Development of a biosecurity assessment tool in Japanese commercial swine farms

Prev Vet Med. 2019 Nov 15;175:104848. doi: 10.1016/j.prevetmed.2019.104848. [Epub ahead of print]

Development of a biosecurity assessment tool and the assessment of biosecurity levels by this tool on Japanese commercial swine farms.

Sasaki Y1, Furutani A2, Furuichi T3, Hayakawa Y4, Ishizeki S5, Kano R6, Koike F7, Miyashita M8, Mizukami Y9, Watanabe Y5, Otake S10; P-JET11.

Author information

1

Department of Animal and Grassland Sciences, Faculty of Agriculture, University of Miyazaki, Miyazaki, Japan; Center for Animal Disease Control, University of Miyazaki, Miyazaki, Japan. Electronic address: yskssk@cc.miyazaki-u.ac.jp.

2

Course of Animal and Grassland Sciences, Graduate School of Agriculture, University of Miyazaki, Miyazaki, Japan.

3

Feed One Co., Ltd., Kanagawa, Japan.

4

IDEAS Swine Clinic, Chiba, Japan.

5

Summit Veterinary Services, Gunma, Japan.

6

Boehringer Ingelheim Animal Health Japan Co. Ltd., Tokyo, Japan.

7

SMC Co., Ltd., Kanagawa, Japan.

8

Eckstein Swine Service, Tokyo, Japan.

9

Akabane Animal Clinic, Aichi, Japan.

10

Swine Extension & Consulting, Inc., Niigata, Japan.

11

PRRS-Japan Elimination Team, Tokyo, Japan.

Abstract

It is well known that infectious diseases such as porcine reproductive and respiratory syndrome (PRRS) and porcine epidemic diarrhea (PED) decrease herd productivity and lead to economic loss. It is believed that biosecurity practices are effective for the prevention and control of such infectious diseases. Therefore, the objective of the present study was to investigate whether or not an association between biosecurity level and herd productivity, as well as disease status exists on Japanese commercial swine farms. The present study was conducted on 141 farms. Biosecurity in each farm was assessed by a biosecurity assessment tool named BioAsseT. BioAsseT has a full score of 100 and consists of three sections (external biosecurity, internal biosecurity and diagnostic monitoring). Production data for number of pigs weaned per sow per year (PWSY) and post-weaning mortality per year (PWM) were collected for data analysis. Regarding PRRS status, the farms were categorized into two groups: unknown or unstable and stable or negative. In addition, these farms were categorized based on their PED status, either positive or negative. The total BioAsseT score was associated with herd productivity: as total score increased by 1, PWSY increased by 0.104 pigs and PWM decreased by 0.051 % (P <  0.05). Herd productivity was associated with the score of external and internal biosecurity (P <  0.05), but did not correlate with the score of diagnostic monitoring. Regarding PRRS status, farms with an unknown or unstable status had lower total score than those with stable or negative status (P < 0.05). Similarly, PED positive farms had a lower total score compared to PED negative farms (P <  0.05). In conclusion, the present study provides evidence for the association between high biosecurity levels and increased herd productivity as well as a decreased risk for novel introductions of infectious diseases such as PED.

Copyright © 2019 Elsevier B.V. All rights reserved.

KEYWORDS: 

Biosecurity practice; Herd management; Porcine epidemic diarrhea; Porcine reproductive and respiratory syndrome; Sow

PMID:

 

31786401

  

DOI:

 

10.1016/j.prevetmed.2019.104848

Recombination of vaccine and field strains

Emerg Infect Dis. 2019 Dec;25(12):2335-2337. doi: 10.3201/eid2512.191111.

Recombination between Vaccine and Field Strains of Porcine Reproductive and Respiratory Syndrome Virus.

Wang A, Chen Q, Wang L, Madson D, Harmon K, Gauger P, Zhang J, Li G.

