Porcine Reproductive And Respiratory Syndrome Virus Elimination Research Articles

Breeding for disease resistance is an effective way to solve PRRSV

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is one of the major diseases restricting the development of large-scale pig breeding industry, which has brought huge economic losses to pig industry. Although a lot of work has been done in vaccine development, biosafety and pig health, PRRSV is characterized by easy mutation and recombination of genome, immunosuppression, enhanced antibody dependence, persistent infection, etc., making the prevention, control and elimination of PRRSV very difficult. With the deepening of PRRSV research, it is gradually realized that screening and identifying PRRSV susceptibility/resistance genes and implementing PRRSV disease resistance breeding are long-term and effective strategies for fundamental prevention and control, which has important practical significance for the prevention and control of pig herds.

Rapid genotyping of porcine reproductive and respiratory syndrome virus (PRRSV) using MinION nanopore sequencing.

The global distribution and constant evolution are challenges for the control of porcine reproductive and respiratory syndrome virus (PRRSV), one of the most important viruses affecting swine worldwide. Effective control of PRRSV benefits from genotyping, which currently relies on Sanger sequencing. Here we developed and optimized procedures for real-time genotyping and whole genome sequencing of PRRSV directly from clinical samples based on targeted amplicon- and long amplicon tiling sequencing using the MinION Oxford Nanopore platform. Procedures were developed and tested on 154 clinical samples (including lung, serum, oral fluid and processing fluid) with RT-PCR Ct values ranging from 15 to 35. The targeted amplicon sequencing (TAS) approach was developed to obtain sequences of the complete ORF5 (main target gene for PRRSV genotyping) and partial ORF4 and ORF6 sequences of both PRRSV-1 and PRRSV-2 species. After only 5 min of sequencing, PRRSV consensus sequences with identities to reference sequences above 99% were obtained, enabling rapid identification and genotyping of clinical PRRSV samples into lineages 1, 5 and 8. The long amplicon tiling sequencing (LATS) approach targets type 2 PRRSV, the most prevalent viral species in the U.S. and China. Complete PRRSV genomes were obtained within the first hour of sequencing for samples with Ct values below 24.9. Ninety-two whole genome sequences were obtained using the LATS procedure. Fifty out of 60 sera (83.3%) and 18 out of 20 lung samples (90%) had at least 80% of genome covered at a minimum of 20X sequence depth per position. The procedures developed and optimized in this study here are valuable tools with potential for field application during PRRSV elimination programs.

Time Farms Stay Naïve for Porcine Reproductive and Respiratory Syndrome.

Hesitation on eliminating Porcine Reproductive and Respiratory Syndrome virus (PRRSV) from breeding herds exists since it is difficult to predict how long the herd will remain virus-free. We aimed to estimate the time that breeding herds remained virus-free (naïve) after PRRSV elimination was achieved. Production systems voluntarily shared their breeding herds' health status weekly between July 2009 and October 2021. PRRSV incidence rate and the total number of days a breeding herd remained virus-free were estimated. A total of 221 (17%) herds reached the naïve status 273 times. The median time sites remained in this status was approximately two years. The overall PRRS incidence rate after sites achieved a naïve status was 23.43 PRRS outbreaks per 100 farm years. Estimates obtained here provide insights on how frequently and for how long sites remain naïve, which contribute to informing management practices for PRRS control.

