Evaluation of internal farm biosecurity measures combined with sow vaccination to prevent influenza A virus infection in groups of due-to-wean pigs.

BACKGROUND: Influenza A virus (IAV) is an important respiratory pathogen of pigs that affects pig health, well-being and productivity, has zoonotic potential, and has significant economic impact for producers. The ultimate goal is to maintain herds free from IAV. Due to the probability of IAV introduction into the herds, it is also desirable for herds to have some immunity to the virus. In this study, we evaluated a protocol that combined sow vaccination with the implementation of internal biosecurity practices during the pre-weaning period with the goal to wean IAV negative pigs. Five IAV positive breeding herds were vaccinated twice, 3 weeks apart with a herd-specific autogenous vaccine. For the subsequent 8 weeks, a biosecurity protocol was maintained, consisting of no pig movements after 3 days of age, no use of nurse sows, workers changing disposable gloves between litters, workers not stepping into farrowing crates, and daily disinfection of tools and materials used to handle pigs. RESULTS: Following these interventions, four of the five treatment farms had significant reductions in IAV detection (p value < 0.05). Three of the farms tested negative at all sampling points post-intervention and one farm had a 21% reduction in IAV positivity. CONCLUSIONS: This study indicates that a protocol that combines sow vaccination and enhanced biosecurity practices may limit IAV transmission among piglets and enable the weaning of groups of pigs free from the virus.

Greater than 3-Log Reduction in Viable Coronavirus Aerosol Concentration in Ducted Ultraviolet-C (UV-C) Systems.

Control technologies to inactivate airborne viruses effectively are needed during the ongoing SARS-CoV-2 pandemic, and to guard against airborne transmitted diseases. We demonstrate that sealed UV-C flow reactors operating with fluences near 253 ± 1 nm of 13.9-49.6 mJ cm-2 efficiently inactivate coronaviruses in an aerosol. For measurements, porcine respiratory coronavirus (PRCV) was nebulized in a custom-built, 3.86 m wind tunnel housed in a biosafety level class II facility. The single pass log10 reduction of active coronavirus was in excess of 2.2 at a flow rate of 2439 L min-1 (13.9 mJ cm-2) and in excess of 3.7 (99.98% removal efficiency) at 684 L min-1 (49.6 mJ cm-2). Because virus titers resulting from sampling downstream of the UV-C reactor were below the limit of detection, the true log reduction is likely even higher than measured. Comparison of virus titration results to reverse transcriptase quantitative PCR and measurement of fluorescein concentrations (doped into the nebulized aerosol) reveals that the reduction in viable PRCV is primarily due to UV-C based inactivation, as opposed to physical collection of virus. The results confirm that UV-C flow reactors can efficiently inactivate coronaviruses through incorporation into HVAC ducts or recirculating air purifiers.

Wind tunnel-based testing of a photoelectrochemical oxidative filter-based air purification unit in coronavirus and influenza aerosol removal and inactivation.

Recirculating air purification technologies are employed as potential means of reducing exposure to aerosol particles and airborne viruses. Toward improved testing of recirculating air purification units, we developed and applied a medium-scale single-pass wind tunnel test to examine the size-dependent collection of particles and the collection and inactivation of viable bovine coronavirus (BCoV, a betacoronavirus), porcine respiratory coronavirus (PRCV, an alphacoronavirus), and influenza A virus (IAV), by a commercial air purification unit. The tested unit, the Molekule Air Mini, incorporates a MERV 16 filter as well as a photoelectrochemical oxidating layer. It was found to have a collection efficiency above 95.8% for all tested particle diameters and flow rates, with collection efficiencies above 99% for supermicrometer particles with the minimum collection efficiency for particles smaller than 100 nm. For all three tested viruses, the physical tracer-based log reduction was near 2.0 (99% removal). Conversely, the viable virus log reductions were found to be near 4.0 for IAV, 3.0 for BCoV, and 2.5 for PRCV, suggesting additional inactivation in a virus family- and genus-specific manner. In total, this work describes a suite of test methods which can be used to rigorously evaluate the efficacy of recirculating air purification technologies.

