Continental-scale dynamics of avian influenza in U.S. waterfowl are driven by demography, migration, and temperature.

Emerging diseases of wildlife origin are increasingly spilling over into humans and domestic animals. Surveillance and risk assessments for transmission between these populations are informed by a mechanistic understanding of the pathogens in wildlife reservoirs. For avian influenza viruses (AIV), much observational and experimental work in wildlife has been conducted at local scales, yet fully understanding their spread and distribution requires assessing the mechanisms acting at both local, (e.g., intrinsic epidemic dynamics), and continental scales, (e.g., long-distance migration). Here, we combined a large, continental-scale data set on low pathogenic, Type A AIV in the United States with a novel network-based application of bird banding/recovery data to investigate the migration-based drivers of AIV and their relative importance compared to well-characterized local drivers (e.g., demography, environmental persistence). We compared among regression models reflecting hypothesized ecological processes and evaluated their ability to predict AIV in space and time using within and out-of-sample validation. We found that predictors of AIV were associated with multiple mechanisms at local and continental scales. Hypotheses characterizing local epidemic dynamics were strongly supported, with age, the age-specific aggregation of migratory birds in an area and temperature being the best predictors of infection. Hypotheses defining larger, network-based features of the migration processes, such as clustering or between-cluster mixing explained less variation but were also supported. Therefore, our results support a role for local processes in driving the continental distribution of AIV.

Loci Associated With Antibody Response in Feral Swine (Sus scrofa) Infected With Brucella suis.

Feral swine (Sus scrofa) are a destructive invasive species widespread throughout the United States that disrupt ecosystems, damage crops, and carry pathogens of concern for the health of domestic stock and humans including Brucella suis-the causative organism for swine brucellosis. In domestic swine, brucellosis results in reproductive failure due to abortions and infertility. Contact with infected feral swine poses spillover risks to domestic pigs as well as humans, companion animals, wildlife, and other livestock. Genetic factors influence the outcome of infectious diseases; therefore, genome wide association studies (GWAS) of differential immune responses among feral swine can provide an understanding of disease dynamics and inform management to prevent the spillover of brucellosis from feral swine to domestic pigs. We sought to identify loci associated with differential antibody responses among feral swine naturally infected with B. suis using a case-control GWAS. Tissue, serum, and genotype data (68,516 bi-allelic single nucleotide polymorphisms) collected from 47 feral swine were analyzed in this study. The 47 feral swine were culture positive for Brucella spp. Of these 47, 16 were antibody positive (cases) whereas 31 were antibody negative (controls). Single-locus GWAS were performed using efficient mixed-model association eXpedited (EMMAX) methodology with three genetic models: additive, dominant, and recessive. Eight loci associated with seroconversion were identified on chromosome 4, 8, 9, 10, 12, and 18. Subsequent bioinformatic analyses revealed nine putative candidate genes related to immune function, most notably phagocytosis and induction of an inflammatory response. Identified loci and putative candidate genes may play an important role in host immune responses to B. suis infection, characterized by a detectable bacterial presence yet a differential antibody response. Given that antibody tests are used to evaluate brucellosis infection in domestic pigs and for disease surveillance in invasive feral swine, additional studies are needed to fully understand the genetic component of the response to B. suis infection and to more effectively translate estimates of Brucella spp. antibody prevalence among feral swine to disease control management action.

Inferring seasonal infection risk at population and regional scales from serology samples.

Accurate estimates of seasonal infection risk can be used by animal health officials to predict future disease risk and improve understanding of the mechanisms driving disease dynamics. It can be difficult to estimate seasonal infection risk in wildlife disease systems because surveillance assays typically target antibodies (serosurveillance), which are not necessarily indicative of current infection, and serosurveillance sampling is often opportunistic. Recently developed methods estimate past time of infection from serosurveillance data using quantitative serological assays that indicate the amount of antibodies in a serology sample. However, current methods do not account for common opportunistic and uneven sampling associated with serosurveillance data. We extended the framework of survival analysis to improve estimates of seasonal infection risk from serosurveillance data across population and regional scales. We found that accounting for the right-censored nature of quantitative serology samples greatly improved estimates of seasonal infection risk, even when sampling was uneven in time. Survival analysis can also be used to account for common challenges when estimating infection risk from serology data, such as biases induced by host demography and continually elevated antibodies following infection. The framework developed herein is widely applicable for estimating seasonal infection risk from serosurveillance data in humans, wildlife, and livestock.