Porcine reproductive and respiratory syndrome control in Saxony and Thuringia - Results of 2 voluntary regional programmes in the years 2011-2018

The present study is intended to show the progress of voluntary porcine reproductive and respiratory syndrome (PRRS) control programmes in Thuringia and Saxony as well as to emphasize the importance of confirmation testing in the case of positive findings in unsuspicious herds. In order to present the progress of porcine reproductive and respiratory syndrome virus (PRRSV) elimination, the findings for the years 2011-2018 as well as data on the elimination programme, type and size of the farms, and use of PRRS vaccination were compiled. Each herd was assigned an antibody and PCR status for each year in order to analyze the relationship between status and year. Furthermore, the association between status and herd size as well as the use of PRRS vaccination were investigated. The relevance of confirmation testing is shown by the findings of the herds in the years following PRRSV elimination. In the majority of affected farms in Saxony, depopulation/repopulation was performed in order to eliminate PRRSV. In Thuringia, PRRSV elimination was frequently accomplished during ongoing production. A significant reduction of positive antibody and PCR findings was observed in both federal states during the investigation period. Higher antibody and PCR levels were evident in farms using PRRS vaccination. In the years following PRRSV elimination, positive PRRSV antibody findings occurred in individual PRRSV-unsuspicious farms. These were shown to be false-positive by use of confirmation tests. The proportion of PRRSV-positive herds in a region with low pig density can be reduced by voluntary control programmes with the eradication method playing a subordinate role. The use of vaccination against PRRSV or alternative control measures is to be considered carefully. In the case of positive findings in unsuspicious farms, confirmation testing is warranted in order to rule out any ongoing PRRS outbreak as well as to clarify the farm's status. Voluntary PRRS elimination and maintenance of the status of "PRRSV unsuspicious" is possible even when individual herds in the region do not participate in the control programme.

Use of processing fluid samples for longitudinal monitoring of PRRS virus in herds undergoing virus elimination

This was an observational study that prospectively followed 29 breeding herds for 65 weeks in the U.S.A. that became infected with porcine reproductive and respiratory syndrome virus (PRRSv). The herds operated in a four-week batch farrowing system and adopted a load-close-expose strategy using a modified-live virus vaccine to achieve PRRSv stability. The purpose of this study was to describe time to stability (TTS) based on RT-qPCR testing for PRRSv RNA on processing fluid samples in herds undergoing PRRSv elimination, after implementing herd closure and mass exposure to a PRRS modified-live virus (MLV) vaccine. For the purpose of this study, stability was defined as consistently producing PRRSv-negative pigs. Study herds were monitored until two consecutive piglet batches tested PRRSv RT-qPCR negative, then 30 due-to-wean piglet sera from the second batch were tested for PRRSv RNA by RT-qPCR. Once the farm re-opened, sera from incoming naïve gilts were tested for anti-PRRSv antibodies by ELISA at 30- and 60-days post-entry to confirm negative status to PRRSv. Day zero was the day of whole-herd exposure to a commercial PRRS vaccine virus. Twenty-eight of 29 herds (96.55%) achieved TTS within the study period. TTS ranged from 18 to 55 weeks with a median of 27 weeks. Serum from due-to-wean piglets was collected on 28 farms, of which 26 (92.85%) obtained PRRSv RT-qPCR-negative results on the first collection. At the end of the observational period, 16 sow farms successfully re-introduced PRRSv-naïve gilts with no detected serologic response. In conclusion, the median time to achieve TTS in breeding herds being operated in a four-week batch farrowing system undergoing PRRSv elimination using load-close-expose with attenuated virus vaccine was 27 weeks. Also, processing fluid-based monitoring of breeding herds under PRRS elimination was practical and reliable to assess PRRSv stability.

Use of processing fluids and serum samples to characterize porcine reproductive and respiratory syndrome virus dynamics in 3 day-old pigs

