Several pathogens are known to affect the respiratory tract of pigs resulting in decreased health and welfare. Porcine parainfluenza virus 1 (PPIV1) and swine orthopneumovirus (SOV) have been identified as novel viruses in pigs. The pathogenicity of PPIV1 has been investigated experimentally by one research group, whereas SOV is yet to be studied. In this experimental trial, two groups of eight pigs were inoculated with a European isolate of PPIV1 or a pool of SOV RNA-positive clinical nasal swab material, and one group of four pigs with culture medium only (negative controls). Nasal swab samples were regularly collected to investigate viral RNA shedding, tissue samples for viral RNA and histopathological examinations, and blood samples to investigate seroconversion. All SOV inoculated pigs tested negative for SOV at 4 days post inoculation (DPI) and therefore, four of these pigs were transferred to the group with the PPIV1-infected pigs to assess direct-contact transmission. At DPI 4, two control and four pigs from each of the PPIV1 and SOV groups were euthanized and necropsied. The remaining pigs were euthanized at 14 DPI. No clinical signs, except for nasal discharge, were observed in any of the pigs. PPIV1 RNA shedding was observed from DPI 2-11 with peaks between DPI 4 and 7, and PPIV1 was transmitted horizontally to all direct-contact pigs. The highest viral RNA load was detected in the upper respiratory tract, i.e., nose, upper and lower trachea compared to the lower respiratory tract, i.e., bronchioles, and alveoli. Generally, a chronic tracheitis at 4 DPI, developing into chronic, erosive tracheitis at 14 DPI was observed in the PPIV1 groups and was supported by in situ detection of PPIV1 by RNAscope. Three pigs also developed mild, bronchointerstitial pneumonia at 14 DPI. All PPIV pigs euthanized at 14 DPI seroconverted. In conclusion, these results showed that PPIV1 is a primary porcine respiratory pathogen that causes breakage of the tracheal epithelial barrier and therefore can predispose to secondary infections. SOV's role as a porcine respiratory pathogen remains unknown, since no successful infection was established and it was not isolated in cells either.

Rotavirus A (RVA) causes viral gastroenteritis and is frequently detected in young piglets. These viruses are genotyped according to diversity within the outer capsid coding gene segments designated viral protein 4 (VP4) and 7 (VP7). The present study defines a comprehensive baseline for porcine RVA VP4 and VP7 genotypic diversity in Danish swine herds, important for future monitoring efforts. Disparities between amino acid residues in antigenic domains of the Danish RVA field viruses and the vaccine strain named 'Ohio State University (OSU) G5P[7]' were also investigated. RVA nucleic acids from positive faecal samples of 63/84 tested Danish swine herds were amplified using conventional reverse transcriptase polymerase chain reaction with primers specific for VP7 and VP4 genes and sequenced using Sanger or Illumina technologies. In total, 127 VP7 genes and 110 VP4 genes were sequenced and genotyped. Eight different VP7 genotypes (G2, G3, G4, G5, G9, G10, G11 and G26) and six different VP4 genotypes (P[6], P[7], P[13], P[23], P[26], and P[32]) together with two possibly new VP4 genotypes (P[X1] and P[X2]) were detected, and the most frequent genotype constellations were G9P[23], G9P[13], G5P[13], and G5P[23]. Nine rectal swabs from pigs of nine different herds revealed infections with multiple VP7 genotypes, and four swabs from pigs of four herds presented with various VP4 genotypes. Sampling of several pigs within the same herd revealed co-circulation of different genotypes, which emphasizes that several pigs should be sampled for representative RVA genotyping. Notable differences between the RVA field viruses and the vaccine strain were evident, as on average 11.7/29 and 25.8/37 amino acid residues in immunogenic domains differed in VP7 and VP4 genotypes, respectively. Considering the high RVA field strain diversity and their high divergence from the vaccine strains, future studies are needed to investigate the efficacy of available porcine RVA vaccines.