Detection error influences both temporal seroprevalence predictions and risk factors associations in wildlife disease models.

Understanding the prevalence of pathogens in invasive species is essential to guide efforts to prevent transmission to agricultural animals, wildlife, and humans. Pathogen prevalence can be difficult to estimate for wild species due to imperfect sampling and testing (pathogens may not be detected in infected individuals and erroneously detected in individuals that are not infected). The invasive wild pig (Sus scrofa, also referred to as wild boar and feral swine) is one of the most widespread hosts of domestic animal and human pathogens in North America.We developed hierarchical Bayesian models that account for imperfect detection to estimate the seroprevalence of five pathogens (porcine reproductive and respiratory syndrome virus, pseudorabies virus, Influenza A virus in swine, Hepatitis E virus, and Brucella spp.) in wild pigs in the United States using a dataset of over 50,000 samples across nine years. To assess the effect of incorporating detection error in models, we also evaluated models that ignored detection error. Both sets of models included effects of demographic parameters on seroprevalence. We compared our predictions of seroprevalence to 40 published studies, only one of which accounted for imperfect detection.We found a range of seroprevalence among the pathogens with a high seroprevalence of pseudorabies virus, indicating significant risk to livestock and wildlife. Demographics had mostly weak effects, indicating that other variables may have greater effects in predicting seroprevalence.Models that ignored detection error led to different predictions of seroprevalence as well as different inferences on the effects of demographic parameters.Our results highlight the importance of incorporating detection error in models of seroprevalence and demonstrate that ignoring such error may lead to erroneous conclusions about the risk associated with pathogen transmission. When using opportunistic sampling data to model seroprevalence and evaluate risk factors, detection error should be included.

Individual-Level Antibody Dynamics Reveal Potential Drivers of Influenza A Seasonality in Wild Pig Populations.

Swine are important in the ecology of influenza A virus (IAV) globally. Understanding the ecological role of wild pigs in IAV ecology has been limited because surveillance in wild pigs is often for antibodies (serosurveillance) rather than IAVs, as in humans and domestic swine. As IAV antibodies can persist long after an infection, serosurveillance data are not necessarily indicative of current infection risk. However, antibody responses to IAV infections cause a predictable antibody response, thus time of infection can be inferred from antibody levels in serological samples, enabling identification of risk factors of infection at estimated times of infection. Recent work demonstrates that these quantitative antibody methods (QAMs) can accurately recover infection dates, even when individual-level variation in antibody curves is moderately high. Also, the methodology can be implemented in a survival analysis (SA) framework to reduce bias from opportunistic sampling. Here we integrated QAMs and SA and applied this novel QAM-SA framework to understand the dynamics of IAV infection risk in wild pigs seasonally and spatially, and identify risk factors. We used national-scale IAV serosurveillance data from 15 US states. We found that infection risk was highest during January-March (54% of 61 estimated peaks), with 24% of estimated peaks occurring from May to July, and some low-level of infection risk occurring year-round. Time-varying IAV infection risk in wild pigs was positively correlated with humidity and IAV infection trends in domestic swine and humans, and did not show wave-like spatial spread of infection among states, nor more similar levels of infection risk among states with more similar meteorological conditions. Effects of host sex on IAV infection risk in wild pigs were generally not significant. Because most of the variation in infection risk was explained by state-level factors or infection risk at long-distances, our results suggested that predicting IAV infection risk in wild pigs is complicated by local ecological factors and potentially long-distance translocation of infection. In addition to revealing factors of IAV infection risk in wild pigs, our framework is broadly applicable for quantifying risk factors of disease transmission using opportunistic serosurveillance sampling, a common methodology in wildlife disease surveillance. Future research on the factors that determine individual-level antibody kinetics will facilitate the design of serosurveillance systems that can extract more accurate estimates of time-varying disease risk from quantitative antibody data.

RACCOON (PROCYON LOTOR) RESPONSE TO ONTARIO RABIES VACCINE BAITS (ONRAB) IN ST. LAWRENCE COUNTY, NEW YORK, USA.