Transmission of influenza A virus and porcine reproductive and respiratory syndrome virus using a novel nurse sow model: a proof of concept.

The mechanisms of transmission of influenza A virus (IAV) and porcine reproductive and respiratory syndrome virus (PRRSV) in pigs during the pre-weaning period are not fully elucidated. Since viable IAV and PRRSV can be found on the udder skin of lactating sows and the use of nurse sows is a common management practice, we developed a novel nurse sow model to evaluate the transmission of IAV and PRRSV from lactating sows to their adopted piglets. In two studies, we infected pigs with either IAV or PRRSV who then contaminated the udder skin of lactating dams with their nasal and oral secretions while suckling. Once the skin was confirmed virus positive for IAV and PRRSV, the sows were moved to separate empty clean rooms to adopt IAV and PRRSV negative suckling piglets. After adoption, 1 out of eight (12.5%) piglets tested IAV positive 1-day post-adoption (dpa) and the entire litter (8 out of 8) became positive by 4 dpa. In the case of PRRSV, 3 out of 11 (27.3%) pigs tested rRT-PCR positive 2 dpa and there were 7 out of 11 (63.6%) pigs positive at the termination of the study at 7 dpa. This study documented the transmission of IAV and PRRSV between litters of piglets by nurse sows and highlights the importance of the nurse sow-piglet as a unit that contributes to the maintenance of endemic infections in breeding herds. The use of nurse sows in pig farms, though beneficial for minimizing pre-weaning mortality and maximizing farm productivity, is seemingly detrimental as this practice may facilitate the transmission of IAV and PRRSV to piglets prior to weaning.

Exploring heterologous prime-boost vaccination approaches to enhance influenza control in pigs.

Influenza A viruses evolve rapidly to escape host immunity. In swine, this viral evolution has resulted in the emergence of multiple H1 and H3 influenza A virus (IAV) lineages in the United States (US) pig populations. The heterologous prime-boost vaccination strategy is a promising way to deal with diverse IAV infection in multiple animal models. However, whether or not this vaccination strategy is applicable to US swine to impart immunity against infection from North American strains of IAV is still unknown. We performed a vaccination-challenge study to evaluate the protective efficacy of using multivalent inactivated vaccine and/or a live attenuated IAV vaccine (LAIV) in pigs following multiple prime-boost vaccination protocols against a simultaneous H1N1 and H3N2 IAV infection. Our data show that pigs in the heterologous prime-boost vaccination group had more favorable outcomes consistent with a better response against virus challenge than non-vaccinated pigs. Additionally, delivering a multivalent heterologous inactivated vaccine boost to pigs following a single LAIV administration was also beneficial. We concluded the heterologous prime boost vaccination strategy may potentiate responses to suboptimal immunogens and holds the potential applicability to control IAV in the North American swine industry. However, more studies are needed to validate the application of this vaccination approach under field conditions.

Human-Origin Influenza A(H3N2) Reassortant Viruses in Swine, Southeast Mexico.

The genetic diversity of influenza A viruses circulating in swine in Mexico complicates control efforts in animals and presents a threat to humans, as shown by influenza A(H1N1)pdm09 virus. To describe evolution of swine influenza A viruses in Mexico and evaluate strains for vaccine development, we sequenced the genomes of 59 viruses and performed antigenic cartography on strains from 5 regions. We found that genetic and antigenic diversity were particularly high in southeast Mexico because of repeated introductions of viruses from humans and swine in other regions in Mexico. We identified novel reassortant H3N2 viruses with genome segments derived from 2 different viruses that were independently introduced from humans into swine: pandemic H1N1 viruses and seasonal H3N2 viruses. The Mexico swine viruses are antigenically distinct from US swine lineages. Protection against these viruses is unlikely to be afforded by US virus vaccines and would require development of new vaccines specifically targeting these diverse strains.

Comparison of individual, group and environmental sampling strategies to conduct influenza surveillance in pigs.

