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Porcine reproductive and respiratory syndrome virus (PRRSv) is an economically significant swine pathogen causing production losses in the global swine industry. Clinical impact depends on many factors including the virus itself. One method to sub-type PRRSv is using restriction fragment length polymorphism (RFLP). The RFLP pattern 1-7-4 emerged within the United States swine industry in 2014 and has become prevalent since then. This was a field study that prospectively followed 1-7-4-infected breeding herds (n=107) and compared time to stability (TTS), time to baseline production (TTBP) and total loss per 1000 sows between herds using modified-live virus vaccine (MLV) on sows and gilts (MLV-MLV), MLV on sows and MLV in addition to field virus exposure on gilts (MLV-MLV/FVE) or not deliberately exposing sows or gilts to PRRSv (Natural-Natural). Analyses were done in SAS 9.4 and results were adjusted by selected co-variates (duration of herd closure, number of previous PRRSv outbreaks of last 3 years, weaning frequency/week, gilt development unit location, herd size and production system). Survival analysis was conducted on TTS and TTBP and regression analysis on total loss. Herds in the Natural-Natural group achieved TTS and TTBP before other herds. Herds in the MLV-MLV/FVE had the longest TTS and TTBP. The total loss was numerically least in MLV-MLV herds (1194 pigs/1000 sows) compared to MLV/MLV-FVE (1810/1000 sows) and Natural-Natural (2671/1000 sows). This study provided additional information to assist veterinarians deciding between methods of exposure to manage PRRSv infection from breeding herds., (Copyright © 2017 Elsevier B.V. All rights reserved.)

To control and eliminate porcine reproductive and respiratory syndrome virus (PRRSv) from breeding herds, some veterinarians adopt a strategy called load-close-expose which consists of interrupting replacement pig introduction for several months and exposing the pigs to a replicating PRRSv. This was a prospective quasi-experiment that followed 61 breeding herds acutely infected with PRRSv that adopted one of two exposure programs: modified-live virus (MLV) vaccine or live-resident virus inoculation (LVI). Treatment groups (load-close-expose with MLV or LVI) were compared for: (a) time-to-PRRSv stability (TTS), defined as time in weeks it took to produce PRRSv negative pigs at weaning; (b) the time-to-baseline production (TTBP), defined using statistical process control methods to represent time to recover to the number of pigs weaned per week that herds had prior to PRRSv-detection; and (c) the total production loss in terms of number of pigs weaned per week. TTS and TTBP were compared between treatments using survival analysis. Day 1 of the program was considered to be the day that treatment was administered. Sampling at herds consisted of bleeding 30 due-to-wean piglets on a monthly basis. Serum was tested for PRRSv RNA by RT-PCR. Herds in which PRRSv was not detected over a 90-day period were classified as reaching stability. Multivariate analysis using proportional hazards regression was performed adjusting the effect of treatment on TTBP and TTS to 'severity of PRRSv infection', 'number of whole-herd exposures', 'days from PRRSv-detection to intervention', 'prior PRRSv-infection status' and 'veterinary clinic associated with the herd'. Total loss was compared between groups using multivariate regression analysis adjusted by selected covariates. The median TTS among participating herds was 26.6 weeks (25th to 75th percentile, 21.6-33.0 weeks). The overall TTBP was 16.5 weeks (range 0-29 weeks). The magnitude of production losses following whole-herd exposure averaged 2217 pigs not weaned/1000 sows and was correlated with TTBP. Herds in the MLV group recovered production sooner and had less total loss than herds in the LVI group. TTBP and TTS were significantly shorter and the total loss was significantly less in herds assisted by a specific veterinary clinic and herds that were infected with PRRSv in the 3 years prior to the study. This study provided new metrics to assist veterinarians to decide between methods of exposure to control and eliminate PRRSv from breeding herds., (Copyright © 2014 Elsevier B.V. All rights reserved.)

