Avian Influenza Viruses In Wild Birds Research Articles

Avian Influenza in Wild Birds from South America: Review, Implications and Perspectives

Avian influenza viruses (AIVs) have been recorded in a broad variety of hosts, including humans, terrestrial and marine mammals, and domestic and wild birds. Wild aquatic birds are recognized as the chief natural reservoirs of AIV, and their migratory flyways can serve as routes for the dispersion of the virus across countries and continents. Although AIV is one of the most studied pathogens in the world, studies on the ecology and epidemiology of this virus in South America are few and fragmented. In this review, we examine the current state of the art on the epidemiology of AIV in wild birds in South America. Current evidence corroborates that many of the broad epidemiological patterns that have been documented in other continents, such as the role played by Anseriformes and Charadriiformes in the maintenance and spread of AIV, are also true in South America. On the other hand, the fact that AIV prevalence in South American studies appears to be remarkably lower than that observed in other continents, along with the presence of endemic taxa of birds that may be highly susceptible to AIV, indicates that South America may have distinct characteristics that modulate the epidemiology of AIV in unique ways. However, our knowledge on the occurrence of AIV in South America is still limited and there are important gaps in the species and geographic distribution of the sampling effort.

Novel avian influenza A (H5N6) viruses isolated in migratory waterfowl before the first human case reported in China, 2014

In May 2014, China formally confirmed the first human infection with the novel H5N6 avian influenza virus (AIV) in Sichuan Province. Before the first human case was reported, surveillance of AIVs in wild birds resulted in the detection of three H5N6 viruses in faecal samples from migratory waterfowl in Chenhu wetlands, Hubei Province, China. Genetic and phylogenetic analyses revealed that these three novel viruses were closely related to the H5N6 virus that has caused human infections in China since 2014. A Bayesian phylogenetic reconstruction of all eight segments suggests multiple reassortment events in the evolution of these viruses. The hemagglutinin (HA) and neuraminidase (NA) originated from the H5N2 and H6N6 AIVs, respectively, whereas all six internal genes were derived from avian H5N1 viruses. The reassortant may have occurred in eastern China during 2012–2013. A phylogeographic analysis of the HA and NA genes traced the viruses to southern China, from where they spread to other areas via eastern China. A receptor-binding test showed that H5N6 viruses from migratory waterfowl had human-type receptor-binding activity, suggesting a potential for transmission to humans. These data suggest that migratory waterfowl may play a role in the dissemination of novel H5N6 viruses.

Isolation and Genetic Characterization of Avian Influenza Viruses Isolated from Wild Birds in the Azov-Black Sea Region of Ukraine (2001-2012).

Wild bird surveillance for avian influenza virus (AIV) was conducted from 2001 to 2012 in the Azov - Black Sea region of the Ukraine, considered part of the transcontinental wild bird migration routes from northern Asia and Europe to the Mediterranean, Africa, and southwest Asia. A total of 6281 samples were collected from wild birds representing 27 families and eight orders for virus isolation. From these samples, 69 AIVs belonging to 15 of the 16 known hemagglutinin (HA) subtypes and seven of nine known neuraminidase (NA) subtypes were isolated. No H14, N5, or N9 subtypes were identified. In total, nine H6, eight H1, nine H5, seven H7, six H11, six H4, five H3, five H10, four H8, three H2, three H9, one H12, one H13, one H15, and one H16 HA subtypes were isolated. As for the NA subtypes, twelve N2, nine N6, eight N8, seven N7, six N3, four N4, and one undetermined were isolated. There were 27 HA and NA antigen combinations. All isolates were low pathogenic AIV except for eight highly pathogenic (HP) AIVs that were isolated during the H5N1 HPAI outbreaks of 2006-08. Sequencing and phylogenetic analysis of the HA genes revealed epidemiological connections between the Azov-Black Sea regions and Europe, Russia, Mongolia, and Southeast Asia. H1, H2, H3, H7, H8, H6, H9, and H13 AIV subtypes were closely related to European, Russian, Mongolian, and Georgian AIV isolates. H10, H11, and H12 AIV subtypes were epidemiologically linked to viruses from Europe and Southeast Asia. Serology conducted on serum and egg yolk samples also demonstrated previous exposure of many wild bird species to different AIVs. Our results demonstrate the great genetic diversity of AIVs in wild birds in the Azov-Black Sea region as well as the importance of this region for monitoring and studying the ecology of influenza viruses. This information furthers our understanding of the ecology of avian influenza viruses in wild bird species.