BACKGROUND: Influenza A virus (IAV) is an important pathogen in pigs that affects productivity and has important public health implications because of its zoonotic nature. Surveillance is central to the control of influenza, however, detection of IAV infections can be challenging in endemically infected herds with low prevalence of infection. METHODS: In groups of suckling (18-21 days of age) and growing (35-45 days of age) pigs, we compared various sampling approaches to detect, isolate and sequence IAV using individual (nasal swabs, nasal wipes and oropharyngeal swabs), group (oral fluids, surface wipes and sow udder skin wipes) and environmental (airborne particles deposited on surfaces and air samples) sampling approaches. All samples were tested by IAV rRT-PCR and a subset was used for virus isolation and direct sequencing. RESULTS: In general, environmental and group samples resulted in higher odd ratios (range = 3.87-16.5, p-value < 0.05) of detecting a positive sample by rRT-PCR compared to individual pooled samples, except for oropharyngeal swabs (OR = 8.07, p-value < 0.05). In contrast, individual samples were most likely to yield a viral isolate by cell culture. Oropharyngeal swabs in suckling pigs (78.4%), and nasal swabs (47.6%) or nasal wipes (45%) in growing pigs, and udder wipes in lactating sows (75%) were the preferred samples to obtain an isolate. CONCLUSIONS: Our findings indicate that group and environmental sampling strategies should be considered in influenza surveillance programs in particular if the goal is just to detect infection. This study provides new information on sampling approaches to conduct effective influenza surveillance in pigs and identifies udder wipes from lactating sows as a novel sample type that offers a convenient, cheap and sensitive manner to monitor IAV in litters prior to weaning.

Complete Genome Sequencing of Influenza A Viruses within Swine Farrow-to-Wean Farms Reveals the Emergence, Persistence, and Subsidence of Diverse Viral Genotypes.

Influenza A viruses (IAVs) are endemic in swine and represent a public health risk. However, there is limited information on the genetic diversity of swine IAVs within farrow-to-wean farms, which is where most pigs are born. In this longitudinal study, we sampled 5 farrow-to-wean farms for a year and collected 4,190 individual nasal swabs from three distinct pig subpopulations. Of these, 207 (4.9%) samples tested PCR positive for IAV, and 124 IAVs were isolated. We sequenced the complete genomes of 123 IAV isolates and found 31 H1N1, 26 H1N2, 63 H3N2, and 3 mixed IAVs. Based on the IAV hemagglutinin, seven different influenza A viral groups (VGs) were identified. Most of the remaining IAV gene segments allowed us to differentiate the same VGs, although an additional viral group was identified for gene segment 3 (PA). Moreover, the codetection of more than one IAV VG was documented at different levels (farm, subpopulation, and individual pigs), highlighting the environment for potential IAV reassortment. Additionally, 3 out of 5 farms contained IAV isolates (n = 5) with gene segments from more than one VG, and 79% of all the IAVs sequenced contained a signature mutation (S31N) in the matrix gene that has been associated with resistance to the antiviral amantadine. Within farms, some IAVs were detected only once, while others were detected for 283 days. Our results illustrate the maintenance and subsidence of different IAVs within swine farrow-to-wean farms over time, demonstrating that pig subpopulation dynamics are important to better understand the diversity and epidemiology of swine IAVs.IMPORTANCE On a global scale, swine are one of the main reservoir species for influenza A viruses (IAVs) and play a key role in the transmission of IAVs between species. Additionally, the 2009 IAV pandemics highlighted the role of pigs in the emergence of IAVs with pandemic potential. However, limited information is available regarding the diversity and distribution of swine IAVs on farrow-to-wean farms, where novel IAVs can emerge. In this study, we studied 5 swine farrow-to-wean farms for a year and characterized the genetic diversity of IAVs among three different pig subpopulations commonly housed on this type of farm. Using next-generation-sequencing technologies, we demonstrated the complex distribution and diversity of IAVs among the pig subpopulations studied. Our results demonstrated the dynamic evolution of IAVs within farrow-to-wean farms, which is crucial to improve health interventions to reduce the risk of transmission between pigs and from pigs to people.

Evaluation of biosecurity measures to prevent indirect transmission of porcine epidemic diarrhea virus.