Oral rabies vaccination (ORV) campaigns have been conducted annually in the US over the past two decades to prevent raccoon (Procyon lotor) rabies, which is enzootic along the eastern region of the country from southeastern Canada to Alabama. Because raccoon rabies has been eliminated from neighboring Canadian provinces, continued detection of the variant in the US is of concern due to the potential for infected raccoons to cross the border via the St. Lawrence River. Ontario Rabies Vaccine Baits (ONRAB) containing a live, recombinant human adenovirus expressing the rabies virus glycoprotein have been under experimental use in the US since 2011. We distributed ONRAB in St. Lawrence County, New York, from 2013 to 2015 as part of field trials to evaluate serologic responses in raccoons. Prior to ONRAB distribution, rabies virus neutralizing antibody (RVNA) seroprevalence in raccoons was 45.2% (183 of 405) and increased to 57.7% (165 of 286) after 3 yr of ONRAB baiting. Postbait RVNA seroprevalence increased each year, with a lower response observed in juvenile compared with adult raccoons. The pre-ONRAB seroprevalence detected in 2013 was relatively high and was likely impacted both by elevated rabies activity in the county and the use of ORV with a different vaccine bait for 14 consecutive years prior to our study. Tetracycline biomarker prevalence increased from 1.4% prior to ONRAB baiting to 51.3% from 2013 to 2015, demonstrating bait palatability to raccoons. These data complemented related field trials conducted in West Virginia and the northeastern US.

EFFECT OF HIGH-DENSITY ORAL RABIES VACCINE BAITING ON RABIES VIRUS NEUTRALIZING ANTIBODY RESPONSE IN RACCOONS ( PROCYON LOTOR).

From 2014 to 2016, we examined the effect of distributing oral rabies vaccine baits at high density (150 baits/km2) in an area of Virginia, US that was naïve to oral rabies vaccination prior to the study. We also compared the effect of baiting at high density in a naïve area to baiting at standard density (75 baits/km2) in an area that had been baited annually for 12 yr. Our results suggested that rabies virus seroconversion in raccoons ( Procyon lotor) gradually increased each year under the highdensity bait treatment. However, we did not detect a difference in seroconversion between bait density treatments. Virginia opossums ( Didelphis virginiana) were abundant in the study area and were a potentially important nontarget species that competed for oral rabies vaccine baits, but the ratio of opossums to raccoons in this study did not affect rabies virus neutralizing antibody response of the raccoon populations.

Pseudorabies detected in hunting dogs in Alabama and Arkansas after close contact with feral swine (Sus scrofa).

BACKGROUND: Pigs (Sus scrofa) are the natural hosts of pseudorabies virus (PRV), also known as Aujeszky's disease. Infection in mammals, with the exception of humans, typically causes extreme itching, facial swelling, and excessive salivation, followed by death in non-suid species. The risk to susceptible mammals was assumed to decrease when PRV was eliminated from U.S. commercial swine in 2004, though the virus remains endemic in feral swine. Infected feral swine pose a threat to the disease-free status of the commercial swine industry, and to other animals, including dogs, that come in direct or indirect contact with them. Since dogs are commonly used for hunting feral swine, they are at high risk of exposure. CASE PRESENTATION: The following report describes the progression of pseudorabies infection in dogs in two states after exposure to feral swine. The first case occurred in a dog in Alabama after participation in a competitive wild hog rodeo. The second case occurred in multiple dogs in Arkansas after hunting feral swine, and subsequent consumption of the offal. The antibody prevalence of feral swine in the two states where the dogs were exposed is also examined. CONCLUSIONS: Dogs that are used for hunting feral swine are at high risk of exposure to pseudorabies because the disease is considered endemic in feral swine in the U.S.

Raccoon (Procyon lotor) biomarker and rabies antibody response to varying oral rabies vaccine bait densities in northwestern Pennsylvania.

Distribution of oral rabies vaccine baits has been used as a strategy for managing rabies in the United States since the 1990s. Since that time, efforts have been made to improve baiting strategies with a focus on bait density to maximize both efficiency and cost effectiveness. An optimal rabies management strategy includes a vaccine bait preferred by the target species that is distributed at the minimal density needed to achieve population immunity to prevent rabies spread. The purpose of our pilot study was to examine the effect of 75, 150, and 300 baits/km2 vaccine bait densities on rabies virus neutralizing antibody (RVNA) seroprevalence in raccoons (Procyon lotor). Raboral V-RG® fishmeal polymer baits (Merial Inc. (now a part of Boehringer Ingelheim), Athens, Georgia) contain a tetracycline biomarker that was used to estimate bait consumption as another measure of intervention impact. Our results suggest that raccoon RVNA response increases as bait density increases, but the effect may not be sufficient to justify the cost except in the case of contingency actions or an epizootic. Non-target species, especially opossums (Didelphis virginianus) in certain areas, should be considered when determining an appropriate bait density to ensure sufficient baits are available for consumption by the target species.