We compared 3 modified-live pseudorabies virus (PRV) vaccine strains, administered by the intranasal (IN) or IM routes to 4- to 6-week-old pigs, to determine the effect of high- and low-challenge doses in these vaccinated pigs. At the time of vaccination, all pigs had passively acquired antibodies to PRV. Four experiments were conducted. Four weeks after vaccination, pigs were challenge-exposed IN with virulent virus strain Iowa S62. In experiments 1 and 2, a high challenge exposure dose (10(5.3) TCID50) was used, whereas in experiments 3 and 4, a lower challenge exposure dose (10(2.8) TCID50) was used. This low dose was believed to better simulate field conditions. After challenge exposure, pigs were evaluated for clinical signs of disease, weight gain, serologic response, and viral shedding. When vaccinated pigs were challenge-exposed with a high dose of PRV, the duration of viral shedding was significantly (P less than 0.05) lower, and body weight gain was greater in vaccinated pigs, compared with nonvaccinated challenge-exposed pigs. Pigs vaccinated IN shed PRV for fewer days than pigs vaccinated IM, but this difference was not significant. When vaccinated pigs were challenge-exposed with a low dose, significantly (P less than 0.05) fewer pigs vaccinated IN (51%) shed PRV, compared with pigs vaccinated IM (77%), or nonvaccinated pigs (94%). Additionally, the duration of viral shedding was significantly (P less than 0.05) shorter in pigs vaccinated IN, compared with pigs vaccinated IM or nonvaccinated pigs. The high challenge exposure dose of PRV may have overwhelmed the local immune response and diminished the advantages of the IN route of vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of an ELISA that can differentiate between swine infected with pseudorabies virus (PRV) and swine vaccinated with a specific PRV vaccine was evaluated on an individual and herd basis, and a system for interpreting ELISA results on a herd basis was developed. In 17 herds, recently introduced replacement gilts, seronegative for PRV, were vaccinated with a thymidine kinase- and glycoprotein X (gpX)-deleted vaccine. After vaccination, blood samples were collected from these gilts approximately every 1 to 2 months for up to 19 months. Serum samples were analyzed for antibodies to gpX antigen, using a commercially available ELISA kit according to the manufacturer's protocol. Herd status was determined as positive, suspect, or negative, according to the serum sample:negative control (S:N) values of the samples collected from the herd. From the 17 herds, 130 evaluations were performed. On 49 (38%) of the 130 herd evaluations, 1 or more gilts had suspect test results. Additional testing was required in 19 (39%) of these 49 herd evaluations to determine the PRV infection status of the herd. Status of herds having gilts with suspect results and no positive results was usually negative after retesting. Herds having gilts with positive results were unlikely to have negative status after retesting.

In theory, pseudorabies virus (PRV) may be eliminated from any size of breeding herd by phased test and removal if replacement gilts are not infected with PRV, culling decisions are partially based on PRV status, and the cull rate is higher than the incidence rate of PRV. Annual cull rates are commonly at least 50%, but little information exists on the incidence of PRV within enzootically infected swine herds. The purpose of this study was to develop a method by which spread of PRV could be detected among breeding swine within enzootically infected herds and to determine the incidence of PRV infection in these herds. Data were collected from 17 herds that were quarantined for PRV and ranged in size from 120 to 1,100 sows. At each herd, within the first 5 days of introduction, a group of approximately 30 replacement gilts was identified, vaccinated with a glycoprotein X-deleted PRV vaccine, and blood sample was collected. The owner of 1 herd had a nonvaccinated breeding herd and elected to leave incoming gilts nonvaccinated. After vaccination, blood samples were collected every 1 to 2 months for an average of 13.6 months. Serum samples from vaccinated gilts were tested for antiglycoprotein X antibodies by a specific differential ELISA. Samples from nonvaccinated gilts were evaluated by serum neutralization test. Product-limit method was used to estimate the probability of not becoming infected with PRV. Spread was detected in 7 of 8 herds that had more than 400 sows and in 2 of 9 herds that had less than 400 sows.(ABSTRACT TRUNCATED AT 250 WORDS)

This study assessed whether recently weaned piglets with maternally derived antibodies were able to generate infectious influenza aerosols. Three groups of piglets were assembled based on the vaccination status of the dam. Sows were either non-vaccinated (CTRL) or vaccinated with the same (VAC-HOM) strain or a different (VAC-HET) strain to the one used for challenge. Piglets acquired the maternally derived antibodies by directly suckling colostrum from their respective dams. At weaning, pigs were challenged with influenza virus by direct contact with an infected pig (seeder pig) and clinical signs evaluated. Air samples, collected using a liquid cyclonic air collector, and individual nasal swabs were collected daily for 10 days from each group and tested by matrix real-time reverse transcriptase polymerase chain reaction (RRT-PCR) assay. Virus isolation and titration were attempted for air samples on Madin-Darby canine kidney cells. All individual pigs from both VAC-HET and CTRL groups tested positive during the study but only one pig in the VAC-HOM group was positive by nasal swab RRT-PCR. Influenza virus could not be detected or isolated from air samples from the VAC-HOM group. Influenza A virus was isolated from 3.2% and 6.4% air samples from both the VAC-HET and CTRL groups, respectively. Positive RRT-PCR air samples were only detected in VAC-HET and CTRL groups on day 7 post-exposure. Overall, this study provides evidence that recently weaned pigs with maternally derived immunity without obvious clinical signs of influenza infection can generate influenza infectious aerosols which is relevant to the transmission and the ecology of influenza virus in pigs. [ABSTRACT FROM AUTHOR]

Summary The control and elimination of porcine reproductive and respiratory syndrome virus (PRRSV) represent two of the most challenging tasks facing the pig industry worldwide. Several factors related to the biology of the virus make disease detection and elimination difficult. Efforts are further hampered by the lack of vaccines that can protect naïve herds from infection. With this in mind, elimination efforts are being initiated which incorporate existing tools and knowledge. A new approach extends herd control strategies to the level of a region. One example of success in PRRSV regional elimination is the Stevens County project in Minnesota. [ABSTRACT FROM AUTHOR]