BACKGROUND: The effectiveness of biosecurity methods to mitigate the transmission of porcine epidemic diarrhea virus (PEDV) via farm personnel or contaminated fomites is poorly understood. This study was undertaken to evaluate the effectiveness of biosecurity procedures directed at minimizing transmission via personnel following different biosecurity protocols using a controlled experimental setting. RESULTS: PEDV RNA was detected from rectal swabs of experimentally infected (INF) and sentinel pigs by real-time reverse transcription polymerase chain reaction (rRT-PCR). Virus shedding in INF pigs peaked at 1 day post infection (dpi) and viral RNA levels remained elevated through 19 dpi. Sentinel pigs in the low biosecurity group (LB) became PEDV positive after the first movement of study personnel from the INF group. However, rectal swabs from pigs in the medium biosecurity (MB) and high biosecurity (HB) groups were negative during the 10 consecutive days of movements and remained negative through 24 days post movement (dpm) when the first trial was terminated. Viral RNA was detected at 1 dpm through 3 dpm from the personal protective equipment (PPE) of LB personnel. In addition, at 1 dpm, 2 hair/face swabs from MB personnel were positive; however, transmission of virus was not detected. All swabs of fomite from the HB study personnel were negative. CONCLUSIONS: These results indicate that indirect PEDV transmission through contaminated PPE occurs rapidly (within 24 h) under modeled conditions. Biosecurity procedures such as changing PPE, washing exposed skin areas, or taking a shower are recommended for pig production systems and appear to be an effective option for lowering the risk of PEDV transmission between groups of pigs.

Evaluation of an electrostatic particle ionization technology for decreasing airborne pathogens in pigs.

Influenza A virus (IAV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV) and Staphylococcus aureus are important swine pathogens capable of being transmitted via aerosols. The electrostatic particle ionization system (EPI) consists of a conductive line that emits negative ions that charge particles electrically resulting in the settling of airborne particles onto surfaces and potentially decreasing the risk of pathogen dissemination. The objectives of this study were to determine the effect of the EPI system on the quantity and viability of IAV, PRRSV, PEDV and S. aureus in experimentally generated aerosols and in aerosols generated by infected animals. Efficiency at removing airborne particles was evaluated as a function of particle size (ranging from 0.4 to 10 µm), distance from the source of ions (1, 2 and 3 m) and relative air humidity (RH 30 vs. 70 %). Aerosols were sampled with the EPI system "off" and "on." Removal efficiency was significantly greater for all pathogens when the EPI line was the closest to the source of aerosols. There was a greater reduction for larger particles ranging between 3.3 and 9 µm, which varied by pathogen. Overall airborne pathogen reduction ranged between 0.5 and 1.9 logs. Viable pathogens were detected with the EPI system "on," but there was a trend to reducing the quantity of viable PRRSV and IAV. There was not a significant effect on the pathogens removal efficiency based on the RH conditions tested. In summary, distance to the source of ions, type of pathogen and particle size influenced the removal efficiency of the EPI system. The reduction in infectious agents in the air by the EPI technology could potentially decrease the microbial exposure for pigs and people in confinement livestock facilities.

Modeling risk of occupational zoonotic influenza infection in swine workers.

Zoonotic transmission of influenza A virus (IAV) between swine and workers in swine production facilities may play a role in the emergence of novel influenza strains with pandemic potential. Guidelines to prevent transmission of influenza to swine workers have been developed but there is a need for evidence-based decision-making about protective measures such as respiratory protection. A mathematical model was applied to estimate the risk of occupational IAV exposure to swine workers by contact and airborne transmission, and to evaluate the use of respirators to reduce transmission. The Markov model was used to simulate the transport and exposure of workers to IAV in a swine facility. A dose-response function was used to estimate the risk of infection. This approach is similar to methods previously used to estimate the risk of infection in human health care settings. This study uses concentration of virus in air from field measurements collected during outbreaks of influenza in commercial swine facilities, and analyzed by polymerase chain reaction. It was found that spending 25 min working in a barn during an influenza outbreak in a swine herd could be sufficient to cause zoonotic infection in a worker. However, this risk estimate was sensitive to estimates of viral infectivity to humans. Wearing an excellent fitting N95 respirator reduced this risk, but with high aerosol levels the predicted risk of infection remained high under certain assumptions. The results of this analysis indicate that under the conditions studied, swine workers are at risk of zoonotic influenza infection. The use of an N95 respirator could reduce such risk. These findings have implications for risk assessment and preventive programs targeting swine workers. The exact level of risk remains uncertain, since our model may have overestimated the viability or infectivity of IAV. Additionally, the potential for partial immunity in swine workers associated with repeated low-dose exposures or from previous infection with other influenza strains was not considered. Further studies should explore these uncertainties.