Collection of serum samples of pigs at weaning to monitor for porcine reproductive and respiratory syndrome virus (PRRSV) has become a common practice to determine PRRSV herd infection status. Diagnostic sensitivity of this practice is low in herds undergoing PRRSV elimination once prevalence of infection is near zero. Thus, the goal of this study was to characterize the dynamics of PRRSV infection in 3 day-old pigs overtime using serum and serosanguineous fluids obtained as part of castration and tail docking practices (processing fluids (PF)). Secondary goal was to estimate sensitivity and specificity of PF in the 3 day old population. A 6000 breed-to-wean sow herd was monitored every three weeks for 23 weeks after a PRRSV outbreak by collecting both PF and individual serum samples from all pigs in the selected litters. Out of the 77 litters tested, 23 (29.8%) were identified as positive using the PF and the serum samples, with a Cohen’s kappa statistic of 0.81 (95% CI: 0.59–1) between the results obtained in each sample type. The sensitivity and specificity of the PF relative to the results in serum was 87% (95% CI: 66%–97%) and 94% (95% CI: 85%–99%) respectively. The percentage of PRRSV positive litters decreased over time and litters from gilts were more likely to test positive than those from older sows. Overall, the study demonstrates that PF can be a convenient and reliable specimen to monitor PRRSV infection in breeding herds.

Economic Analysis of Immunization Strategies for PRRS Control [corrected

Porcine reproductive and respiratory syndrome virus (PRRSv) is a swine-specific pathogen that causes significant increases in production costs. When a breeding herd becomes infected, in an attempt to hasten control and elimination of PRRSv, some veterinarians have adopted a strategy called load-close-expose which consists of interrupting replacement pig introductions into the herd for several weeks (herd closure) and exposing the whole herd to a replicating PRRSv to boost herd immunity. Either modified-live virus (MLV) vaccine or live field-virus inoculation (FVI) is used. This study consisted of partial budget analyses to compare MLV to FVI as the exposure method of load-close-expose program to control and eliminate PRRSv from infected breeding herds, and secondly to estimate benefit / cost of vaccinating sow herds preventatively. Under the assumptions used in this study, MLV held economic advantage over FVI. However, sensitivity analysis revealed that decreasing margin over variable costs below $ 47.32, or increasing PRRSv-attributed cost above $18.89 or achieving time-to-stability before 25 weeks resulted in advantage of FVI over MLV. Preventive vaccination of sow herds was beneficial when the frequency of PRRSv infection was at least every 2.1 years. The economics of preventative vaccination was minimally affected by cost attributed to field-type PRRSv infection on growing pigs or by the breeding herd productivity level. The models developed and described in this paper provide valuable tools to assist veterinarians in their efforts to control PRRSv.

Evaluating perspectives for PRRS virus elimination from pig dense areas with a risk factor based herd index

Porcine reproductive and respiratory syndrome virus (PRRSV) is wide-spread in pig populations globally. In many regions of Europe with intensive pig production and high herd densities, the virus is endemic and can cause disease and production losses. This fuels discussion about the feasibility and sustainability of virus elimination from larger geographic regions. The implementation of a program aiming at virus elimination for areas with high pig density is unprecedented and its potential success is unknown. The objective of this work was to approach pig population data with a simple method that could support assessing the feasibility of a sustainable regional PRRSV elimination. Based on known risk factors such as pig herd structure and neighborhood conditions, an index characterizing individual herds’ potential for endemic virus circulation and reinfection was designed. This index was subsequently used to compare data of all pig herds in two regions with different pig- and herd-densities in Lower Saxony (North-West Germany) where PRRSV is endemic. Distribution of the indexed herds was displayed using GIS. Clusters of high herd index densities forming potential risk hot spots were identified which could represent key target areas for surveillance and biosecurity measures under a control program aimed at virus elimination. In an additional step, for the study region with the higher pig density (2463 pigs/km2 farmland), the potential distribution of PRRSV-free and non-free herds during the implementation of a national control program aiming at national virus elimination was modeled. Complex herd and trade network structures suggest that PRRSV elimination in regions with intensive pig farming like that of middle Europe would have to involve legal regulation and be accompanied by important trade and animal movement restrictions. The proposed methodology of risk index mapping could be adapted to areas varying in size, herd structure and density. Interpreted in the regional context, this could help to classify the density of risk and to accordingly target resources and measures for elimination.

Risk factors for porcine reproductive and respiratory syndrome virus infection and resulting challenges for effective disease surveillance.