Abstract

We isolated and plaque purified IA76950-WT and IA70388-R, 2 porcine reproductive and respiratory syndrome viruses from pigs in the same herd in Iowa, USA, that exhibited coughing and had interstitial pneumonia. Phylogenetic and molecular evolutionary analysis indicated that IA70388-R is a natural recombinant from Fostera PRRSV vaccine and field strain IA76950-WT.

KEYWORDS: 

PRRSV; United States; pigs; porcine reproductive and respiratory syndrome virus; recombination; swine; vaccine; viruses; wild type

PMID:

 

31742529

  

DOI:

 

10.3201/eid2512.191111

Macroepidemiological aspects of PRRSV detection by major labs in the USA over time, age group, and specimen

PLoS One. 2019 Oct 16;14(10):e0223544. doi: 10.1371/journal.pone.0223544. eCollection 2019.

Macroepidemiological aspects of porcine reproductive and respiratory syndrome virus detection by major United States veterinary diagnostic laboratories over time, age group, and specimen.

Trevisan G1, Linhares LCM1, Crim B1, Dubey P1, Schwartz KJ1, Burrough ER1, Main RG1, Sundberg P2, Thurn M3, Lages PTF3, Corzo CA3, Torrison J3, Henningson J4, Herrman E4, Hanzlicek GA4, Raghavan R4, Marthaler D4, Greseth J5, Clement T5, Christopher-Hennings J5, Linhares DCL1.

Author information

1

Veterinary Diagnostic and Production Animal Medicine, Iowa State University, Ames, Iowa, United States of America.

2

Swine Health Information Center, Ames, Iowa, United States of America.

3

Veterinary Population Medicine, University of Minnesota, Saint Paul, Minnesota, United States of America.

4

College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America.

5

Veterinary & Biomedical Sciences Department, South Dakota State University, Brookings, South Dakota, United States of America.

Abstract

This project investigates the macroepidemiological aspects of porcine reproductive and respiratory syndrome virus (PRRSV) RNA detection by veterinary diagnostic laboratories (VDLs) for the period 2007 through 2018. Standardized submission data and PRRSV real-time reverse-transcriptase polymerase chain reaction (RT-qPCR) test results from porcine samples were retrieved from four VDLs representing 95% of all swine samples tested in NAHLN laboratories in the US. Anonymized data were retrieved and organized at the case level using SAS (SAS® Version 9.4, SAS® Institute, Inc., Cary, NC) with the use of PROC DATA, PROC MERGE, and PROC SQL scripts. The final aggregated and anonymized dataset comprised of 547,873 unique cases was uploaded to Power Business Intelligence-Power BI® (Microsoft Corporation, Redmond, Washington) to construct dynamic charts. The number of cases tested for PRRSV doubled from 2010 to 2018, with that increase mainly driven by samples typically used for monitoring purposes rather than diagnosis of disease. Apparent seasonal trends for the frequency of PRRSV detection were consistently observed with a higher percentage of positive cases occurring during fall or winter months and lower during summer months, perhaps due to increased testing associated with well-known seasonal occurrence of swine respiratory disease. PRRSV type 2, also known as North American genotype, accounted for 94.76% of all positive cases and was distributed across the US. PRRSV type 1, also known as European genotype, was geographically restricted and accounted for 2.15% of all positive cases. Co-detection of both strains accounted for 3.09% of the positive cases. Both oral fluid and processing fluid samples, had a rapid increase in the number of submissions soon after they were described in 2008 and 2017, respectively, suggesting rapid adoption of these specimens by the US swine industry for PRRSV monitoring in swine populations. As part of this project, a bio-informatics tool defined as Swine Disease Reporting System (SDRS) was developed. This tool has real-time capability to inform the US swine industry on the macroepidemiological aspects of PRRSV detection, and is easily adaptable for other analytes relevant to the swine industry.

PMID:

 

31618236

  

DOI:

 

10.1371/journal.pone.0223544

Assessing PRRSv status in suckling pigs by sampling sows and environment.