Molecular Characterization of Subtype H11N9 Avian Influenza Virus Isolated from Shorebirds in Brazil.

Migratory aquatic birds play an important role in the maintenance and spread of avian influenza viruses (AIV). Many species of aquatic migratory birds tend to use similar migration routes, also known as flyways, which serve as important circuits for the dissemination of AIV. In recent years there has been extensive surveillance of the virus in aquatic birds in the Northern Hemisphere; however in contrast only a few studies have been attempted to detect AIV in wild birds in South America. There are major flyways connecting South America to Central and North America, whereas avian migration routes between South America and the remaining continents are uncommon. As a result, it has been hypothesized that South American AIV strains would be most closely related to the strains from North America than to those from other regions in the world. We characterized the full genome of three AIV subtype H11N9 isolates obtained from ruddy turnstones (Arenaria interpres) on the Amazon coast of Brazil. For all gene segments, all three strains consistently clustered together within evolutionary lineages of AIV that had been previously described from aquatic birds in North America. In particular, the H11N9 isolates were remarkably closely related to AIV strains from shorebirds sampled at the Delaware Bay region, on the Northeastern coast of the USA, more than 5000 km away from where the isolates were retrieved. Additionally, there was also evidence of genetic similarity to AIV strains from ducks and teals from interior USA and Canada. These findings corroborate that migratory flyways of aquatic birds play an important role in determining the genetic structure of AIV in the Western hemisphere, with a strong epidemiological connectivity between North and South America.

Avian influenza virus ecology in Iceland shorebirds: Intercontinental reassortment and movement

Shorebirds are a primary reservoir of avian influenza viruses (AIV). We conducted surveillance studies in Iceland shorebird populations for 3years, documenting high serological evidence of AIV exposure in shorebirds, primarily in Ruddy Turnstones (Arenaria interpres; seroprevalence=75%). However, little evidence of virus infection was found in these shorebird populations and only two turnstone AIVs (H2N7; H5N1) were able to be phylogenetically examined. These analyses showed that viruses from Iceland shorebirds were primarily derived from Eurasian lineage viruses, yet the H2 hemagglutinin gene segment was from a North American lineage previously detected in a gull from Iceland the previous year. The H5N1 virus was determined to be low pathogenic, however the PB2 gene was closely related to the PB2 from highly pathogenic H5N1 isolates from China. Multiple lines of evidence suggest that the turnstones were infected with at least one of these AIV while in Iceland and confirm Iceland as an important location where AIV from different continents interact and reassort, creating new virus genomes. Mounting data warrant continued surveillance for AIV in wild birds in the North Atlantic, including Canada, Greenland, and the northeast USA to determine the risks of new AI viruses and their intercontinental movement in this region.

Adaptive evolution and environmental durability jointly structure phylodynamic patterns in avian influenza viruses.

Author SummaryHuman populations have experienced several pandemics involving new subtypes of influenza virus over the past century. All of these pandemic strains contained gene segments that originated in wild birds, a host pool that supports a very large and genetically diverse array of influenza viruses. However, once an avian strain establishes itself within the human population, the genetic diversity of the resulting human subtypes is typically quite low compared to that of their avian counterparts. Here we compare the evolutionary dynamics of human and avian influenza viruses in North America and test different hypotheses that might explain these two contrasting evolutionary patterns. Our analysis shows that a combination of characteristics of the host (especially demography) and virus (such as durability in water and mutability) explains the diversity observed. Using a theoretical model, we show that the combination of the short lifespan of wild birds, and greater durability of viruses in aquatic environments, is key to maintaining the high levels of influenza diversity observed in wild birds.