Spillover of Swine Coronaviruses, United States.

Porcine epidemic diarrhea virus, a pathogen first detected in US domestic swine in 2013, has rapidly spilled over into feral swine populations. A better understanding of the factors associated with pathogen emergence is needed to better manage, and ultimately prevent, future spillover events from domestic to nondomestic animals.

LEPTOSPIRA ANTIBODIES DETECTED IN WILDLIFE IN THE USA AND THE US VIRGIN ISLANDS.

From 2011 to 2017, 4,534 serum samples from 13 wildlife species collected across the US and in one territory (US Virgin Islands) were tested for exposure to Leptospira serovars Bratislava, Canicola, Grippotyphosa, Hardjo, Icterohaemorrhagiae, and Pomona. Of 1,759 canids, 1,043 cervids, 23 small Indian mongooses ( Herpestes auropunctatus), 1,704 raccoons ( Procyon lotor), and five striped skunks ( Mephitis mephitis), 27.0, 44.4, 30.4, 40.8, and 60%, respectively, were antibody positive for any of the six serovars. The most commonly detected serovars across all species were Bratislava and Grippotyphosa. Our results indicate that Leptospira titers are very common in a wide variety of wildlife species. These species may act as important reservoirs in the epidemiological cycle of the pathogen. Additional studies to determine the relationship between serologic evidence and shedding of the pathogen by wildlife are necessary to better understand the risk.

Feral Swine in the United States Have Been Exposed to both Avian and Swine Influenza A Viruses.

Influenza A viruses (IAVs) in swine can cause sporadic infections and pandemic outbreaks among humans, but how avian IAV emerges in swine is still unclear. Unlike domestic swine, feral swine are free ranging and have many opportunities for IAV exposure through contacts with various habitats and animals, including migratory waterfowl, a natural reservoir for IAVs. During the period from 2010 to 2013, 8,239 serum samples were collected from feral swine across 35 U.S. states and tested against 45 contemporary antigenic variants of avian, swine, and human IAVs; of these, 406 (4.9%) samples were IAV antibody positive. Among 294 serum samples selected for antigenic characterization, 271 cross-reacted with ≥1 tested virus, whereas the other 23 did not cross-react with any tested virus. Of the 271 IAV-positive samples, 236 cross-reacted with swine IAVs, 1 with avian IAVs, and 16 with avian and swine IAVs, indicating that feral swine had been exposed to both swine and avian IAVs but predominantly to swine IAVs. Our findings suggest that feral swine could potentially be infected with both avian and swine IAVs, generating novel IAVs by hosting and reassorting IAVs from wild birds and domestic swine and facilitating adaptation of avian IAVs to other hosts, including humans, before their spillover. Continued surveillance to monitor the distribution and antigenic diversities of IAVs in feral swine is necessary to increase our understanding of the natural history of IAVs.IMPORTANCE There are more than 5 million feral swine distributed across at least 35 states in the United States. In contrast to domestic swine, feral swine are free ranging and have unique opportunities for contact with wildlife, livestock, and their habitats. Our serological results indicate that feral swine in the United States have been exposed to influenza A viruses (IAVs) consistent with those found in both domestic swine and wild birds, with the predominant infections consisting of swine-adapted IAVs. Our findings suggest that feral swine have been infected with IAVs at low levels and could serve as hosts for the generation of novel IAVs at the interface of feral swine, wild birds, domestic swine, and humans.

Antibodies to Various Zoonotic Pathogens Detected in Feral Swine (Sus scrofa) at Abattoirs in Texas, USA.