Swine Worker Precautions During Suspected Outbreaks of Influenza in Swine.

To assess the behavior and precautions that swine workers take during suspected influenza outbreaks in swine, six commercial swine farms in the Midwest U.S. region were visited when influenza outbreaks were suspected in herds during the fall/winter of 2012-2013. Use of personal protective equipment (PPE) and type of task performed by swine workers were recorded based on farm representative reports. Between one to two workers were working on the day of each visit and spent approximately 25 minutes performing work-related tasks that placed them in close contact with the swine. The most common tasks reported were walking the aisles (27%), handling pigs (21%), and handling equipment (21%). The most common PPE were boots (100%), heavy rubber gloves (75%), and dedicated nondisposable clothing (74%). Use of N95 respirators was reported at three farms. Hand hygiene practices were common in most of the farms, but reportedly performed for only 20% to 25% of tasks.

Live Animal Markets in Minnesota: A Potential Source for Emergence of Novel Influenza A Viruses and Interspecies Transmission.

BACKGROUND: Live animal markets have been implicated in transmission of influenza A viruses (IAVs) from animals to people. We sought to characterize IAVs at 2 live animal markets in Minnesota to assess potential routes of occupational exposure and risk for interspecies transmission. METHODS: We implemented surveillance for IAVs among employees, swine, and environment (air and surfaces) during a 12-week period (October 2012-January 2013) at 2 markets epidemiologically associated with persons with swine-origin IAV (variant) infections. Real-time reverse transcription polymerase chain reaction (rRT-PCR), viral culture, and whole-genome sequencing were performed on respiratory and environmental specimens, and serology on sera from employees at beginning and end of surveillance. RESULTS: Nasal swabs from 11 of 17 (65%) employees tested positive for IAVs by rRT-PCR; 7 employees tested positive on multiple occasions and 1 employee reported influenza-like illness. Eleven of 15 (73%) employees had baseline hemagglutination inhibition antibody titers ≥40 to swine-origin IAVs, but only 1 demonstrated a 4-fold titer increase to both swine-origin and pandemic A/Mexico/4108/2009 IAVs. IAVs were isolated from swine (72/84), air (30/45), and pen railings (5/21). Whole-genome sequencing of 122 IAVs isolated from swine and environmental specimens revealed multiple strains and subtype codetections. Multiple gene segment exchanges among and within subtypes were observed, resulting in new genetic constellations and reassortant viruses. Genetic sequence similarities of 99%-100% among IAVs of 1 market customer and swine indicated interspecies transmission. CONCLUSIONS: At markets where swine and persons are in close contact, swine-origin IAVs are prevalent and potentially provide conditions for novel IAV emergence.

Genome plasticity of triple-reassortant H1N1 influenza A virus during infection of vaccinated pigs.

To gain insight into the evolution of influenza A viruses (IAVs) during infection of vaccinated pigs, we experimentally infected a 3-week-old naive pig with a triple-reassortant H1N1 IAV and placed the seeder pig in direct contact with a group of age-matched vaccinated pigs (n = 10). We indexed the genetic diversity and evolution of the virus at an intra-host level by deep sequencing the entire genome directly from nasal swabs collected at two separate samplings during infection. We obtained 13 IAV metagenomes from 13 samples, which included the virus inoculum and two samples from each of the six pigs that tested positive for IAV during the study. The infection produced a population of heterogeneous alleles (sequence variants) that was dynamic over time. Overall, 794 polymorphisms were identified amongst all samples, which yielded 327 alleles, 214 of which were unique sequences. A total of 43 distinct haemagglutinin proteins were translated, two of which were observed in multiple pigs, whereas the neuraminidase (NA) was conserved and only one dominant NA was found throughout the study. The genetic diversity of IAVs changed dynamically within and between pigs. However, most of the substitutions observed in the internal gene segments were synonymous. Our results demonstrated remarkable IAV diversity, and the complex, rapid and dynamic evolution of IAV during infection of vaccinated pigs that can only be appreciated with repeated sampling of individual animals and deep sequence analysis.