Vet Microbiol. 2019 Oct;237:108406. doi: 10.1016/j.vetmic.2019.108406. Epub 2019 Sep 3.

Indirect assessment of porcine reproductive and respiratory syndrome virus status in pigs prior to weaning by sampling sows and the environment.

Vilalta C1, Sanhueza J2, Garrido J2, Murray D3, Morrison R2, Corzo CA2, Torremorell M2.

Author information

Abstract

There is a need to develop cost effective approaches to sample large populations in particular to determine the disease status of pigs prior to weaning. In this study we assessed the presence of the porcine reproductive and respiratory syndrome virus (PRRSV) in the environment (surfaces and air) of farrowing rooms, and udder skin of lactating sows as an indirect measure of piglet PRRSV status. Samples were collected at processing and weaning every three weeks for 23 weeks after a PRRSV outbreak was diagnosed in a swine breeding herd. PRRSV was detected at processing in udder skin wipes, environmental wipes and airborne deposited particle samples up to 14 weeks post outbreak and at weaning in udder skin wipes up to 17 weeks post outbreak. Similar sensitivities were observed for udder skin wipes (43% [95% CI: 23%-66%]) and surface wipes (57% [95% CI: 34%-77%]) when compared to serum at the litter level from piglets at processing. PRRSV was detected in the environment and the udder skin of lactating sows, which indicates that aggregate samples of the environment or lactating sows may be used to evaluate the PRRSV status of the herd in pigs prior to weaning. However, the use of environmental samples to detect PRRSV by RT-PCR should not be used as the single method to assess the PRRSV status at the litter level. Furthermore, our findings also highlight potential sources of PRRSV infection for piglets in breeding herds.

Copyright © 2019 Elsevier B.V. All rights reserved.

KEYWORDS: 

Environment; Monitoring; Nurse sow; PRRSV; Udder

PMID:

 

31585654

 

DOI:

 

10.1016/j.vetmic.2019.108406

PLoS One. 2019 Oct 9;14(10):e0223250. doi: 10.1371/journal.pone.0223250. eCollection 2019.

Unweaving tangled mortality and antibiotic consumption data to detect disease outbreaks - Peaks, growths, and foresight in swine production.

Lopes Antunes AC1, Jensen VF1, Jensen D2.

Author information

1

Division for Diagnostics & Scientific Advice-Epidemiology, National Veterinary Institute/Centre for Diagnostics-Technical University of Denmark, Lyngby, Denmark.

2

Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg C, Denmark.

Abstract

As our capacity to collect and store health data is increasing, a new challenge of transforming data into meaningful information for disease monitoring and surveillance has arisen. The aim of this study was to explore the potential of using livestock mortality and antibiotic consumption data as a proxy for detecting disease outbreaks at herd level. Changes in the monthly records of mortality and antibiotic consumption were monitored in Danish swine herds that became positive for porcine reproductive and respiratory syndrome (PRRS) and porcine pleuropneumonia. Laboratory serological results were used to identify herds that changed from a negative to a positive status for the diseases. A dynamic linear model with a linear growth component was used to model the data. Alarms about state changes were raised based on forecast errors, changes in the growth component, and the values of the retrospectively smoothed values of the growth component. In all cases, the alarms were defined based on credible intervals and assessed prior and after herds got a positive disease status. The number of herds with alarms based on mortality increased by 3% in the 3 months prior to laboratory confirmation of PRRS-positive herds (Se = 0.47). A 22% rise in the number of weaner herds with alarms based on the consumption of antibiotics for respiratory diseases was found 1 month prior to these herds becoming PRRS-positive (Se = 0.22). For porcine pleuropneumonia-positive herds, a 10% increase in antibiotic consumption for respiratory diseases in sow herds was seen 1 month prior to a positive result (Se = 0.5). Monitoring changes in mortality data and antibiotic consumption showed changes at herd level prior to and in the same month as confirmation from diagnostic tests. These results also show a potential value for using these data streams as part of surveillance strategies.

