No evidence for homosubtypic immunity of influenza H3 in Mallards following vaccination in a natural experimental system.

The Mallard (Anas platyrhynchos) is an important reservoir species for influenza A viruses (IAV), and in this host, prevalence and virus diversity are high. Studies have demonstrated the presence of homosubtypic immunity, where individuals are unlikely to be reinfected with the same subtype within an autumn season. Further, evidence for heterosubtypic immunity exists, whereby immune responses specific for one subtype offer partial or complete protection against related HA subtypes. We utilized a natural experimental system to determine whether homo- or heterospecific immunity could be induced following experimental vaccination. Thirty Mallards were vaccinated with an inactivated H3, H6 or a sham vaccine and after seroconversion were exposed to naturally infected wild conspecifics. All ducks were infected within 2 days and had both primary and secondary infections. Overall, there was no observable difference between groups; all individuals were infected with H3 and H10 IAV. At the cessation of the experiment, most individuals had anti-NP antibodies and neutralizing antibodies against H10. Not all individuals had H3 neutralizing antibodies. The isolated H3 IAVs revealed genetic dissimilarity to the H3 vaccine strain, specifically substitutions in the vicinity of the receptor-binding site. There was no evidence of vaccine-induced homosubtypic immunity to H3, a likely result of both a poor H3 immune response in the ducks and H3 immune escape. Likewise, there was no observed heterosubtypic protection related to H6 vaccination. This study highlights the need for experimental approaches to assess how exposure to pathogens and resulting immune processes translates to individual and population disease dynamics.

Pathogenesis of Vesicular Stomatitis New Jersey Virus Infection in Deer Mice ( Peromyscus maniculatus) Transmitted by Black Flies ( Simulium vittatum).

The natural transmission of vesicular stomatitis New Jersey virus (VSNJV), an arthropod-borne virus, is not completely understood. Rodents may have a role as reservoir or amplifying hosts. In this study, juvenile and nestling deer mice ( Peromyscus maniculatus) were exposed to VSNJV-infected black fly ( Simulium vittatum) bites followed by a second exposure to naive black flies on the nestling mice. Severe neurological signs were observed in some juvenile mice by 6 to 8 days postinoculation (DPI); viremia was not detected in 25 juvenile deer mice following exposure to VSNJV-infected fly bites. Both juvenile and nestling mice had lesions and viral antigen in the central nervous system (CNS); in juveniles, their distribution suggested that the sensory pathway was the most likely route to the CNS. In contrast, a hematogenous route was probably involved in nestling mice, since all of these mice developed viremia and had widespread antigen distribution in the CNS and other tissues on 2 DPI. VSNJV was recovered from naive flies that fed on viremic nestling mice. This is the first report of viremia in a potential natural host following infection with VSNJV via insect bite and conversely of an insect becoming infected with VSNJV by feeding on a viremic host. These results, along with histopathology and immunohistochemistry, show that nestling mice have widespread dissemination of VSNJV following VSNJV-infected black fly bite and are a potential reservoir or amplifying host for VSNJV.

Environmental Stability of Swine and Human Pandemic Influenza Viruses in Water under Variable Conditions of Temperature, Salinity, and pH.

UNLABELLED: The movement of influenza A viruses (IAVs) from wild bird reservoirs to domestic animals and humans is well established, but the transmission mechanisms that facilitate efficient movement across and within these host populations are not fully defined. Although predominant routes of transmission vary between host populations, the extent of environmental stability needed for efficient IAV transmission also may vary. Because of this, we hypothesized that virus stability would differ in response to varied host-related transmission mechanisms; if correct, such phenotypic variation might represent a potential marker for the emergence of novel animal or human influenza viruses. Here, the objective was to evaluate the ability of eight swine and six human IAV isolates to remain infective under various pH, temperature, and salinity conditions using a preestablished distilled water system. Swine and human viruses persisted longest at near-neutral pH, at cold temperatures, or under "freshwater" conditions. Additionally, no significant differences in persistence were observed between pandemic and nonpandemic IAVs. Our results indicate that there have been no apparent changes in the environmental stability of the viruses related to host adaptation. IMPORTANCE: This study assessed the environmental stability of eight swine and six human influenza A viruses (IAVs), including viruses associated with the 2009 H1N1 pandemic, in a distilled water system. The important findings of this work are that IAV persistence can be affected by environmental variables and that no marked changes were noted between human and swine IAVs or between pandemic and nonpandemic IAVs.