Several pathogens are known to affect the respiratory tract of pigs resulting in decreased health and welfare. Virological investigations and the use of metagenomic sequencing of samples allowed the identification of new viruses in pigs, such as porcine respirovirus type 1 (PRV1) and swine orthopneumovirus (SOV). The pathogenicity of PRV1 has been investigated experimentally by one research group, whereas SOV is yet to be studied. In this experimental trial, groups of weaners were inoculated with a European isolate of PRV1 ( n = 8), a pool of SOV RNA-positive clinical nasal swab material ( n = 8) or culture medium serving as controls ( n = 4). Four days post inoculation (DPI), two controls and four pigs from each of the PRV1 and SOV groups were euthanized and necropsied. All SOV inoculated pigs tested negative for SOV at DPI 4 and therefore four of these pigs were transferred to the stable with the PRV1- infected pigs to assess direct-contact transmission. Nasal swab samples were collected at regular intervals after challenge and blood samples were collected at DPI 0, 4, and 14. At 14 DPI, the remaining pigs ( n = 10) were euthanized and necropsied. Nasal swab samples and tissues from the respiratory tract were examined for PRV1 RNA by reverse transcriptase real- time PCR and blood samples were investigated for PRV1 antibodies by ELISA. Respiratory tissues were also evaluated macro- and microscopically and selected tissues were investigated for in situ detection of PRV1 mRNA by RNAscope. No clinical signs, except for nasal discharge, were observed in any of the pigs. PRV1-shedding was observed from DPI 2 to 11 with peaks between DPI 4 and 7, and PRV1 was transmitted horizontally to all direct-contact pigs. The highest viral load was detected in the upper respiratory tract, i.e. nose, upper and lower trachea compared to the lower respiratory tract, i.e., bronchioles, and alveoli. Generally, a chronic tracheitis at 4 DPI, developing into chronic, erosive tracheitis at 14 DPI was observed in the PRV1 groups and was supported by in situ detection of PRV1 by RNAscope. Three pigs also developed mild, bronchointerstitial pneumonia at 14 DPI. In conclusion, these results showed that PRV1 is a primary porcine respiratory pathogen. Author summary Respiratory diseases in pigs impair porcine health and welfare and are often caused by a complex interaction between pathogens. We investigated the pathogenesis of two recently discovered viruses: porcine respirovirus type 1 (PRV1) and swine orthopneumovirus (SOV). An experimental model in weaner pigs showed that PRV1 is capable of efficient replication, horizontal transmission and caused pathological manifestations mainly in the upper respiratory tract. The lesions consisted of chronic, erosive tracheitis in all PRV1 infected pigs, resulting in a breakage of the tracheal epithelial barrier, and a few pigs developed bronchointerstitial pneumonia. These findings confirm that PRV1 should be considered a primary porcine respiratory pathogen, but in contrast, SOV did not result in a successful infection, and the reasons why remain to be elucidated. ![Figure][1] Graphical abstract created with [Biorender.com][2] ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes [2]: https://Biorender.com

Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant porcine pathogen as it impairs reproduction and is a part of the porcine respiratory disease complex in pigs. PRRSV transmits through direct-contact but may also be transmitted over longer distances. Far-ultraviolet C (Far-UVC) radiation inactivates airborne microbes, including viruses, without causing harm to humans or animals. In this pilot study, several experiments were performed to establish an experimental model for airborne PRRSV-1 infection in pigs, and to assess the ability of Far-UVC radiation to reduce PRRSV-1 infections in pigs. In total, 48 pigs were exposed to varying doses of mesh-nebulized PRRSV-1 in different experimental setups. PRRSV-1 viremia was evaluated, and environmental contamination as well as air samples were assessed to investigate the presence of PRRSV-1 RNA. In the final setup of three replicate case-control trials, none of the case-pigs became infected with PRRSV-1, whereas two, one and zero of the controls were infected. These results indicate that Far-UVC exposure can reduce infection of airborne PRRSV-1 in an experimental inoculation model. The infection model does not consistently infect pigs - even with the highest dose of PRRSV-1, but mimics natural settings well, and therefore studies with similar setups are needed to confirm the ability of Far-UVC to reduce infection risk. This experimental setup, albeit it is not perfect, can also be used to investigate the potential effect on Far-UVC to prevent infection of other airborne viruses.

Surveillance of influenza A virus in swine populations is essential, from both a veterinary and public health perspective. Although some international organizations have published guidelines for swine influenza A virus (swIAV) surveillance, there is no standardized guidelines available and a clear overview of current existing surveillance activities is lacking at the European level. This study aimed to describe swIAV surveillance systems across Europe in 2022. An electronic survey was distributed to 41 member countries of the Cost Action “ESFLU”, resulting in 44 responses from 39 institutions representing 25 countries. The analysis identified 26 unique surveillance systems, operating at local, national, regional, and multi-national levels. The majority of the systems had the objective of surveilling emerging strains or monitoring for swine influenza viruses in herds. In 2022, approximately 3,500 farms were sampled, with piglets and weaners being the most sampled age groups. Most systems (n=23) used RT-PCR for detection and fourteen used sequencing for viral characterization/subtyping. The study also highlighted a strong reliance on passive surveillance. While data sharing with OFFLU and other public databases is advocated, nine systems consistently shared their data, while eleven others indicated that data sharing occurs conditionally, depending on specific circumstances. The study emphasized the need for harmonized guidelines for surveillance and the establishment of pipelines for the systematic collection and analysis of data in swIAV in pigs.

Major geographical transmission of porcine reproductive and respiratory syndrome virus (PRRSV) occurs via semen when a boar stud is infected. This happened in Denmark in 2019, providing an opportunity to compare previous experimental PRRSV boar studies with natural PRRSV-1 infection in boars. The aim of this study was to investigate the association between the presence of PRRSV RNA in serum, semen, testicles, and epididymis of boars naturally infected with PRRSV and to describe the histological lesions in the testes and epididymis combined with direct visualisation of PRRSV-infected cells by immunohistochemical staining (IHC). The exact timing of infection of each boar was not determined, but based on serology the boars were divided into two groups: acute and late infections. All boars included were sampled the same day. In this study, 35 boars and 10 healthy boars from another PRRSV-negative boar stud were included as histological controls. PRRSV RNA was found most often in serum (51%) and least frequently in semen (22%) and was more often detected in the reproductive tract in the acute phase of infection (p < 0.0001; RR: 2.58). Mononuclear cells and multinuclear giant cells were present in the adluminal compartment of the testis and epididymis in PRRSV-infected boars, but not in control boars (p < 0.05), which supports the hypothesis that macrophages are involved in the venereal spread of the virus.