PMID:

 

31596880

 

DOI:

 

10.1371/journal.pone.0223250

Using commercial ELISAs to assess humoral response in sows repeatedly vaccinated with MLV PRRSV.

Vet Rec. 2019 Oct 1. pii: vetrec-2019-105432. doi: 10.1136/vr.105432. [Epub ahead of print]

Using commercial ELISAs to assess humoral response in sows repeatedly vaccinated with modified live porcine reproductive and respiratory syndrome virus.

Díaz I1, Genís-Jorquera B2, Martín-Valls GE3, Mateu E2,3.

Author information

1

IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Bellaterra, Spain ivan.diaz@irta.es.

2

IRTA, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Bellaterra, Spain.

3

Departament de Sanitat i Anatomia Animals, Facultat Veterinària, Universitat Autònoma de Barcelona, Bellaterra, Spain.

Abstract

BACKGROUND: 

Sows in breeding herds are often mass vaccinated against porcine reproductive and respiratory syndrome (PRRS) every few months using modified live vaccines (MLV). Field veterinarians repeatedly report that multiple vaccinated sows test negative in ELISA. Obviously, this creates uncertainty when assessing the compliance of vaccination and the status of sows.

METHODS: 

In the present study, four commercial ELISAs were used to assess the serological PRRS status in gilts and sows of three farms that were PRRS MLV vaccinated every four months. Animals were tested before vaccination (BV) and postvaccination (PV). Total and neutralising antibodies and cell-mediated responses were also measured in animals that yielded negative results in all ELISAs.

RESULTS: 

The proportion of seronegative animals BV varied depending on the farm and the ELISA used. When samples were analysed using only one ELISA, a substantial number of negative results obtained BV remained as negative afterwards. Five animals were negative BV and PV with all the examined ELISAs. Those animals also yielded negative results in all the other immunological assays.

CONCLUSION: 

Our findings suggest that the use of ELISA for monitoring multiple PRRS MLV vaccinated sows is very limited due to the variability of the humoral responses and the moderate agreement between tests.

© British Veterinary Association 2019. No commercial re-use. See rights and permissions. Published by BMJ.

KEYWORDS: 

Diagnostics; ELISA; Porcine reproductive and respiratory syndrome (PRRS); Vaccines

PMID:

 

31575761

 

DOI:

 

10.1136/vr.105432

Machine-learning algorithms to identify key biosecurity practices and factors associated with breeding herds reporting PRRS outbreak

Author links open overlay panelGustavo S.Silvaa1GustavoMachadob1Kimberlee L.BakeraDerald J.HoltkampaDaniel C.L.Linharesa

a

Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Ames, Iowa, United States

b

Department of Population Health and Pathobiology, North Carolina State University, College of Veterinary Medicine, Raleigh, North Carolina, United States

Received 5 April 2019, Revised 12 August 2019, Accepted 19 August 2019, Available online 20 August 2019.

https://doi.org/10.1016/j.prevetmed.2019.104749Get rights and content

Abstract

Investments in biosecurity practices are made by producers to reduce the likelihood of introducing pathogens such as porcine reproductive and respiratory syndrome virus (PRRSv). The assessment of biosecurity practices in breeding herds is usually done through surveys. The objective of this study was to evaluate the use of machine-learning (ML) algorithms to identify key biosecurity practices and factors associated with breeding herds self-reporting (yes or no) a PRRS outbreak in the past 5 years. In addition, we explored the use of the positive predictive value (PPV) of these models as an indicator of risk for PRRSv introduction by comparing PPV and the frequency of PRRS outbreaks reported by the herds in the last 5 years. Data from a case control study that assessed biosecurity practices and factors using a survey in 84 breeding herds in U.S. from 14 production systems were used. Two methods were developed, method A identified 20 variables and accurately classified farms that had reported a PRRS outbreak in the previous 5 years 76% of the time. Method B identified six variables which 5 of these had already been selected by model A, although model B outperformed the former model with an accuracy of 80%. Selected variables were related to the frequency of risk events in the farm, swine density around the farm, farm characteristics, and operational connections to other farms. The PPVs for methods A and B were highly correlated to the frequency of PRRSv outbreaks reported by the farms in the last 5 years (Pearson r = 0.71 and 0.77, respectively). Our proposed methodology has the potential to facilitate producer’s and veterinarian’s decisions while enhancing biosecurity, benchmarking key biosecurity practices and factors, identifying sites at relatively higher risk of PRRSv introduction to better manage the risk of pathogen introduction.