Wild bird surveillance for avian influenza virus.

Avian influenza (AI) viruses have been isolated from a wide-diversity of free-living avian species representing several taxonomic orders. Isolations are most frequently reported from aquatic birds in the Orders Anseriformes and Charadriiformes, which are believed to be the primordial reservoirs for all AI viruses. Since first recognized in the late 1800s, AI viruses have been an important agent of disease in poultry and, occasionally, of non-gallinaceous birds and mammals. However, recent infections of humans with AI viruses, including highly pathogenic avian influenza (HPAI) H5N1 virus and low pathogenicity H7N9 AI virus in China during 2013, have increased the awareness of their potential to impact agricultural, wildlife, and public health. This chapter is intended to give general concepts and guidelines for planning and implementing surveillance programs for AI virus in wild birds.

PRESENCIA DEL VIRUS DE INFLUENZA AVIAR EN AVES SILVESTRES DE LOS HUMEDALES DE PUERTO VIEJO, LIMA

The objective of the study was to detect the presence of avian influenza (AI) virus in wild aquatic birds found in Puerto Viejo wetlands, Lima-Peru. Fresh faecal samples (n=900) from 18 species of wild birds were collected from April 2008 to February 2009. Samples were analyzed by virus isolation in SPF embryonated chicken eggs. Seven strains of low pathogenicity AI viruses subtype H12N5 were isolated; six from the migratory species Arenaria interpres, and one from the resident species Fulica ardesiaca. The technique of risk assessment using Monte Carlo Simulation (program @ risk) indicated that the probability of finding the AI virus in wild birds from Puerto Viejo wetlands was 0.88% with a confidence interval of 0.15 to 2.53%. The results of the study showed that wild birds from Puerto Viejo wetlands constitute a reservoir for avian influenza virus in Peru.

Complete Genome Sequence of an H9N2 Avian Influenza Virus Isolated from Egret in Lake Dongting Wetland

We isolated a recombinant H9N2 avian influenza virus (AIV) from fresh egret feces in the Ardeidae protection region of the Dongting Lake wetland area in China, and it was designated A/Egret/Hunan/1/2012(H9N2). This is the first report of isolating H9N2 AIV from wild birds in the Dongting Lake wetland. Its eight gene segments are generated by reassortment of gene segments of different AIV subtypes. These results are helpful for understanding the epidemiology and evolution of AIV in wild birds during migration.

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.

The consequences of climate change at an avian influenza 'hotspot'.

Avian influenza viruses (AIVs) pose significant danger to human health. A key step in managing this threat is understanding the maintenance of AIVs in wild birds, their natural reservoir. Ruddy turnstones (Arenaria interpres) are an atypical bird species in this regard, annually experiencing high AIV prevalence in only one location-Delaware Bay, USA, during their spring migration. While there, they congregate on beaches, attracted by the super-abundance of horseshoe crab eggs. A relationship between ruddy turnstone and horseshoe crab (Limulus polyphemus) population sizes has been established, with a declining horseshoe crab population linked to a corresponding drop in ruddy turnstone population sizes. The effect of this interaction on AIV prevalence in ruddy turnstones has also been addressed. Here, we employ a transmission model to investigate how the interaction between these two species is likely to be altered by climate change. We explore the consequences of this modified interaction on both ruddy turnstone population size and AIV prevalence and show that, if climate change leads to a large enough mismatch in species phenology, AIV prevalence in ruddy turnstones will increase even as their population size decreases.

Towards a new, ecologically targeted approach to monitoring wild bird populations for avian influenza viruses

Prevalence monitoring of avian influenza in wild bird populations is important to estimate risks for the occurrence of potentially zoonotic and economically disastrous outbreaks of highly pathogenic avian influenza virus (AIV) in poultry worldwide. A targeted, cost-effective monitoring method for AIV in wild birds was developed, which is based on monitoring results for AIV in Germany and information on the distribution and abundance of wild bird species in selected habitat types. Spatial data were combined with virological and outbreak data for the period of 1 January 2006 to 31 December 2010. Using Germany as an example, we identified 11 indicator species. By concentrating monitoring efforts on these species in spatially confined locations, we propose a targeted and more cost-effective risk-based AIV monitoring approach that can be adapted universally for the identification of wild bird indicator species worldwide with the perspective of reducing sample sizes (and costs) without impairing the validity of the results.