Haemophilus parasuis: infection, immunity and enrofloxacin.

Haemophilus parasuis is an early colonizer of the porcine upper respiratory tract and is the etiological agent of Glasser's disease. The factors responsible for H. parasuis colonization and systemic infection are not yet well understood, while prevention and control of Glasser's disease continues to be challenging. Recent studies on innate immunity to H. parasuis have demonstrated that porcine alveolar macrophages (PAMs) are able to differentially up-regulate several genes related to inflammation and phagocytosis, and several pro-inflammatory cytokines are produced by porcine cells upon exposure to H. parasuis. The susceptibility of H. parasuis strains to phagocytosis by PAMs and the bactericidal effect of complement are influenced by the virulent phenotype of the strains. While non-virulent strains are susceptible to phagocytosis and complement, virulent strains are resistant to both. However, in the presence of specific antibodies against H. parasuis, virulent strains become susceptible to phagocytosis. More information is still needed, though, in order to better understand the host immune responses to H. parasuis. Antimicrobials are commonly used in the swine industry to help treat and control Glasser's disease. Some of the common antimicrobials have been shown to reduce colonization by H. parasuis, which may have implications for disease dynamics, development of effective immune responses and immunomodulation. Here, we provide the current state of research on innate and adaptive immune responses to H. parasuis and discuss the potential effect of enrofloxacin on the development of a protective immune response against H. parasuis infection.

Diagnostics and surveillance for Swine influenza.

Collective knowledge regarding the occurrence of influenza among swine is incomplete due to inconsistent surveillance of swine populations. In this chapter, we review what surveillance activities exist and some of the practical challenges encountered. Furthermore, to support robust surveillance activities, accurate laboratory assays are needed for the detection of the virus and viral nucleic acids within clinical samples, or for antiviral antibodies in serum samples. The most common influenza diagnostic assays used for swine are explained and their use as surveillance tools evaluated.

Evidence of infectivity of airborne porcine epidemic diarrhea virus and detection of airborne viral RNA at long distances from infected herds.

Porcine epidemic diarrhea virus (PEDV) spread rapidly after being diagnosed in the USA in April 2013. In this study we assessed whether PEDV could become airborne and if so, whether the virus was infectious. Air samples were collected both from a room containing experimentally infected pigs and at various distances from the outside of swine farms experiencing acute PEDV outbreaks. Results indicated presence of infectious PEDV in the air from experimentally infected pigs and genetic material of PEDV was detected up to 10 miles downwind from naturally infected farms. Airborne transmission should be considered as a potential route for PEDV dissemination.

Biosecurity Insights from the United States Swine Health Improvement Plan: Analyzing Data to Enhance Industry Practices.

Biosecurity practices aim to reduce the frequency of disease outbreaks in a farm, region, or country and play a pivotal role in fortifying the country's pork industry against emerging threats, particularly foreign animal diseases (FADs). This article addresses the current biosecurity landscape of the US swine industry by summarizing the biosecurity practices reported by the producers through the United States Swine Health Improvement Plan (US SHIP) enrollment surveys, and it provides a general assessment of practices implemented. US SHIP is a voluntary, collaborative effort between industry, state, and federal entities regarding health certification programs for the swine industry. With 12,195 sites surveyed across 31 states, the study provides a comprehensive snapshot of current biosecurity practices. Key findings include variability by site types that have completed Secure Pork Supply plans, variability in outdoor access and presence of perimeter fencing, and diverse farm entry protocols for visitors. The data also reflect the industry's response to the threat of FADs, exemplified by the implementation of the US SHIP in 2020. As the US SHIP program advances, these insights will guide industry stakeholders in refining biosecurity practices, fostering endemic re-emerging and FAD preparedness, and ensuring the sustainability of the swine industry in the face of evolving challenges.