Molecular evolution of epizootic hemorrhagic disease viruses in North America based on historical isolates using motif fingerprints.

Epizootic hemorrhagic disease virus (EHDV) is an orbivirus of the Reoviridae family that has significant impact on wild and captive white-tailed deer. Although closely related to bluetongue virus that can cause disease in sheep and cattle, North American EHDV historically has not been associated with disease in cattle or sheep. Severe disease in cattle has been reported with other EHDV strains from East Asia and the Middle East. To understand the potential role of viral genetics in the epidemiology of epizootic hemorrhagic disease, a molecular characterization of North American EHDV strains from 1955 to 2012 was conducted via conventional phylogenetic analysis and a new classification approach using motif fingerprint patterns. Overall, this study indicates that the genetic make-up of EHDV populations in North America have slowly evolved over time. The data also suggested limited reassortment events between serotypes 1 and 2 and introduces a new analysis tool for more detailed sequence pattern analysis.

Host and Potential Vector Susceptibility to an Emerging Orbivirus in the United States: Epizootic Hemorrhagic Disease Virus Serotype 6.

Epizootic hemorrhagic disease viruses (EHDVs) are orbiviruses transmitted by Culicoides biting midges to domestic and wild ruminants. EHDV-1 and EHDV-2 are endemic in the United States, where epizootic hemorrhagic disease is the most significant viral disease of white-tailed deer (WTD;Odocoileus virginianus) and reports of epizootic hemorrhagic disease in cattle are increasing. In 2006, a reassortant EHDV-6 was isolated from dead WTD in Indiana and has been detected each subsequent year over a wide geographic region. Since EHDV-6 is not a historically endemic serotype in the United States, it is important to understand infection outcome in potential hosts. Specifically, we aimed to evaluate the pathogenicity of the virus in 2 primary US ruminant hosts (WTD and cattle) and the susceptibility of a confirmed US vector (Culicoides sonorensis). Five WTD and 4 cattle were inoculated with >10(6)TCID50EHDV-6 by intradermal and subcutaneous injection. All 5 WTD exhibited moderate to severe disease, and 3 died. Viremia was first detected 3 to 5 days postinfection (dpi) with surviving animals seroconverting by 10 dpi. Two of 4 inoculated cattle had detectable viremia, 5 to 10 dpi and 7 to 24 dpi, respectively. No clinical, hematologic, or pathologic abnormalities were observed. Antibodies were detected by 10 dpi in 3 of 4 cows.C. sonorensis were fed on WTD blood spiked with EHDV-6 and held for 4 to 14 days postfeeding at 25°C. From 4 to 14 days postfeeding, 19 of 171 midges were virus isolation positive and 6 of 171 had ≥10(2.7)TCID50EHDV-6. Although outcomes varied, these studies demonstrate the susceptibility of ruminant and vector hosts in the United States for this recently emerged EHDV serotype.

Evolutionary dynamics of West Nile virus in Georgia, 2001-2011.

From 1999-2001, West Nile virus (WNV) spread throughout the eastern United States (US) and was first detected in Georgia in 2001. To date, the virus has been detected in over 2,500 dead wild bird and mosquito samples from across Georgia. We sequenced the premembrane (preM) and envelope gene (E) (2004 bp) from 111 isolates collected from 2001 to 2011. To assess viral gene flow from other geographic regions in the US, we combined our data with WNV sequences available at the National Center for Biotechnology Information (NCBI) and performed phylogenetic analysis. We found evidence that WNV isolates detected in Chatham County Georgia most likely originated from the Northeastern United States. These results highlight the growing importance of adequate genetic surveillance for monitoring and controlling viruses of public health concern.

Co-infection of mallards with low-virulence Newcastle disease virus and low-pathogenic avian influenza virus.