Keywords

biosecurity practices and factors

PRRSv outbreaks

risk index

machine learning

decision-making

Processing fluids for longitudinal monitoring of PRRSV in herds undergoing virus elimination

Porcine Health Manag. 2019 Aug 1;5:18. doi: 10.1186/s40813-019-0125-x. eCollection 2019.

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

Trevisan G1, Jablonski E2, Angulo J2, Lopez WA1, Linhares DCL1.

Author information

1

1Veterinary Diagnostic and Production Animal Medicine, Iowa State University, Ames, Iowa USA.

2

2Zoetis, Parsippany, New Jersey USA.

Abstract

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.

KEYWORDS: 

Herd closure; Porcine reproductive and respiratory syndrome virus; Processing fluid; Time to stability

PMID:

 

31388438

 

PMCID:

 

PMC6670174

 

DOI:

 

10.1186/s40813-019-0125-x

Free PMC Article

Aerosol Detection and Transmission of PRRSV: What Is the Evidence, and What Are the Knowledge Gaps?

Viruses. 2019 Aug 3;11(8). pii: E712. doi: 10.3390/v11080712.

Aerosol Detection and Transmission of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV): What Is the Evidence, and What Are the Knowledge Gaps?

Arruda AG1, Tousignant S2, Sanhueza J3, Vilalta C3, Poljak Z4, Torremorell M3, Alonso C5, Corzo CA3.

Author information

Abstract

In human and veterinary medicine, there have been multiple reports of pathogens being airborne under experimental and field conditions, highlighting the importance of this transmission route. These studies shed light on different aspects related to airborne transmission such as the capability of pathogens becoming airborne, the ability of pathogens to remain infectious while airborne, the role played by environmental conditions in pathogen dissemination, and pathogen strain as an interfering factor in airborne transmission. Data showing that airborne pathogens originating from an infectious individual or population can infect susceptible hosts are scarce, especially under field conditions. Furthermore, even though disease outbreak investigations have generated important information identifying potential ports of entry of pathogens into populations, these investigations do not necessarily yield clear answers on mechanisms by which pathogens have been introduced into populations. In swine, the aerosol transmission route gained popularity during the late 1990's as suspicions of airborne transmission of porcine reproductive and respiratory syndrome virus (PRRSV) were growing. Several studies were conducted within the last 15 years contributing to the understanding of this transmission route; however, questions still remain. This paper reviews the current knowledge and identifies knowledge gaps related to PRRSV airborne transmission.

KEYWORDS: 

aerosol; airborne; porcine reproductive and respiratory syndrome; porcine reproductive and respiratory syndrome virus (PRRSV); transmission

PMID:

 

31382628

 

DOI:

 

10.3390/v11080712

Front Vet Sci. 2019 Jun 21;6:194. doi: 10.3389/fvets.2019.00194. eCollection 2019.

Individual or Common Good? Voluntary Data Sharing to Inform Disease Surveillance Systems in Food Animals.

Perez AM1, Linhares DCL2, Arruda AG3, VanderWaal K1, Machado G4, Vilalta C1, Sanhueza JM1, Torrison J1, Torremorell M1, Corzo CA1.

