Economic Analysis of Vaccination Strategies for PRRS Control

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

Porcine reproductive and respiratory syndrome monitoring in breeding herds using processing fluids

Processing fluids (PF), the serosanguinous fluid recovered from piglet castration and tail docking, were used for porcine reproductive and respiratory syndrome virus (PRRSV) infection assessment. Processing fluid samples from four breed-to-wean herds were compared with standard sampling protocols, demonstrating PRRSV RNA detection in PF at greater frequency than standard schemes

Assessment of abattoir based monitoring of PRRSV using oral fluids

Various porcine reproductive and respiratory syndrome virus (PRRSV) regional elimination projects have been implemented in the U.S., but none have yet succeeded. In part, this reflects the need for efficient methods to monitor over time the progress of PRRSV status of participating herds. This study assessed the feasibility of monitoring PRRSV using oral fluids collected at the abattoir. A total of 36 pig lots were included in the study. On-farm oral fluid (n = 10) and serum (n = 10) collected within two days of shipment to the abattoir were used to establish the reference PRRSV status of the population. Oral fluids (n = 3 per lot) were successfully collected from 32 lots (89%) at the lairage. Three veterinary diagnostic laboratories (VDLs) tested the sera (VDL1 and VDL3: n = 316, VDL2: n = 315) and oral fluids (VDL1 and VDL3: n = 319, VDL2: n = 320) for PRRSV antibodies (ELISA) and RNA (rRT-PCR). Environmental samples (n = 64, 32 before and 32 after pigs were placed in lairage) were tested for PRRSV RNA at one VDL. All oral fluids (farm and abattoir) tested positive for PRRSV antibody at all VDLs. PRRSV positivity frequency on serum ranged from 92.4% to 94.6% among VDLs, with an overall agreement of 97.6%. RNA was detected on 1.3% to 1.9%, 8.1% to 17.7%, and 8.3% to 17.7% of sera, on-farm and abattoir oral fluids, respectively. Between-VDLs rRT-PCR agreement on sera and oral fluids (farm and abattoir) ranged from 97.8% to 99.0%, and 79.0% to 81.2%, respectively. Between-locations agreement of oral fluids varied from 31.3% to 50% depending on the VDL. This study reported the application of swine oral fluids collected at the abattoir for monitoring PRRSV, and describes the between-VDL agreement for PRRS testing of serum and oral fluid field samples

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

Systematic review and meta-analysis on efficacy of Fostera PRRSV Modified Live Virus vaccine studies in growing pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important health challenges that currently exists in the global swine industry. PRRSV is an enveloped, single-stranded, positive-sense RNA virus belonging to genus Arterivirus. A PRRSV infection is clinically characterized by reproductive failure in sows and/or respiratory disease in growing pigs, causing significant economic losses (Zimmerman et al., 2012). RNA viruses have relatively high mutation rates compared to DNA viruses, mainly due to the low fidelity of viral RNA-dependent RNA polymerases (Arnold et al., 2005; Vignuzzi et al., 2008). This rapid high mutation rate usually leads to the generation of genetically and antigenically variable virus strains in the field, which can hinder the development of effective vaccines. PRRSV is currently classified into two distinct genotypes, type 1 and type 2 which differs significantly in term of their clinical, and genetic properties (Kapur et al., 1996; Labarque et al., 2004; Nelson et al., 1993). Within type 2, it has been proposed a further subdivision into 9 genetic lineages (Shi et al., 2010). The extensive heterogeneity of PRRSV presents challenges for the efficacy vaccines, which are currently based on a single virus strain. Consequently, the current commercially vaccines confer partial cross-protection against heterologous PRRSV strains (Kimman et al., 2009; Li et al., 2014; Murtaugh and Genzow, 2011), which is sufficient to significantly decrease duration and magnitude of viremia, shedding, and lung lesions. In previous cross-protection studies, type 2 PRRSV modified live vaccine have not been effective when applied to control pigs against type 1 PRRSV (Labarque et al., 2003; van Woensel et al., 1998; Labarque et al., 2000). Cross-protection discoursed by type 2 PRRSV vaccine against type 1 PRRSV is an important clinical issue in many Asian countries because of the emergence of type 1 PRRSV (Chen et al., 2011; Nam et al., 2009; Thanawongnuwech et al., 2004). A modified live type 2 PRRSV vaccine (Fostera PRRS, Zoetis, Parsippany, NJ, USA) was introduced in the US in 2012, and is profess to be efficacious to protect pigs against heterologous type 2 PRRSV challenge (Park et al., 2014), and has been licensed to produce better cross-protection against heterologous PRRSV challenge. Fostera PRRS is an attenuated PRRSV vaccine, passaged first on pig kidney cells engineered to constitutively express the porcine CD163 PRRS receptor, then on baby hamster kidney cells that were also engineered to express porcine CD163. The commercial modified live PRRS vaccines were attenuated by passage on African green monkey kidney cells (cell line MA-104 and derivatives), which inappropriately express the macrophage-specific CD163 PRRS receptor. Adaptation of the virus to use the monkey CD163 receptor contributes to the observed attenuation phenotype of at least some of these vaccines, namely a reduced ability of the vaccine virus to infect the host target cell, primary porcine alveolar macrophages (Pearce et al., 2014). In contrast, the Fostera PRRSv is passaged only on cells expressing porcine CD163, and thus potentially maintaining its ability to replicate to high titer on primary porcine alveolar macrophages. This fundamental difference in attenuation may play a role in the dynamics of viremia in pigs, following challenge with PRRS viruses from genotypes 1 (Charoenchanikran et al., 2016; Choi et al., 2016; Do et al., 2015; Park et al., 2015, 2014; Savard et al., 2016; Tian et al., 2015)