Waterfowl are considered the natural reservoir of low-virulence Newcastle disease viruses (loNDVs) and low-pathogenic avian influenza viruses (LPAIVs). The objective of this study was to investigate the effect of co-infections with loNDV and LPAIV on the infectivity and excretion of these viruses in mallards. One-month-old mallards were inoculated intranasally with 10(6) median embryo infectious doses of a wild-bird-origin loNDV and A/Mallard/MN/199106/99 (H3N8) LPAIV on the same day or received the LPAIV 2 or 5 days after loNDV inoculation. All mallards became infected with both viruses based on detection of seroconversion and viral shedding. Co-infection resulted in a higher number of cloacal swabs detected positive for LPAIV and a lower number of cloacal swabs detected positive for loNDV in some groups, although differences between groups were not statistically significant. Co-infection did not affect replication of LPAIV in epithelial cells of the lower intestine and bursa of Fabricius. In summary, the results of this study indicate that co-infection with LPAIV and loNDV does not affect the ability of mallards to be infected with either virus although it may have minimal effects on patterns (source and timing) of viral shedding.

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.

Expression and distribution of sialic acid influenza virus receptors in wild birds.

Avian influenza (AI) viruses have been detected in more than 105 wild bird species from 12 different orders but species-related differences in susceptibility to AI viruses exist. Expression of α2,3-linked (avian-type) and α2,6-linked (human-type) sialic acid (SA) influenza virus receptors in tissues is considered one of the determinants of the host range and tissue tropism of influenza viruses. We investigated the expression of these SA receptors in 37 wild bird species from 11 different orders by lectin histochemistry. Two isoforms of Maackia amurensis (MAA) lectin, MAA1 and MAA2, were used to detect α2,3-linked SA, and Sambucus nigra lectin was used to detect α2,6-linked SA. All species evaluated expressed α2,3-linked and α2,6-linked SA receptors in endothelial cells and renal tubular epithelial cells. Both α2,3-linked and α-2,6-linked SA receptors were expressed in respiratory and intestinal tract tissues of aquatic and terrestrial wild bird species from different taxa, but differences in SA expression and in the predominant isoform of MAA lectin bound were observed. With a few possible exceptions, these observed differences were not generally predictive of reported species susceptibility to AI viruses based on published experimental and field data.

Domestic cats are susceptible to infection with low pathogenic avian influenza viruses from shorebirds.

Domestic cats are susceptible to infection with highly pathogenic avian influenza virus H5N1, resulting in pneumonia and in some cases, systemic spread with lesions in multiple organ systems. Recent transmission of the 2009 pandemic H1N1 influenza virus from humans to cats also resulted in severe pneumonia in cats. Data regarding the susceptibility of cats to other influenza viruses is minimal, especially regarding susceptibility to low pathogenic avian influenza viruses from wild birds, the reservoir host. In this study, the authors infected 5-month-old cats using 2 different North American shorebird avian influenza viruses (H1N9 and H6N4 subtypes), 3 cats per virus, with the goal of expanding the understanding of avian influenza virus infections in this species. These viruses replicated in inoculated cats based on virus isolation from the pharynx in 2 cats, virus isolation from the lung of 1 cat, and antigen presence in the lung via immunohistochemistry in 2 cats. There was also seroconversion and lesions of patchy bronchointerstitial pneumonia in all of the cats. Infection in the cats did not result in clinical disease and led to variable pharyngeal viral shedding with only 1 of the viruses; virus was localized in the alveolar epithelium via immunohistochemistry. These findings demonstrate the capacity of wild bird influenza viruses to infect cats, and further investigation is warranted into the pathogenesis of these viruses in cats from both a veterinary medical and public health perspective.

Experimental infection of bar-headed geese (Anser indicus) and ruddy shelducks (Tadorna ferruginea) with a clade 2.3.2 H5N1 highly pathogenic avian influenza virus.