Atypical porcine pestivirus (APPV) was first discovered in North America in 2015 and was later shown to be associated with congenital tremor (CT) in piglets. CT is an occasional challenge in some Danish sow herds. Therefore, we initiated an observational case control study to clarify a possible relationship between CT and APPV in Danish pig production. Blood samples were collected from piglets affected by CT (n = 55) in ten different sow herds and from healthy piglets in five sow herds without a history of CT piglets (n = 25), as well as one sow herd with a sporadic occurrence of CT (n = 5). APPV was detected by RT-qPCR in all samples from piglets affected by CT and in three out of five samples from piglets in the herd with a sporadic occurrence of CT. In the herds without a history of CT, only one out of 25 piglets were positive for APPV. In addition, farmers or veterinarians in CT-affected herds were asked about their experience of the issue. CT is most often seen in gilt litters, and a substantial increase in pre-weaning mortality is only observed in severe cases. According to our investigations, APPV is a common finding in piglets suffering from CT in Denmark.

In recent years, there has been a considerable increase in the use of Modified Live PRRSV Vaccines (MLV) for mass vaccination in Denmark. The potential risks and negative impact of this strategy have been sparsely studied. The aim of this study was to investigate the impact of quarterly sow mass vaccination in two Danish sow herds. The study was performed as an observational prospective cohort of 120 sows in each of two commercial breeding herds in a paired design. Blood samples were taken from sows and oral fluid samples from nursery pigs (four to ten weeks old) before and after vaccination. The presence of PRRSV-1 RNA was measured by real time quantitative reverse transcription-polymerase chain reaction (RT-qPCR), and the level of PRRSV-1 specific antibodies was measured by two different serological assays. PRRS virus was not detected in the sow herds two days before and two weeks after vaccination, but the vaccine strain virus was detected in the nursery pigs. The prevalence of sows without antibodies towards PRRSV-1 went from 6–15% before vaccination to 1–4% after vaccination depending on the serological assay used, despite the fact that they had previously been repeatedly vaccinated. Four sows tested negative for antibodies in both assays after vaccination.

Background: In July 2019, a PRRSV-negative boar station was infected with a new recombinant PRRSV‐1 virus strain, which subsequently spread to at least 36 herds that had received semen from the boar station. In the following months, all the infected herds reported reduced productivity. The aim of the present study was to evaluate the impact of the PRRS outbreak. Results: Production data were collected from 13 of the herds. The average levels of farrowings/week, liveborns/litter, stillborns/litter, pre-weaning mortality and weaned pigs/litter were compared for the five-month period after infection and the preceding seven months before infection with the new variant of PRRSV-1. Twelve herds experienced a decrease in farrowings/week (0.1-10.8 percent fewer farrowings/week), and all herds experienced fewer liveborns (0.8-4.8 fewer liveborns/litter) and more stillborns (0.6-2.6 more stillborns/litter). Pre-weaning mortality nearly doubled in half of the herds. Overall, the 13 herds were missing 2.4-6.5 pigs/litter at weaning during the five months after infection compared to the seven preceding months before infection. Conclusion: In this study, the impact of this new PRRSV-1 variant on productivity exceeded that typically seen in Danish herds infected with PRRSV-1.

Porcine reproductive and respiratory syndrome virus (PRRSV) is prevalent in Danish swine herds. In July 2019, PRRSV-1 was detected in a PRRSV-negative boar station and subsequently spread to more than 38 herds that had received semen from the boar station. Full genome sequencing revealed a sequence of 15.098 nucleotides. Phylogenetic analyses showed that the strain was a recombination between the Amervac strain (Unistrain PRRS vaccine; Hipra) and the 96V198 strain (Suvaxyn PRRS; Zoetis AH). The major parent was the 96V198 strain that spanned ORFs 1-2 and part of ORF 3 and the minor parent was the Amervac strain, which constituted the remaining part of the genome. The virus seems to be highly transmissible and has caused severe disease in infected herds despite a high level of genetic identity to the attenuated parent strains. The source of infection was presumable a neighbouring farm situated 5.8 km from the boar station.

Agreement between oral fluid and serum testing at herd and pen level was promising. The present results indicate that oral fluid testing for PRRSV at pen level has a high diagnostic specificity and a somewhat lower, but acceptable diagnostic sensitivity. These findings suggest that oral fluid testing using the real-time RT-PCR procedure established in this study is applicable for PRRS surveillance and diagnosis under Danish conditions.