BackgroundThis study aimed to identify risk factors for active porcine reproductive and respiratory syndrome virus (PRRSV) infection at farm level and to assess the probability of an infected farm being detected through passive disease surveillance in England. Data were obtained from a cross-sectional study on 147 farrow-to-finish farms conducted from April 2008 – April 2009. The risk factors for active PRRSV infection were identified using multivariable logistic regression analysis. The surveillance system was evaluated using a stochastic scenario tree model.ResultsEvidence of PRRSV circulation was confirmed on 35.1% (95%CI: 26.8-43.4) of farms in the cross sectional study, with a higher proportion of infected farms in areas with high pig density (more than 15000 pigs within 10 km radius from the farm). Farms were more likely to have active PRRSV infection if they used the live virus vaccine-Porcilis PRRS (OR=7.5, 95%CI: 2.5-22.8), were located in high pig density areas (OR=2.9, 95%CI: 1.0-8.3) or had dead pigs collected (OR=5.6, 95%CI: 1.7-18.3). Farms that weaned pigs at 28 days of age or later had lower odds of being PRRSV positive compared to those weaning at 21-27 days (OR=0.2, 95%CI: 0.1-0.7). The probability of detecting an infected farm through passive surveillance for disease was low (mode=0.074, 5th and 95th percentiles: 0.067; 0.083 respectively). In particular farms which used live virus vaccine had lower probabilities for detection compared to those which did not.ConclusionsRisk factors identified highlight the importance of biosecurity measures for the incursion of PRRSV infection. The results further indicate that a combined approach of surveillance for infection and disease diagnosis is needed to assist effective control and/or elimination of PRRSV from the pig population.

A PRRS CAP update on the regional control and elimination of PRRSV (2011)

The control and elimination of porcine reproductive and respiratory syndrome virus (PRRSV) represents one of the most challenging tasks facing the swine industry world- wide. Several factors related to the biology of the virus make disease detection and elimination difficult. Efforts are further hampered by a lack of vaccines that can protect naïve herds from infection. With this in mind, elimination efforts that incorporate existing tools and knowledge are being initiated. The principal focus is at the region level. One example of success is the Stevens County project in Minnesota, which has attained a PRRSV-negative status and has been expanded to include all of northern Minnesota.; Swine Day, Manhattan, KS, November 17, 2011

Characterization of the carrier state in porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome (PRRS) virus infection results in clinically normal, but persistently infected animals. An understanding of the carrier state is necessary for prevention, control and/or elimination of PRRS virus. The objective of this experiment was to estimate the proportion of PRRS virus carriers over time and determine which combination of sample and diagnostic assay could most effectively identify persistently infected animals. Sixty 3-week-old pigs were inoculated with PRRS virus ATCC VR-2332 and followed for up to 105 days post-inoculation (PI). Sixty age-matched animals served as uninoculated controls. Samples (serum, peripheral blood leukocytes, oropharyngeal scrapings, tonsil, bronchoalveolar lavage, lung tissue and tracheobronchial lymph nodes) were collected periodically and tested for evidence of PRRS virus infection by virus isolation (VI), swine bioassay and reverse transcriptase-nested polymerase chain reaction (RT-nPCR). The PRRS virus-specific antibody response was monitored with a commercial enzyme-linked immunosorbent assay (ELISA). Overall, PRRS virus was found in 51 of the 59 (84%) necropsied animals by VI or swine bioassay between 63 and 105 days PI, including 10 of the 11 (91%) of animals at day 105 PI. RT-nPCR on oropharyngeal scrapings was the most effective combination of assay and sample for detecting carriers. There was no significant difference in the antibody response of carrier vs. non-carrier animals. Infectious PRRS virus is present in most pigs the first 105 days following infection. Antibody response, as measured by a commercial ELISA, cannot be used to determine carrier status. RT-nPCR is a useful tool for detection of carriers, but diagnostic sample selection is critical if false negative results are to be avoided.