Since 2005, clade 2.2 H5N1 highly pathogenic avian influenza (HPAI) viruses have caused infections and morbidity among numerous species of wild waterfowl in Eurasia and Africa. However, outbreaks associated with clade 2.3.2 viruses have increased since 2009, and viruses within this clade have become the dominant strain of the H5N1 HPAI virus detected in wild birds, reaching endemic status in domestic birds in select regions of Asia. To address questions regarding the emergence and expansion of clade 2.3.2 viruses, 2 waterfowl species repeatedly involved in outbreaks of H5N1 HPAI viruses, bar-headed geese (Anser indicus) and ruddy shelducks (Tadorna ferruginea), were inoculated with a representative virus. All of 3 infected ruddy shelducks exhibited neurologic signs and died within 4 to 5 days. Two of 3 infected bar-headed geese had transient weakness but all survived. Viral shedding was predominately via the oropharynx and was detected from 1 to 7 days after inoculation. The severity and distribution of microscopic lesions corresponded with clinical disease and influenza-specific immunohistochemical staining of neurons. The predominant lesions were in the brain and were more severe in ruddy shelducks. Increased caspase-3 reactivity in the brains of all infected birds suggests a role for apoptosis in H5N1 HPAI virus pathogenesis in these species. These results demonstrate that similar to clade 2.2 viruses, a clade 2.3.2 H5N1 HPAI virus is neurotropic in some waterfowl species and can lead to neurologic disease with varying clinical outcomes. This has implications for the role that wild waterfowl may play in transmission of this virus in endemic regions.

The pathogenesis of low pathogenic avian influenza in mallards.

Mallards are important natural hosts involved in the epidemiology of low pathogenic avian influenza viruses (LPAIVs). LPAIVs are mainly transmitted by a fecal-oral route and are excreted in high concentrations in the feces. We investigated the pathology, viral antigen distribution, and the expression of alpha2,3 sialic acid (SA) influenza virus receptors in mallards after intranasal inoculation with A/Mallard/MN/199106/99 (H3N8) or A/Mallard/MN/355779/00 (H5N2). Gross lesions were not observed. Avian influenza virus (AIV) nucleoprotein (NP) antigen was detected in rare epithelial cells of the larynx and trachea only at 1-day postinoculation (dpi) in the birds infected with H3N8 LPAIV, but infection with either virus was associated with lymphocytic tracheitis and laryngitis on 1 and 2 dpi. AIV NP antigen was detected in enterocytes of the lower intestine from 1 to 4 dpi and in epithelial cells of the bursa of Fabricius from 2 to 3 dpi in birds infected with either virus. Oropharyngeal and cloacal viral shedding was detected from 1 dpi, with higher cloacal viral shedding detected at 2 and 3 dpi with both viruses. Mallards abundantly expressed alpha2,3 sialic acid receptors in epithelial cells of the respiratory tract, lower intestine, and bursa of Fabricius. Some infected birds had decreased alpha2,3 sialic acid expression in epithelial cells of the bursa of Fabricius and in enterocytes of the ceca and colon. In conclusion, the main sites of LPAIV replication in mallards are the enterocytes of the lower intestinal tract and epithelial cells of the bursa of Fabricius in the first days after infection, when these birds are shedding AIV in high titers in the feces.

Detection of a novel reassortant epizootic hemorrhagic disease virus (EHDV) in the USA containing RNA segments derived from both exotic (EHDV-6) and endemic (EHDV-2) serotypes.

Epizootic hemorrhagic disease virus (EHDV) is a Culicoides-transmitted orbivirus that infects domestic and wild ruminants and is provisionally thought to be distributed throughout Africa, North America, Australia, East Asia and the Middle East. Historically, of the seven proposed serotypes of EHDV, only EHDV-1 and EHDV-2 have been reported from North America. In 2006, EHDV isolates were recovered from moribund or dead white-tailed deer (Odocoileus virginianus) in Indiana and Illinois that could not be identified as either EHDV-1 or EHDV-2 by virus neutralization tests or by serotype-specific RT-PCR. Additional serological and genetic testing identified the isolates as EHDV-6, a serotype that, although originally described from Australia, has recently been recognized as an emerging pathogen of cattle in Morocco, Algeria and Turkey. In 2007 and 2008, EHDV-6 was isolated again from white-tailed deer, this time in Missouri, Kansas and Texas, suggesting that the virus is capable of overwintering and that it may become, or already is, endemic in a geographically widespread region of the USA. Genetic characterization of the virus indicates that it is a reassortant, such that the outer capsid proteins determining serotype specificity (VP2 and VP5) are derived from exotic EHDV-6, whilst the remaining structural and non-structural proteins are apparently obtained from indigenous EHDV-2 (Alberta).