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.

Rapid diagnosis of avian influenza virus in wild birds: use of a portable rRT-PCR and freeze-dried reagents in the field.

Wild birds have been implicated in the spread of highly pathogenic avian influenza (HPAI) of the H5N1 subtype, prompting surveillance along migratory flyways. Sampling of wild birds for avian influenza virus (AIV) is often conducted in remote regions, but results are often delayed because of the need to transport samples to a laboratory equipped for molecular testing. Real-time reverse transcriptase polymerase chain reaction (rRT-PCR) is a molecular technique that offers one of the most accurate and sensitive methods for diagnosis of AIV. The previously strict lab protocols needed for rRT-PCR are now being adapted for the field. Development of freeze-dried (lyophilized) reagents that do not require cold chain, with sensitivity at the level of wet reagents has brought on-site remote testing to a practical goal. Here we present a method for the rapid diagnosis of AIV in wild birds using an rRT-PCR unit (Ruggedized Advanced Pathogen Identification Device or RAPID, Idaho Technologies, Salt Lake City, UT) that employs lyophilized reagents (Influenza A Target 1 Taqman; ASAY-ASY-0109, Idaho Technologies). The reagents contain all of the necessary components for testing at appropriate concentrations in a single tube: primers, probes, enzymes, buffers and internal positive controls, eliminating errors associated with improper storage or handling of wet reagents. The portable unit performs a screen for Influenza A by targeting the matrix gene and yields results in 2-3 hours. Genetic subtyping is also possible with H5 and H7 primer sets that target the hemagglutinin gene. The system is suitable for use on cloacal and oropharyngeal samples collected from wild birds, as demonstrated here on the migratory shorebird species, the western sandpiper (Calidrus mauri) captured in Northern California. Animal handling followed protocols approved by the Animal Care and Use Committee of the U.S. Geological Survey Western Ecological Research Center and permits of the U.S. Geological Survey Bird Banding Laboratory. The primary advantage of this technique is to expedite diagnosis of wild birds, increasing the chances of containing an outbreak in a remote location. On-site diagnosis would also prove useful for identifying and studying infected individuals in wild populations. The opportunity to collect information on host biology (immunological and physiological response to infection) and spatial ecology (migratory performance of infected birds) will provide insights into the extent to which wild birds can act as vectors for AIV over long distances.

Rapid Diagnosis of Avian Influenza Virus in Wild Birds: Use of a Portable rRT-PCR and Freeze-dried Reagents in the Field

Wild birds have been implicated in the spread of highly pathogenic avian influenza (HPAI) of the H5N1 subtype, prompting surveillance along migratory flyways. Sampling of wild birds for avian influenza virus (AIV) is often conducted in remote regions, but results are often delayed because of the need to transport samples to a laboratory equipped for molecular testing. Real-time reverse transcriptase polymerase chain reaction (rRT-PCR) is a molecular technique that offers one of the most accurate and sensitive methods for diagnosis of AIV. The previously strict lab protocols needed for rRT-PCR are now being adapted for the field. Development of freeze-dried (lyophilized) reagents that do not require cold chain, with sensitivity at the level of wet reagents has brought on-site remote testing to a practical goal. Here we present a method for the rapid diagnosis of AIV in wild birds using an rRT-PCR unit (Ruggedized Advanced Pathogen Identification Device or RAPID, Idaho Technologies, Salt Lake City, UT) that employs lyophilized reagents (Influenza A Target 1 Taqman; ASAY-ASY-0109, Idaho Technologies). The reagents contain all of the necessary components for testing at appropriate concentrations in a single tube: primers, probes, enzymes, buffers and internal positive controls, eliminating errors associated with improper storage or handling of wet reagents. The portable unit performs a screen for Influenza A by targeting the matrix gene and yields results in 2-3 hours. Genetic subtyping is also possible with H5 and H7 primer sets that target the hemagglutinin gene. The system is suitable for use on cloacal and oropharyngeal samples collected from wild birds, as demonstrated here on the migratory shorebird species, the western sandpiper (Calidrus mauri) captured in Northern California. Animal handling followed protocols approved by the Animal Care and Use Committee of the U.S. Geological Survey Western Ecological Research Center and permits of the U.S. Geological Survey Bird Banding Laboratory. The primary advantage of this technique is to expedite diagnosis of wild birds, increasing the chances of containing an outbreak in a remote location. On-site diagnosis would also prove useful for identifying and studying infected individuals in wild populations. The opportunity to collect information on host biology (immunological and physiological response to infection) and spatial ecology (migratory performance of infected birds) will provide insights into the extent to which wild birds can act as vectors for AIV over long distances.