Novel influenza A viruses in pigs with zoonotic potential, Chile.

Novel H1N2 and H3N2 swine influenza A viruses (IAVs) have recently been identified in Chile. The objective of this study was to evaluate their zoonotic potential. We perform phylogenetic analyses to determine the genetic origin and evolution of these viruses, and a serological analysis to determine the level of cross-protective antibodies in the human population. Eight genotypes were identified, all with pandemic H1N1 2009-like internal genes. H1N1 and H1N2 were the subtypes more commonly detected. Swine H1N2 and H3N2 IAVs had hemagglutinin and neuraminidase lineages genetically divergent from IAVs reported worldwide, including human vaccine strains. These genes originated from human seasonal viruses were introduced into the swine population since the mid-1980s. Serological data indicate that the general population is susceptible to the H3N2 virus and that elderly and young children also lack protective antibodies against the H1N2 strains, suggesting that these viruses could be potential zoonotic threats. Continuous IAV surveillance and monitoring of the swine and human populations is strongly recommended.IMPORTANCEIn the global context, where swine serve as crucial intermediate hosts for influenza A viruses (IAVs), this study addresses the pressing concern of the zoonotic potential of novel reassortant strains. Conducted on a large scale in Chile, it presents a comprehensive account of swine influenza A virus diversity, covering 93.8% of the country's industrialized swine farms. The findings reveal eight distinct swine IAV genotypes, all carrying a complete internal gene cassette of pandemic H1N1 2009 origin, emphasizing potential increased replication and transmission fitness. Genetic divergence of H1N2 and H3N2 IAVs from globally reported strains raises alarms, with evidence suggesting introductions from human seasonal viruses since the mid-1980s. A detailed serological analysis underscores the zoonotic threat, indicating susceptibility in the general population to swine H3N2 and a lack of protective antibodies in vulnerable demographics. These data highlight the importance of continuous surveillance, providing crucial insights for global health organizations.

Infection dynamics and incidence of wild-type porcine reproductive and respiratory syndrome virus in growing pig herds in the U.S. Midwest.

Porcine reproductive and respiratory syndrome virus (PRRSV) infections greatly impact the health and productivity of growing pigs. The introduction and persistence of wild-type PRRSV (WT-PRRSV) strains in growing pig populations is poorly understood. In an observational prospective cohort study, we monitored and surveyed 63 wean-to-finish (WTF) herds across 10 companies located in medium to high pig dense areas in the U.S. Midwest. All herds received weaned pigs from PRRSV-negative or positive-stable breeding herds. Herds were monitored monthly using oral fluids collected following a fixed spatial sampling regime and samples were tested by PRRSV ELISA, RT-PCR and ORF5 sequencing. In most (90%) of the herds, pigs were vaccinated with PRRSV modified-live vaccines either at processing, weaning or shortly after weaning. Wild type PRRSV (WT-PRRSV) infections were defined by the criterion of having more than 2% nucleotide differences in the ORF-5 region compared with reference vaccine strain sequences. Wild type PRRSV was detected in 42% of the herds with infections being more prevalent in the mid to late growing period, with a mean of 20 weeks post placement. Nineteen distinct WT-PRRSV were identified in seven out of 10 production companies with an average of 3 distinct WT-PRRSV strains per company. Vaccinated WTF herds with and without WT-PRRSV detection were compared to each other showing different PCR and ELISA infection patterns. Close-out mortality in vaccinated herds with WT-PRRSV was numerically higher (6.5%) than mortality in those sites where WT-PRRSV was not detected (5.0%) (p = 0.07). Mortality was also higher (10.5%) when WT-PRRSV was detected earlier at eight weeks post-placement compared to late finishing at 20 and 25 weeks post-placement, 2.9% and 4.5% respectively (p = 0.017). Overall, this study sheds light on WT-PRRSV infection dynamics in vaccinated populations of growing pigs, reinforces the importance of biosecurity practices in this phase of production and calls for better understanding of risk factors associated with PRRSV introductions in growing pig sites.