The effect of age on avian influenza viral shedding in mallards (Anas platyrhynchos).

Avian influenza virus (AIV) prevalence in wild aquatic bird populations varies with season, geographic location, host species, and age. It is not clear how age at infection affects the extent of viral shedding. To better understand the influence of age at infection on viral shedding of wild bird-origin low pathogenicity avian influenza (LPAI) viruses, mallards (Anas platyrhynchos) of increasing age (2 wk, 1 mo, 2 mo, 3 mo, and 4 mo) were experimentally inoculated via choanal cleft with a 10(6) median embryo infectious dose (EID50) of either A/Mallard/MN/355779/00 (H5N2) or A/Mallard/MN/199106/99 (H3N8). Exposed birds in all five age groups were infected by both AIV isolates and excreted virus via the oropharynx and cloaca. The 1-month and older groups consistently shed virus from 1 to 4 d post inoculation (dpi), whereas, viral shedding was delayed by 1 d in the 2-wk-old group. Past 4 dpi, viral shedding in all groups varied between individual birds, but virus was isolated from some birds in each group up to 21 dpi when the trial was terminated. The 1-mo-old group had the most productive shedding with a higher number of cloacal swabs that tested positive for virus over the study period and lower cycle threshold values on real-time reverse-transcription PCR. The viral shedding pattern observed in this study suggests that, although mallards from different age groups can become infected and shed LPAI viruses, age at time of infection might have an effect on the extent of viral shedding and thereby impact transmission of LPAI viruses within the wild bird reservoir system. This information may help us better understand the natural history of these viruses, interpret field and experimental data, and plan future experimental trials.

Tenacity of avian influenza viruses.

The goal of this review is to provide an overview of existing research on the environmental tenacity of avian influenza (AI) viruses, to identify gaps in our current understanding, and discuss how this information relates to AI control, eradication, and prevention. We are just beginning to understand the environmental factors that affect infectivity and the extent of variation in environmental tenacity that is present among these viruses. Because the environment can provide a bridge for AI virus transmission between many diverse hosts, including wild and domestic animals and man, understanding the importance of environmental transmission and identifying important points of contact are critical steps in preventing the spread of infection especially related to the introduction of these viruses to new host species.

Impediments to wildlife disease surveillance, research, and diagnostics.

There is a recognized need for increased wildlife disease surveillance and research related to understanding the epidemiology and control of emerging wildlife and zoonotic diseases. Although both passive and active surveillance strategies can and have been effectively used with wildlife, some unique problems are often encountered. These can include limitations related to case acquisition and under-reporting, difficulty in designing sampling strategies that adequately represent the population of interest, the lack of properly validated diagnostic tests, problems related to data interpretation due to missing or inaccurate denominator data, and the lack of an existing wildlife surveillance infrastructure. Many of these same problems are often encountered in field research, which can be further complicated by the complexity and scale of the natural systems in which this work takes place. Although such studies may be difficult, there are numerous examples of success and our understanding of wildlife and wildlife-related zoonotic and emerging disease continues to grow.

Evidence of avian metapneumovirus subtype C infection of wild birds in Georgia, South Carolina, Arkansas and Ohio, USA.

Metapneumoviruses (MPVs) were first reported in avian species (aMPVs) in the late 1970s and in humans in 2001. Although aMPVs have been reported in Europe and Asia for over 20 years, the virus first appeared in the United States in 1996, leaving many to question the origin of the virus and why it proved to be a different subtype from those found elsewhere. To examine the potential role of migratory waterfowl and other wild birds in aMPV spread, our study focused on determining whether populations of wild birds have evidence of aMPV infection. Serum samples from multiple species were initially screened using a blocking enzyme-linked immunosorbent assay. Antibodies to aMPVs were identified in five of the 15 species tested: American coots, American crows, Canada geese, cattle egrets, and rock pigeons. The presence of aMPV-specific antibodies was confirmed with virus neutralization and western blot assays. Oral swabs were collected from wild bird species with the highest percentage of aMPV-seropositive serum samples: the American coots and Canada geese. From these swabs, 17 aMPV-positive samples were identified, 11 from coots and six from geese. Sequence analysis of the matrix, attachment gene and short hydrophobic genes revealed that these viruses belong to subtype C aMPV. The detection of aMPV antibodies and the presence of virus in wild birds in Georgia, South Carolina, Arkansas and Ohio demonstrates that wild birds can serve as a reservoir of subtype C aMPV, and may provide a potential mechanism to spread aMPVs to poultry in other regions of the United States and possibly to other countries in Central and South America.

