The role of gilts in transmission dynamics of swine influenza virus and impacts of vaccination strategies and quarantine management

Dynamic of swine influenza virus infection in weaned piglets in five enzootically infected herds in Germany, a cohort study

BACKGROUND

Within the last decades industrial swine herds in Europe grown significantly, creating an optimized reservoir for swine influenza A viruses (swIAV) to become enzootic, particularly in piglet producing herds among newborn, partly immunologically naïve piglets. To date, the only specific control measure to protect piglets from swIAV is the vaccination of sows, which provides passive immunity through maternally derived antibodies in colostrum of vaccinated sows. Interruption of infection chains through management practices have had limited success. This study focused on weaned piglets in five enzootically swIAV infected swine herds in North-West and North-East Germany and aimed to better understand swIAV infection patterns to improve piglet protection and reduce zoonotic risks. Participating farms fulfilled the following inclusion criteria: sow herd with ≥ 400 sows (actual size 600-1850 sows), piglets not vaccinated against influenza A virus and a history of recurrent respiratory problems associated with continuing influenza A virus infection. Influenza vaccination was performed in all sow herds, except for one, which discontinued vaccination during the study.

RESULTS

First swIAV detections in weaned piglets occurred at 4 weeks of age in the nursery and continued to be detected in piglets up to 10 weeks of age showing enzootic swIAV infections in all herds over the entire nursery period. This included simultaneous circulation of two subtypes in a herd and co-infection with two subtypes in individual animals. Evidence for prolonged (at least 13 days) shedding was obtained in one piglet based on two consecutive swIAV positive samplings. Possible re-infection was suspected in twelve piglets based on three samplings, the second of which was swIAV negative in contrast to the first and third sampling which were swIAV positive. However, swIAV was not detected in nasal swabs from either suckling piglets or sows in the first week after farrowing.

CONCLUSIONS

Predominantly, weaned piglets were infected. There was no evidence of transmission from sow to piglet based on swIAV negative nasal swabs from sows and suckling piglets. Prolonged virus shedding by individual piglets as well as the co-circulation of different swIAV subtypes in a group or even individuals emphasize the potential of swIAV to increase genetic (and potentially phenotypic) variation and the need to continue close monitoring. Understanding the dynamics of swIAV infections in enzootically infected herds has the overall goal of improving protection to reduce economic losses due to swIAV-related disease and consequently to advance animal health and well-being.

Sequence-Based Antigenic Analyses of H1 Swine Influenza A Viruses from Colombia (2008-2021) Reveals Temporal and Geographical Antigenic Variations

Swine influenza is a respiratory disease that affects the pork industry and is a public health threat. It is caused by type A influenza virus (FLUAV), which continuously undergoes genetic and antigenic variations. A large amount of information regarding FLUAV in pigs is available worldwide, but it is limited in Latin America. The HA sequences of H1 subtype FLUAV-positive samples obtained from pigs in Colombia between 2008-2021 were analyzed using sequence-based antigenic cartography and N-Glycosylation analyses. Of the 12 predicted global antigenic groups, Colombia contained five: four corresponding to pandemic strains and one to the classical swine H1N1 clade. Circulation of these clusters was observed in some regions during specific years. Ca2 was the immunodominant epitope among Colombian viruses. The counts of N-Glycosylation motifs were associated with the antigenic cluster ranging from three to five. The results show for the first time the existence of antigenic diversity of FLUAV in Colombia and highlight the impact of spatial and temporal factors on this diversity. This study provides information about FLUAV variability in pigs under natural conditions in the absence of vaccination and emphasizes the need for surveillance of its phylogenetic and antigenic characteristics.