Author information

Abstract

Livestock producers have traditionally been reluctant to share information related to their business, including data on health status of their animals, which, sometimes, has impaired the ability to implement surveillance programs. However, during the last decade, swine producers in the United States (US) and other countries have voluntarily begun to share data for the control and elimination of specific infectious diseases, such as the porcine reproductive and respiratory syndrome virus (PRRSv). Those surveillance programs have played a pivotal role in bringing producers and veterinarians together for the benefit of the industry. Examples of situations in which producers have decided to voluntarily share data for extended periods of time to support applied research and, ultimately, disease control in the absence of a regulatory framework have rarely been documented in the peer-reviewed literature. Here, we provide evidence of a national program for voluntary sharing of disease status data that has helped the implementation of surveillance activities that, ultimately, allowed the generation of critically important scientific information to better support disease control activities. Altogether, this effort has supported, and is supporting, the design and implementation of prevention and control approaches for the most economically devastating swine disease affecting the US. The program, which has been voluntarily sustained and supported over an extended period of time by the swine industry in the absence of any regulatory framework and that includes data on approximately 50% of the sow population in the US, represents a unique example of a livestock industry self-organized surveillance program to generate scientific-driven solutions for emerging swine health issues in North America.

KEYWORDS: 

US; data sharing; epidemiology; porcine reproductive and respiratory syndrome; surveillance

PMID:

 

31294036

 

PMCID:

 

PMC6598744

 

DOI:

 

10.3389/fvets.2019.00194

Assessment of immediate production impact following attenuated PRRS type 2 virus vaccination in swine breeding herds

• Cesar A. A. Moura,
• Clayton Johnson,
• Samuel R. Baker,
• Derald J. Holtkamp,
• Chong Wang and
• Daniel C. L. LinharesEmail authorView ORCID ID profile

Porcine Health Management20195:13

https://doi.org/10.1186/s40813-019-0120-2

©  The Author(s). 2019

• Received: 6 February 2019
• Accepted: 13 May 2019
• Published: 11 June 2019

Abstract

Background

To mitigate production impact of porcine reproductive and respiratory syndrome (PRRS) virus outbreaks, it has been common to preventively vaccinate swine breeding herds using PRRS modified live virus (MLV) vaccine. However, attenuated PRRS virus (PRRSv) may result negative impact on farm productivity. The objective of this study was to measure the immediate impact of PRRS type 2 MLV vaccine on breeding herd performance under field conditions. Eight PRRS-stable farms routinely mass vaccinating females with commercial PRRS MLV vaccines were enrolled on study. Vaccination dates were collected and weekly changes in abortions, neonatal losses, pre-weaning mortality, pigs weaned per sow, and wean-to-first-service interval were assessed for up to 6 weeks after each vaccination. A 6-week period prior to each vaccination was established as baseline. Statistical process control (SPC) analysis was conducted to detect significant productivity decreases after MLV interventions, on each farm, and a mixed regression model was used, at the aggregated data level, to assess the productivity change 6 weeks after PRRS MLV vaccinations, compared to baseline.

Results

Out of 65 herd-MLV vaccinations, SPC analysis detected increase on abortions 4 times (6.1%), on neonatal losses 7 times (10.7%), on pre-weaning mortality 2 times (3%), on wean-to-first-service interval 2 times (3%), and no change in total pigs weaned. On aggregated data analysis, there was no significant change in abortion rate, neonatal losses, number of pigs weaned per sow, and wean-to-first-service interval. However, there was an increase of 0.26% of pre-weaning mortality 2 weeks after vaccination compared to the baseline.

Conclusions

Under study conditions, individual PRRS-stable sow farms had experienced transient, and numerically small changes in productivity following PRRS type 2 MLV vaccination. There was a small increase of pre-weaning mortality 2 weeks after vaccination, but no evidence of significant production impact at aggregated data analysis for abortion rate, neonatal losses, pigs weaned per sow and wean-to-first-service interval.

Keywords

• Swine
• PRRS
• Vaccination
• MLV
• Outbreak
• Epidemiology