo Bypass and Sacramento Valley) of the California Central Valley during three bi-weekly intervals beginning in late July, 2010. We detected AIv in 29/367 fecal samples (7.9%) and 12/597 water samples (2.0%) by matrix real time Reverse Transcription Polymerase Chain Reaction (rRT-PCR). We isolated two H3N8, two H2N3, and one H4N8 among rRT-PCR positive fecal samples but no live virus from water samples. Detection of AIv RNA in fecal samples was higher from wetlands in the Sacramento Valley (11.9%) than in the Yolo Bypass (0.0%), but no difference was found for water samples (2.7 vs. 1.7%, respectively). Our study showed that low densities of hosts and unfavorable environmental conditions did not prevent LPAIv circulation during summer in California wetlands. Our findings justify further investigations to understand AIv dynamics in resident waterfowl populations, compare AIv subtypes between migratory and resident waterfowl, and assess the importance of local AIv as a source of infection for migratory birds.

The role of nuclear technologies in the diagnosis and control of livestock diseases—a review

Nuclear and nuclear-related technologies have played an important role in animal health, particularly in relation to disease diagnosis and characterization of pathogenic organisms. This review focuses primarily on how and where nuclear technologies, both non-isotopic and isotopic methods, have made their impact in the past and where it might be expected they could have an impact in the future. The review outlines the extensive use of radiation attenuation in attempts to create vaccines for a multiplicity of pathogenic organisms and how the technology is being re-examined in the light of recent advances in irradiation techniques and cryopreservation/lyophilization that might obviate some of the problems of maintenance of viable, attenuate vaccines and their transport and use in the field. This approach could be used for a number of parasitic diseases where vaccination has been problematic and where investigations into the development of molecular vaccines have still failed to deliver satisfactory candidates for generating protective immune responses. Irradiation of antigens or serum samples also has its uses in diagnosis, especially when the samples need to be transported across international boundaries, or when handling the pathogens in question when carrying out a test presents serious health hazards to laboratory personnel. The present-day extensive use of enzyme immunoassays and molecular methods (e.g., polymerase chain reaction) for diagnosis and characterization of animal pathogens has its origins in the use of isotope-labeled antigens and antibodies. These isotopic techniques that included the use of 75Se, 32P, 125I, and 35S isotopes enabled a level of sensitivity and specificity that was hitherto unrealized, and it is prescient to remind ourselves of just how successful these technologies were, in spite of their infrequent use nowadays. Finally, the review looks at the potential for stable isotope analysis for a variety of applications—in the tracking of animal migrations, where the migrant are potential carriers of transboundary animal diseases, and where it would be useful to determine the origins of the carrier, e.g., Highly Pathogenic Avian Influenza and its dissemination by wild water fowl. Other applications could be in monitoring sequestered microbial culture (e.g., rinderpest virus) where in the case of accidental or deliberate release of infective culture it would be possible to identify the laboratory from which the isolate originated.

Susceptibility of avian influenza viruses of the N6 subtype to the neuraminidase inhibitor oseltamivir

Avian influenza viruses are a source of genetic material that can be transmitted to humans through direct introduction or reassortment. Although there is a wealth of information concerning global monitoring for antiviral resistance among human viruses of the N1 and N2 neuraminidase (NA) subtypes, information concerning avian viruses of these and other NA subtypes is limited. We undertook a surveillance study to investigate the antiviral susceptibility of avian influenza N6 NA viruses, the predominant subtype among wild waterfowl. We evaluated 73 viruses from North American ducks and shorebirds for susceptibility to the NA inhibitor oseltamivir in a fluorescence-based NA enzyme inhibition assay. Most (90%) had mean IC50 values ranging from <0.01 to 5.0nM; 10% were from 5.1 to 50.0nM; and none were >50.0nM. Susceptibility to oseltamivir remained stable among all isolates collected over approximately three decades (P⩽0.74). Two isolates with I222V NA substitution had moderately reduced susceptibility to oseltamivir in vitro (IC50, 30.0 and 40.0nM). One field sample was a mixed population containing an avian paramyxovirus (APMV) and H4N6 influenza virus, as revealed by electron microscopy and hemagglutination inhibition assays with a panel of anti-APMV antisera. This highlights the importance of awareness and careful examination of non-influenza pathogens in field samples from avian sources. This study showed that oseltamivir-resistant N6 NA avian influenza viruses are rare, and must be tested both phenotypically and genotypically to confirm resistance.