Porcine respiratory disease complex: Dynamics of polymicrobial infections and management strategies after the introduction of the African swine fever

A few decades ago, porcine respiratory disease complex (PRDC) exerted a major economic impact on the global swine industry, particularly due to the adoption of intensive farming by the latter during the 1980's. Since then, the emerging of porcine reproductive and respiratory syndrome virus (PRRSV) and of porcine circovirus type 2 (PCV2) as major immunosuppressive viruses led to an interaction with other endemic pathogens (e.g., Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Streptococcus suis, etc.) in swine farms, thereby exacerbating the endemic clinical diseases. We herein, review and discuss various dynamic polymicrobial infections among selected swine pathogens. Traditional biosecurity management strategies through multisite production, parity segregation, batch production, the adoption of all-in all-out production systems, specific vaccination and medication protocols for the prevention and control (or even eradication) of swine diseases are also recommended. After the introduction of the African swine fever (ASF), particularly in Asian countries, new normal management strategies minimizing pig contact by employing automatic feeding systems, artificial intelligence, and robotic farming and reducing the numbers of vaccines are suggested. Re-emergence of existing swine pathogens such as PRRSV or PCV2, or elimination of some pathogens may occur after the ASF-induced depopulation. ASF-associated repopulating strategies are, therefore, essential for the establishment of food security. The "repopulate swine farm" policy and the strict biosecurity management (without the use of ASF vaccines) are, herein, discussed for the sustainable management of small-to-medium pig farms, as these happen to be the most potential sources of an ASF re-occurrence. Finally, the ASF disruption has caused the swine industry to rapidly transform itself. Artificial intelligence and smart farming have gained tremendous attention as promising tools capable of resolving challenges in intensive swine farming and enhancing the farms' productivity and efficiency without compromising the strict biosecurity required during the ongoing ASF era.

A New Sampling Approach for the Detection of Swine Influenza a Virus on European Sow Farms

Simple Summary

Due to concerns in public health and its negative impact on the pig industry the need for Influenza A virus (IAV) surveillance is rising. The gold standard procedure for detecting IAV is to sample acutely diseased pigs. Endemic infections with unspecific clinical signs and low disease prevalence need new approaches. Our study aimed to evaluate a standardized sampling procedure for the detection of IAV in epidemically and endemically infected farms. We performed a cross-sectional study in 131 farms investigating three different age groups per farm in 12 European countries. The results of our investigation indicate that 10 nasal swabs each in suckling piglets, weaners and middle of nursery is a valuable tool for influenza detection and identification of subtypes. However, for farms with a lower prevalence than 15% it is advisable to either increase the number of nasal swabs in each age group or to use group sampling methods. Interestingly, different subtypes were found in different age groups. Thus, our study underlines that sampling of different age groups is mandatory to obtain a comprehensive overview on all circulating variants on farm. In addition, our results highlight that sampling strategies should also consider piglets without obvious clinical signs for IAV infection.

Abstract

Swine influenza A virus (swIAV), which plays a major role in the porcine respiratory disease complex (PRDC), is eliminated from the respiratory tract within 7–9 days after infection. Therefore, diagnosis is complicated in endemically infected swine herds presenting no obvious clinical signs. This study aimed to investigate the right time point for sampling to detect swIAV. A cross-sectional study was performed in 131 farms from 12 European countries. The sampling protocol included suckling piglets, weaners, and nursery pigs. In each age group, 10 nasal swabs were collected and further examined in pools of 5 for swIAV by Matrix rRT-PCR, followed by a multiplex RT-PCR to determine the influenza subtype. SwIAV was detected in 284 (37.9%) of the samples and on 103 (78.6%) farms. Despite the highest number of animals with clinical signs being found in the nursery, the weaners were significantly more often virus-positive compared to nursery pigs (p = 0.048). Overall, the swIAV detection rate did not significantly differ between diseased or non-diseased suckling and nursery piglets, respectively; however, diseased weaners had significantly more positive pools than the non-diseased animals. Interestingly, in 9 farms, different subtypes were detected in different age groups. Our findings indicate that to detect all circulating swIAV subtypes on a farm, different age groups should be sampled. Additionally, the sampling strategy should also aim to include non-diseased animals, especially in the suckling period.