Characterization of influenza A viruses isolated from wild waterfowl in Zambia

Although the quest to clarify the role of wild birds in the spread of the highly pathogenic H5N1 avian influenza virus (AIV) has yielded considerable data on AIVs in wild birds worldwide, information regarding the ecology and epidemiology of AIVs in African wild birds is still very limited. During AIV surveillance in Zambia (2008-2009), 12 viruses of distinct subtypes (H3N8, H4N6, H6N2, H9N1 and H11N9) were isolated from wild waterfowl. Phylogenetic analyses demonstrated that all the isolates were of the Eurasian lineage. Whilst some genes were closely related to those of AIVs isolated from wild and domestic birds in South Africa, intimating possible AIV exchange between wild birds and poultry in southern Africa, some gene segments were closely related to those of AIVs isolated in Europe and Asia, thus confirming the inter-regional AIV gene flow among these continents. Analysis of the deduced amino acid sequences of internal proteins revealed that several isolates harboured particular residues predominantly observed in human influenza viruses. Interestingly, the isolates with human-associated residues exhibited higher levels of virus replication in the lungs of infected mice and caused more morbidity as measured by weight loss than an isolate lacking such residues. This study stresses the need for continued monitoring of AIVs in wild and domestic birds in southern Africa to gain a better understanding of the emergence of strains with the potential to infect mammals.

Genetic Analysis of Avian Influenza Virus from Wild Birds and Mallards Reared for Shooting in Denmark

Denmark forms a geographical bottleneck along the migration route of many water birds breeding from northeastern Canada to north Siberia that gather to winter in Europe and Africa. Potentially, the concentration of such large numbers of water birds enhances the risk of avian influenza virus (AIV) introduction to domestic poultry. In 2003, Denmark initiated a nationwide survey of AIV in wild birds and mallards reared for shooting. Partial sequence analysis of the six internal genes from a total of 12 low pathogenic (LP) AIV isolates obtained in 2003 showed that genes from these viruses were closely related with genes from AIV circulating in northern Europe. For the Danish sequences only the PB2 and NS genes differ, so they cluster to more than one cluster in the phylogenetic trees. In spring 2006, highly pathogenic (HP) AIV H5N1 was detected in 44 cases of wild birds in Denmark. Sequence analysis of the HP H5N1 virus genome showed that it was not related to the LPAIV isolated previously, but closely related to the HPAIV H5 (Asian type) detected in the rest of Europe at that time. Even though only partial sequences were applied, this gave the idea for future full-length sequence studies.