The Effect of Swab Sample Choice on the Detection of Avian Influenza in Apparently Healthy Wild Ducks

Historically, avian influenza viruses have been isolated from cloacal swab specimens, but recent data suggest that the highly pathogenic avian influenza (HPAI) H5N1 virus can be better detected from respiratory tract specimens. To better understand how swab sample type affects the detection ability of low pathogenic avian influenza (LPAI) viruses we collected and tested four swab types: oropharyngeal swabs (OS), cloacal swabs (CS), the two swab types combined in the laboratory (LCS), and the two swab types combined in the field (FCS). A total of 1968 wild waterfowl were sampled by each of these four methods and tested for avian influenza virus using matrix gene reverse-transcription (RT)-PCR. The highest detection rate occurred with the FCS (4.3%) followed by the CS (4.0%). Although this difference did not achieve traditional statistical significance, Bayesian analysis indicated that FCS was superior to CS with an 82% probability. The detection rates for both the LCS (2.4%) and the OS (0.4%) were significantly different from the FCS. In addition, every swab type that was matrix RT-PCR positive was also tested for recovery of viable influenza virus. This protocol reduced the detection rate, but the ordering of swab types remained the same: 1.73% FCS, 1.42% CS, 0.81% LCS, and 0% OS. Our data suggest that the FCS performed at least as well as any other swab type for detecting LPAI viruses in the wild ducks tested. When considering recent studies showing that HPAI H5N1 can be better detected in the respiratory tract, the FCS is the most appropriate sample to collect for HPAI H5N1 surveillance while not compromising LPAI studies.

Genetic characterization of low pathogenic H5N1 and co-circulating avian influenza viruses in wild mallards (Anas platyrhynchos) in Belgium, 2008

As part of a long-term wild bird monitoring programme, five different low pathogenic (LP) avian influenza viruses (AIVs) were isolated from wild mallards (subtypes H1N1, H4N6, H5N1, H5N3, and H10N7). A LP H5N1 and two co-circulating (same location, same time period) viruses were selected for full genome sequencing. An H1N1 (A/Anas platyrhynchos/Belgium/09-762/2008) and an H5N1 virus (A/Anas platyrhynchos/Belgium/09-762-P1/2008) were isolated on the same day in November 2008, then an H5N3 virus (A/Anas platyrhynchos/09-884/2008) 5 days later in December 2008. All genes of these co-circulating viruses shared common ancestors with recent (2001 to 2007) European wild waterfowl influenza viruses. The H5N1 virus shares genome segments with both the H1N1 (PB1, NA, M) and the H5N3 (PB2, HA) viruses, and all three viruses share the same NS sequence. A double infection with two different PA segments from H5N1 and from H5N3 could be observed for the H1N1 sample. The observed gene constellations resulted from multiple reassortment events between viruses circulating in wild birds in Eurasia. Several internal gene segments from these 2008 viruses and the N3 sequence from the H5N3 show homology with sequences from 2003 H7 outbreaks in Italy (LP) and the Netherlands (highly pathogenic). These data contribute to the growing sequence evidence of the dynamic nature of the avian influenza natural reservoir in Eurasia, and underline the importance of monitoring AIV in wild birds. Genetic information of potential hazard to commercial poultry continues to circulate in this reservoir, including H5 and H7 subtype viruses and genes related to previous AIV outbreaks.