General overview of the detection of Mycoplasma hyopneumoniae DNA by quantitative polymerase chain reaction in diagnostic cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2004 to 2016

Mycoplasma hyopneumoniae (Mhp) is the etiologic agent of enzootic pneumonia and a major causative agent of the porcine respiratory disease complex. This study summarizes and describes the general diagnostic trends on Mhp detection by quantitative polymerase chain reaction (qPCR) in cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2004 to 2016. The following variables were included in the analysis: animal age, geographic location, sample type, season, and submission year. The overall frequency of detection found was 27.04% and ranged from 17.9% to 40.7%. Lung homogenate and bronchial swabs had a greater Mhp qPCR detection rate than other sample types (P \u3c .001) followed by bronchoalveolar lavage (P \u3c .001), while oral fluids had the lowest Mhp detection rate (P \u3c .001). The fall season had a greater percentage of positive Mhp qPCR results when compared to other seasons (P \u3c .001), while spring had the lowest percentage. Finishing-age pigs had a greater percentage of Mhp qPCR detection when compared to other age groups (P \u3c .001), while suckling pigs had the lowest percentage (P \u3c .001)

Comparison of shower-in and shower-in plus bench entry protocols for prevention of environmental contamination due to personnel entry in a commercial swine facility

Objective: To determine if the addition of a bench entry system in a commercial swine facility with a shower lowers the risk of personnel introducing environmental contamination. Materials and methods: Fluorescent powder was used to assess the bench entry system by simulating environmental contamination carried on the footwear of personnel entering a commercial swine farm. On each of ten days, four female employees entered the premises, stepped through the fluorescent powder, performed bench entry procedures, and showered into the farm. For ten additional replicates, the bench was removed and regular farm protocols were followed. The fluorescent powder contamination was evaluated with a grid system at four sampling points including before the bench, after the bench, before the shower, and after the shower. Statistical analysis was conducted to determine if there was a difference in the number of contaminated grid cells found at each sampling between the treatment groups. Results: Fluorescent powder was found after the shower on two study days in which the bench was removed but none when the bench was in place. There was a significant difference in contamination found directly after the bench between days with bench entry and days that the bench was removed, but this was not observed at any of the other sampling points. Implications: A bench entry system may decrease the risk that pathogens reach the clean side of the shower, but improved protocols and additional layers of biosecurity are needed

Evidence of improved reporting of swine vaccination trials in the post-REFLECT statement publication period

Objectives: Describe and compare the proportion of studies reporting the method used to assign study units to treatment groups, reporting a random allocation approach, reporting 18 REFLECT items, and the proportion of studies having a low risk-of-bias assessment in swine vaccination trial studies published after the REFLECT statement, compared to studies published before. Materials and Methods: The study population was 61 studies that evaluated vaccines targeted at pathogens affecting swine health or pork safety. Two reviewers assessed the reporting of 18 of 22 REFLECT items and 5 risk-of-bias domains. Results: Authors reported the method used to allocate experimental units in 33 of 42 (79%) and 14 of 19 (74%) studies published prior to and following REFLECT, respectively. There has been a substantial shift in the reporting of allocation approaches. Before 2011, only 2 of 25 (8%) studies that reported using random allocation provided supporting evidence. This increased in studies published between 2011-2017 (4 of 6; 66%). Before 2011, 8 of 33 (24%) studies reported using systematic allocation, which increased to 43% (6 of 14 studies) between 2011-2017. There has also been an increase in the prevalence of reporting for 14 of the 18 REFLECT items. There was an increase in the number of studies reporting evidence to support true randomization to group and data that suggests few baseline imbalances. Implications: Data from this study suggests swine vaccination trial reporting improved, which may be due to researchers having more access to better quality information

Implementation of PRRSV status classification system in swine breeding herds from a large integrated group in Spain

Background: Porcine Reproductive and Respiratory Syndrome (PRRS) is an endemic swine disease causing significant productive and economic losses. Knowledge of PRRS epidemiology is crucial to develop control strategies against this disease. In that regard, classifying farms according to PRRS virus (PRRSV) shedding and exposure, and understanding key drivers of change in status over time, provides great applied knowledge for developing disease control programs. In most European countries, PRRSV monitoring is performed most frequently at the individual farm level although criteria selected for monitoring varies among different regions and farms. The aim of this study was to implement a systematic monitoring program for PRRSV in Spanish sow farms. Breeding herds were classified according to a standardized PRRSV infection status using sampling programs and terminology currently adopted in the United States (US), which allowed an evaluation of PRRSV epidemiology in a large integrated Spanish group during a one-year study period (February 2017–March 2018). Results: Fifteen farms achieved a stable PRRSV status after the first 4 consecutive samplings and 20 farms were classified as unstable. One of the farms maintained a stable status throughout the duration of the whole monitoring period. Among the 20 farms classified as unstable at the beginning of the monitoring protocol, 9 farms (45%) never reached the stable status and 11 farms (55%) reached stable status afterwards during the monitoring study period. From PRRSV PCR positive pools, there were 47 different PRRSV nucleotide sequences from 24 different farms. More than one PRRSV sequence was obtained from 15 farms. In the farms with more than one sequence detected, we observed recirculation of the same PRRSV field strain in 7 farms and introduction of a different PRRSV strain in 5 farms and both events in 3 farms. Conclusions: Systematic monitoring for PRRSV in breeding herds established a basis of knowledge of PRRSV epidemiology at the farm level and provided key data to classify farms according to PRRSV exposure and shedding status. These data allow further evaluation of the impact of the PRRSV farm status on production and economic performance in breeding herds and additional investigation of factors related to PRRSV epidemiology