Summary Influenza A virus infections cause respiratory disease in pigs and are a risk to public health. The pig plays an important role in influenza ecology because of its ability to support replication of influenza viruses from avian, swine and human species. Influenza A virus is widespread in pigs worldwide, and influenza A virus interspecies transmission has been documented in many events. Influenza A virus is mostly transmitted through direct pig‐to‐pig contact and aerosols although other indirect routes of transmission may also exist. Several factors contribute to differences in the transmission dynamics within populations including among others vaccination, pig flow, animal movement and animal introduction which highlights the complexity of influenza A transmission in pigs. In addition, pigs can serve as a reservoir of influenza A viruses for other pigs and other species and understanding mechanisms of transmission within pigs and from pigs to other species and vice versa is crucial. In this paper, we review the current understanding of influenza virus transmission in pigs. We highlight the ubiquity of influenza A virus in the pig population and the widespread distribution of pandemic H1N1 virus worldwide while emphasizing an understanding of the routes of transmission and factors that contribute to virus spread and dissemination within and between pig populations. In addition, we describe transmission events between pigs and other species including people. Understanding transmission is crucial for designing effective control strategies and for making well‐informed recommendations for surveillance.

Porcine deltacoronavirus (PDCoV) was identified in multiple states across the United States (US) in 2014. In this study, we investigate the presence of PDCoV in diagnostic samples, which were further categorized by case identification (ID), and the association between occurrence, age, specimen and location between March and September 2014. Approximately, 7% of the case IDs submitted from the US were positive for PDCoV. Specimens were categorized into eight groups, and the univariate analysis indicated that oral fluids had 1.89 times higher odds of detecting PDCoV compared to feces. While the 43-56 day age group had the highest percentage of PDCoV positives (8.4%), the univariate analysis indicated no significant differences between age groups. However, multivariable analysis for age adjusted by specimen indicated the >147 day age group had 59% lower odds than suckling pigs of being positive for PDCoV. The percentage of PDCoV in diagnostic samples decreased to <1% in September 2014. In addition, 19 complete PDCoV genomes were sequenced, and Bayesian analysis was conducted to estimate the emergence of the US clade. The evolutionary rate of the PDCoV genome is estimated to be 3.8×10(-4) substitutions/site/year (2.3×10(-4)-5.4×10(-4), 95% HPD). Our results indicate that oral fluids continue to be a valuable specimen to monitor swineherd health, and PDCoV has been circulating in the US prior to 2014.

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.

Influenza A viruses (IAVs) are distributed worldwide in birds, pigs and humans, and cause important endemic disease affecting hosts in all countries. Although pigs play a key role in the ecology of IAVs, the epidemiology of IAVs within swine herds is poorly understood. In this longitudinal study we describe the prevalence of IAVs infection in three subpopulations of pigs in 5 breeding herds in the Midwestern USA. Each herd was sampled monthly for a year and, at each visit, 30 individual nasal swabs were collected from the three subpopulations, namely, a) replacement females, resident on-farm for less than 4 weeks (new gilts), b) replacement females, resident on-farm for more than 4 weeks (gilts), and c) neonatal pigs less than 21 days of age (piglets). Real time reverse transcriptase polymerase chain reaction (RRT-PCR) was used to detect IAVs, and the association between IAVs infection and pig subpopulation was measured using a mixed logistic regression model. Nasal swabs (n = 4,190) were collected from 141 groups of pigs. At least, one IAV-positive nasal swab was found in 19.9% (n = 28) of the sampled groups, and 7.7% (n = 324) of all nasal swabs tested positive. After adjusting by annual quarter and sampling event, the odds of testing IAV positive were 7.9 (95% CI 1.4, 43.9) and 4.4 (95% CI 1.1, 17.1) times higher in groups of new gilts and piglets compared to groups of gilts, respectively. Results indicate that new gilts and piglets had higher odds of testing IAV positive than gilts in swine breeding herds and that season influences IAV infection in pigs. Based on these findings, we recommend that IAV control strategies be aimed at preventing infection before gilts are introduced into the farm, and in pigs prior to weaning.

Avian influenza or bird flu is a highly contagious acute viral disease that can occur in epidemics and cross-border forms in poultry and wild birds. The characteristics of avian influenza viruses (AIVs) allow the emergence of new viral variants, some with zoonotic and pandemic potential. AIVs have been identified in Latin America; however, there is a lack of understanding of these viruses at the regional level. We performed a systematic literature review on serological or molecular evidence of AIVs circulation in Latin America. Methods were designed based on the PRISMA and STROME guidelines. Only peer-reviewed studies published between 2000 to 2015 and data was analysed based on country, viral subtype, avian species, and phylogenetic origins. From 271 studies initially found only twenty-six met our inclusion criteria. Evidence of AIVs infection was found in most Latin American countries, with Mexico as the country with the largest number of conducted studies and reported cases during the period analysed, followed by Chile and Argentina. Most of the AIVs were early reported through surveillance systems and at least 14 different subtypes of influenza viruses were reported in birds, and the presence of both low (92.9%) and high (7.1%) pathogenic AIVs was shown in Latin America. Of the reported AIVs in Latin America, 43.7% belong to migratory birds, 28.1% to local wild birds, and 28.1% to poultry. The migratory bird population mainly comprises families belonging to the orders Anseriformes and Charadriformes. We highlight the importance of epidemiological surveillance systems and the possible role of different migratory birds in the transmission of AIVs within the Americas. Our findings demonstrate the limited information on AIVs in Latin America and highlight the need of more studies on AIVs at the regional level, particularly those focused on identifying the endemic subtypes in regional wild birds.