The zoonotic risk posed to employees by slaughtering feral swine (Sus scrofa) at two abattoirs in Texas was assessed by testing feral swine serum samples for exposure to influenza A virus, Leptospira, Trichinella spiralis, and Toxoplasma gondii. Blood was collected from a total of 376 feral swine between the two facilities during six separate collection periods in 2015. Antibodies to one or more serovars of Leptospira were identified in 48.9% of feral swine tested, with Bratislava and Pomona as the most commonly detected serovars, and antibodies to influenza A virus were detected in 14.1% of feral swine. Antibodies to T. gondii and T. spiralis were identified in 9.0 and 3.5%, respectively, of feral swine tested. Our results suggest that abattoir employees should be aware of the potential for exposure to various zoonotic pathogens when slaughtering feral swine, wear appropriate personal protective equipment, and participate in medical monitoring programs to ensure detection and prompt treatment. In addition, consumers of feral swine should cook the meat to the appropriate temperature and wash hands and kitchen surfaces thoroughly after preparing meat.

Serologic Evidence of Various Arboviruses Detected in White-Tailed Deer (Odocoileus virginianus) in the United States.

White-tailed deer (Odocoileus virginianus) are an abundant mammal with a wide geographic distribution in the United States, which make them good sentinels for monitoring arboviral activity across the country. Exposure to various arboviruses has been detected in white-tailed deer, typically in conjunction with another diagnostic finding. To better assess the exposure of white-tailed deer to seven arboviruses, we tested 1,508 sera collected from 2010 to 2016 for antibodies to eastern equine encephalitis (2.5%), Powassan (4.2%), St. Louis encephalitis, (3.7%), West Nile (6.0%), Maguari (19.4%), La Crosse (30.3%), and bluetongue (7.8%) viruses. At least one arbovirus was detected in 51.3%, and exposure to more than one arbovirus was identified in 17.6% of the white-tailed deer sampled.

LIMITED ANTIBODY EVIDENCE OF EXPOSURE TO MYCOBACTERIUM BOVIS IN FERAL SWINE (SUS SCROFA) IN THE USA.

Bovine tuberculosis is a chronic disease of cattle ( Bos taurus ) caused by the bacterium Mycobacterium bovis . Efforts have been made in the US to eradicate the disease in cattle, but spillover into wildlife and subsequent spillback have impeded progress in some states. In particular, infection in white-tailed deer ( Odocoileus virginianus ) has been followed by infection in cattle in some Midwestern states. Infection has also been documented in feral swine ( Sus scrofa ) on the Hawaiian island of Molokai and in various European countries, but no large-scale survey of antibody exposure to the bacteria has been conducted in feral swine in the US. We tested 488 sera from feral swine collected near previously documented outbreaks of bovine tuberculosis in cattle and captive cervids, in addition to 2,237 feral swine sera collected across the US from 1 October 2013 to 30 September 2014. While all but one of the samples were antibody negative, the results are important for establishing baseline negative data since feral swine are capable reservoirs and could be implicated in future outbreaks of the disease.

Seroprevalence of Neospora caninum in feral swine (Sus scrofa) in the United States.

The protozoon Neospora caninum is a major cause of abortion in cattle worldwide. Canids (Canis familiaris, Canis latrans, Canis lupus) are definitive hosts whereas many other animal species, including pigs, are intermediate hosts for the parasite. Between 2012 and 2014, serum samples from 1059 feral swine (Sus scrofa) from 29 states of the USA were tested for N. caninum antibodies, using the N. caninum agglutination test (NAT). Of these, 159 (15.0%) feral pigs from 21 states tested positive, with a range of titers of 1:25 (cut-off) (n=153), 1:200 (1), 1:400 (1), 1:800 (3) and 1:3200 (1). Results indicate widespread exposure of feral swine to N. caninum infection across the USA.

Feral swine virome is dominated by single-stranded DNA viruses and contains a novel Orthopneumovirus which circulates both in feral and domestic swine.

Feral swine are known reservoirs for various pathogens that can adversely affect domestic animals. To assess the viral ecology of feral swine in the USA, metagenomic sequencing was performed on 100 pooled nasal swabs. The virome was dominated by small, ssDNA viruses belonging to the families Circoviridae, Anelloviridae and Parvovirinae. Only four RNA viruses were identified: porcine kobuvirus, porcine sapelovirus, atypical porcine pestivirus and a novel Orthopneumovirus, provisionally named swine orthopneumovirus (SOV). SOV shared ~90 % nucleotide identity to murine pneumonia virus (MPV) and canine pneumovirus. A modified, commercially available ELISA for MPV found that approximately 30 % of both feral and domestic swine sera were positive for antibodies cross-reactive with MPV. Quantitative reverse transcription-PCR identified two (2 %) and four (5.0 %) positive nasal swab pools from feral and domestic swine, respectively, confirming that SOV circulates in both herds.