Persistence of influenza A viruses in relation with environmental factors

Wild waterfowl represents the natural reservoir of influenza A viruses. Transmission within bird populations occurs through an indirect fecal-oral route implying contaminated water. Within human populations, influenza A viruses can be transmitted through large droplets, aerosols, or direct contact with secretions. Thus, in the human compartment as in the avian one, influenza A viruses have to experiment a free living stage. The knowledge of factors influencing viral persistence during that key step is needed to understand their transmission dynamic. Data gathered here describe the major role played by temperature, pH and salinity on viral persistence in aquatic environment and the importance of UV radiations, humidity and temperature in mid air. We discuss mechanisms underlying these roles and the potential influence of other factors. We point out the need to develop researches to improve our understanding on influenza A virus stability and thus transmission.

Effects of Infection-Induced Migration Delays on the Epidemiology of Avian Influenza in Wild Mallard Populations

Wild waterfowl populations form a natural reservoir of Avian Influenza (AI) virus, and fears exist that these birds may contribute to an AI pandemic by spreading the virus along their migratory flyways. Observational studies suggest that individuals infected with AI virus may delay departure from migratory staging sites. Here, we explore the epidemiological dynamics of avian influenza virus in a migrating mallard (Anas platyrhynchos) population with a specific view to understanding the role of infection-induced migration delays on the spread of virus strains of differing transmissibility. We develop a host-pathogen model that combines the transmission dynamics of influenza with the migration, reproduction and mortality of the host bird species. Our modeling predicts that delayed migration of individuals influences both the timing and size of outbreaks of AI virus. We find that (1) delayed migration leads to a lower total number of cases of infection each year than in the absence of migration delay, (2) when the transmission rate of a strain is high, the outbreak starts at the staging sites at which birds arrive in the early part of the fall migration, (3) when the transmission rate is low, infection predominantly occurs later in the season, which is further delayed when there is a migration delay. As such, the rise of more virulent AI strains in waterfowl could lead to a higher prevalence of infection later in the year, which could change the exposure risk for farmed poultry. A sensitivity analysis shows the importance of generation time and loss of immunity for the effect of migration delays. Thus, we demonstrate, in contrast to many current transmission risk models solely using empirical information on bird movements to assess the potential for transmission, that a consideration of infection-induced delays is critical to understanding the dynamics of AI infection along the entire flyway.

Phylogenetic Analysis of H6 Influenza Viruses Isolated from Rosy-Billed Pochards (Netta peposaca) in Argentina Reveals the Presence of Different HA Gene Clusters

Until recently, influenza A viruses from wild waterfowl in South America were rarely isolated and/or characterized. To explore the ecology of influenza A viruses in this region, a long-term surveillance program was established in 2006 for resident and migratory water birds in Argentina. We report the characterization of 5 avian influenza viruses of the H6 hemagglutinin (HA) subtype isolated from rosy-billed pochards (Netta peposaca). Three of these viruses were paired to an N2 NA subtype, while the other two were of the N8 subtype. Genetic and phylogenetic analyses of the internal gene segments revealed a close relationship with influenza viruses from South America, forming a unique clade and supporting the notion of independent evolution from influenza A viruses in other latitudes. The presence of NS alleles A and B was also identified. The HA and NA genes formed unique clades separate from North American and Eurasian viruses, with the exception of the HA gene of one isolate, which was more closely related to the North American lineage, suggesting possible interactions between viruses of North American and South American lineages. Animal studies suggested that these Argentine H6 viruses could replicate and transmit inefficiently in chickens, indicating limited adaptation to poultry. Our results highlight the importance of continued influenza virus surveillance in wild birds of South America, especially considering the unique evolution of these viruses.

Characterization of an H4N2 avian influenza virus isolated from domestic duck in Dongting Lake wetland in 2009

In January 2009, an H4N2 subtype of avian influenza virus [A/duck/Hunan/8-19/2009 (H4N2)] was isolated from domestic ducks in Dongting Lake wetland. The whole genome of the virus was sequenced and the results indicated that multiple gene segments of the virus had a high homology with viruses isolated from wild waterfowl, which indicated that the virus was probably transmitted from wild waterfowl to domestic ducks. Phylogenetic analysis revealed that the each gene belonged to the Eurasian lineage of avian influenza viruses, but genetic reassortment occurs between viruses of different subtypes.