Avian Influenza in North and South America, the Caribbean, and Australia, 2006–2008

Between 2006 and 2008, only one outbreak of highly pathogenic notifiable avian influenza (AI) was reported from the Americas, the Caribbean, and Australia. The outbreak, caused by H7N3, occurred in September 2007 in a multiage broiler breeder facility (approximately 49,000 birds) near Regina Beach in southern Saskatchewan, Canada. The disease was confined to a single farm; the farm was depopulated. All other reports of infections in poultry or wild birds involved low pathogenicity AI viruses. A notable event that occurred during the 3-yr period was the spread of low pathogenicity notifiable AI (LPNAI) H5N2 (Mexican lineage) into the Caribbean countries of the Dominican Republic and Haiti in 2007 and 2008, respectively, representing the first detection of AI reported in these countries. Mexico reported that the LPNAI H5N2 virus continued to circulate in the central regions of the country, and a total of 49 isolations were made from 12 states between 2006 and 2008. Also, during this period there was a significant increase in AI surveillance in many countries throughout the Americas, the Caribbean, and Australia, resulting in the detection of AI subtypes H1 through H12 and N1 through N9 in domestic bird species (chickens, turkeys, guinea fowl, upland game birds, and ducks/geese). The United States was the only one of these countries that reported detections of LPNAI (H5 or H7) infections in commercial poultry: one in chickens (H7N3, 2007), two in turkeys (H5N1 and H5N2, 2007), and one in pheasants (H5N8, 2008). Detections of AI viruses in wild birds between 2006 and 2008 were reported from North America (Canada and the United States), South America (Bolivia, Argentina, Chile, and Brazil), and Australia.

Characterization of low pathogenicity avian influenza viruses isolated from wild birds in Mongolia 2005 through 2007

BackgroundSince the emergence of H5N1 high pathogenicity (HP) avian influenza virus (AIV) in Asia, numerous efforts worldwide have focused on elucidating the relative roles of wild birds and domestic poultry movement in virus dissemination. In accordance with this a surveillance program for AIV in wild birds was conducted in Mongolia from 2005-2007. An important feature of Mongolia is that there is little domestic poultry production in the country, therefore AIV detection in wild birds would not likely be from spill-over from domestic poultry.ResultsDuring 2005-2007 2,139 specimens representing 4,077 individual birds of 45 species were tested for AIV by real time RT-PCR (rRT-PCR) and/or virus isolation. Bird age and health status were recorded. Ninety rRT-PCR AIV positive samples representing 89 individual birds of 19 species including 9 low pathogenicity (LP) AIVs were isolated from 6 species. A Bar-headed goose (Anser indicus), a Whooper swan (Cygnus cygnus) and 2 Ruddy shelducks (Tadorna ferruginea) were positive for H12N3 LP AIV. H16N3 and H13N6 viruses were isolated from Black-headed gulls (Larus ridibundus). A Red-crested pochard (Rhodonessa rufina) and 2 Mongolian gulls (Larus vagae mongolicus) were positive for H3N6 and H16N6 LP AIV, respectively. Full genomes of each virus isolate were sequenced and analyzed phylogenetically and were most closely related to recent European and Asian wild bird lineage AIVs and individual genes loosely grouped by year. Reassortment occurred within and among different years and subtypes.ConclusionDetection and/or isolation of AIV infection in numerous wild bird species, including 2 which have not been previously described as hosts, reinforces the wide host range of AIV within avian species. Reassortment complexity within the genomes indicate the introduction of new AIV strains into wild bird populations annually, however there is enough over-lap of infection for reassortment to occur. Further work is needed to clarify how AIV is maintained in these wild bird reservoirs.

The ecology of avian influenza virus in wild birds: What does this mean for poultry?

As natural hosts for avian influenza virus (AIV), wild birds, particularly aquatic birds, are the primary reservoir for transmission of AIV to domestic poultry. Therefore, understanding the dissemination and maintenance of AIV in wild birds is important for understanding the factors that contribute to transmission of AIV from wild birds to poultry. However, relatively little is known about the ecology of the virus in wild birds, and the depth of data are inconsistent worldwide. Also, the biology of the virus itself is very important, because AIV is highly adaptable to different hosts and likely to the environment as well. Some insight may be gained from the Asian H5N1 highly pathogenic AIV lineage, because surveillance for this virus has increased considerably in wild birds worldwide since 2005. Also, numerous species that have not previously been represented in AIV testing have been included in surveillance for the Asian H5N1 highly pathogenic AIV, allowing for a more complete understanding of the distribution of AIV in wild birds.