Is the occurrence of avian influenza virus in Charadriiformes species and location dependent?

Birds in the order Charadriiformes were sampled at multiple sites in the eastern half of the continental USA, as well as at Argentina, Chile, and Bermuda, during 1999-2005, and tested for avian influenza virus (AIV). Of more than 9,400 birds sampled, AIV virus was isolated from 290 birds. Although Ruddy Turnstones (Arenaria interpres) comprised just 25% of birds sampled, they accounted for 87% of isolates. Only eight AIV isolations were made from birds at four locations outside of the Delaware Bay, USA, region; six of these were from gulls (Laridae). At Delaware Bay, AIV isolations were predominated by hemagglutinin (HA) subtype H10, but subtype diversity varied each year. These results suggest that AIV infection among shorebirds (Scolopacidae) may be localized, species specific, and highly variable in relation to AIV subtype diversity.

White-tailed deer (Odocoileus virginianus) develop spirochetemia following experimental infection with Borrelia lonestari.

Borrelia lonestari is considered a putative agent of southern tick-associated rash illness (STARI) and is known to occur naturally only in lone star ticks (Amblyomma americanum) and white-tailed deer (Odocoileus virginianus). We used a low passage isolate of B. lonestari (LS-1) to inoculate white-tailed deer, C3H mice, Holstein cattle, and beagles. Animals were monitored via examination of Giemsa and acridine orange stained blood smears, polymerase chain reaction (PCR), indirect fluorescent antibody (IFA) test, and/or culture isolation. Spirochetes were visualized in blood smears of both deer on days post-inoculation (DPI) 6, 8, 12 and one deer on DPI 15. Whole blood collected from deer tested PCR positive starting on DPI 4 and remained positive as long as DPI 28. Both deer developed antibody titers of >64, with a maximum IFA titer of 1024. The organism was reisolated from the blood of both deer on DPI 6 and one deer on DPI 12. All isolation attempts from mice, calves, or dogs were negative, although one of seven mice was transiently PCR positive. Mice and dogs developed an IFA titer > or =64, while calves lacked a detectable antibody response. These preliminary experimental infection trials show that white-tailed deer are susceptible to infection with B. lonestari and develop a spirochetemia following needle-inoculation, while C3H mice, calves, and dogs do not. Results suggest that deer may serve as a vertebrate reservoir host. Tick transmission studies are needed to confirm that this organism can be maintained in a natural cycle involving deer and A. americanum.

Optimizing Surveillance for South American Origin Influenza A Viruses Along the United States Gulf Coast Through Genomic Characterization of Isolates from Blue-winged Teal (Anas discors).

Relative to research focused on inter-continental viral exchange between Eurasia and North America, less attention has been directed towards understanding the redistribution of influenza A viruses (IAVs) by wild birds between North America and South America. In this study, we genomically characterized 45 viruses isolated from blue-winged teal (Anas discors) along the Texas and Louisiana Gulf Coast during March of 2012 and 2013, coincident with northward migration of this species from Neotropical wintering areas to breeding grounds in the United States and Canada. No evidence of South American lineage genes was detected in IAVs isolated from blue-winged teal supporting restricted viral gene flow between the United States and southern South America. However, it is plausible that blue-winged teal redistribute IAVs between North American breeding grounds and wintering areas throughout the Neotropics, including northern South America, and that viral gene flow is limited by geographical barriers further south (e.g., the Amazon Basin). Surveillance for the introduction of IAVs from Central America and northern South America into the United States may be further optimized through genomic characterization of viruses resulting from coordinated, concurrent sampling efforts targeting blue-winged teal and sympatric species throughout the Neotropics and along the United States Gulf Coast.