Identification of Avian Paramyxovirus Serotype-1 in Wild Birds in the USA.

In the US, sampling for avian paramyxovirus serotype-1 (APMV-1) is generally conducted when morbidity or mortality events occur involving certain families of wild birds known to be affected by the virus, such as cormorants (Family Phalacrocoracidae), pigeons, doves (Family Columbidae), or pelicans (Family Pelecanidae). To quantify the prevalence of APMV-1 in apparently healthy wild birds and to determine its geographic distribution, we collected swab and serum samples from >3,500 wild birds, representing eight orders from 1 January 2013 to 30 September 2013. Antibody prevalence was highest in wild birds of Order Suliformes (44.9%), followed by Pelecaniformes (24.4%), Anseriformes (22.7%), and Columbiformes (11.7%), with a relatively high occurrence of virulent viruses in Columbiformes (100% of virulent viruses isolated). As expected, viral shedding was comparatively much lower, and positives were only identified in Orders Accipitriformes (1.4%), Columbiformes (1.0%), Anseriformes (0.8%), and Charadriiformes (0.4%). We also demonstrate circulating virulent APMV-1 viruses of genotype VI in apparently healthy Rock Pigeons ( Columba livia ) from March through September in three states.

Widespread Detection of Antibodies to Eastern Equine Encephalitis, West Nile, St. Louis Encephalitis, and Turlock Viruses in Various Species of Wild Birds from Across the United States.

Wild birds serve as amplifying hosts for many arboviruses, and are thought to be responsible for introducing these viruses into new areas during migration as well as reintroducing them to places where winter temperatures disrupt mosquito-borne transmission. To learn more about four mosquito-borne arboviruses of concern to human or animal health, we tested sera from 997 wild birds of 54 species and 17 families across 44 states of the United States collected from January 1, 2013, through September 30, 2013. Samples were tested for antibody against eastern equine encephalitis, St. Louis encephalitis, West Nile, and Turlock viruses using plaque reduction neutralization tests with an endpoint of 80% or greater. Of the 333 (33.4%) birds that tested positive for antibody to at least one arbovirus, 29.7% were exposed to two or more arboviruses. Exposure to all four arboviruses was detected in Canada geese, double-crested cormorants, mallards, mute swans, laughing gulls, and American coots. Our results suggest that exposure to arboviruses is widespread in the United States across a diversity of wild bird species.

Dynamics of virus shedding and antibody responses in influenza A virus-infected feral swine.

Given their free-ranging habits, feral swine could serve as reservoirs or spatially dynamic 'mixing vessels' for influenza A virus (IAV). To better understand virus shedding patterns and antibody response dynamics in the context of IAV surveillance amongst feral swine, we used IAV of feral swine origin to perform infection experiments. The virus was highly infectious and transmissible in feral swine, and virus shedding patterns and antibody response dynamics were similar to those in domestic swine. In the virus-inoculated and sentinel groups, virus shedding lasted ≤ 6 and ≤ 9 days, respectively. Antibody titres in inoculated swine peaked at 1 : 840 on day 11 post-inoculation (p.i.), remained there until 21 days p.i. and dropped to < 1 : 220 at 42 days p.i. Genomic sequencing identified changes in wildtype (WT) viruses and isolates from sentinel swine, most notably an amino acid divergence in nucleoprotein position 473. Using data from cell culture as a benchmark, sensitivity and specificity of a matrix gene-based quantitative reverse transcription-PCR method using nasal swab samples for detection of IAV in feral swine were 78.9 and 78.1 %, respectively. Using data from haemagglutination inhibition assays as a benchmark, sensitivity and specificity of an ELISA for detection of IAV-specific antibody were 95.4 and 95.0 %, respectively. Serological surveillance from 2009 to 2014 showed that ∼7.58 % of feral swine in the USA were positive for IAV. Our findings confirm the susceptibility of IAV infection and the high transmission ability of IAV amongst feral swine, and also suggest the need for continued surveillance of IAVs in feral swine populations.