Efficient surveillance of pig populations using oral fluids

Abstract

Currently virus surveillance in swine herds is constrained by the cost-effectiveness and efficiency of sampling methods. The objective of this study was to assess the value of using oral fluids collected by barn personnel as a method of surveillance based on PCR testing. Approximately 12,150 pigs in 10 wean-to-finish barns on 10 farms were monitored for the presence of porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV), influenza A virus (IAV), and Torque teno virus genogroups 1 (TTV1) and 2 (TTV2) by sampling oral fluid specimens. Oral fluid samples were collected from 6 pens at each site starting at the time of pig placement (∼3 weeks of age) and continuing thereafter at 2-week intervals for a period of 18 weeks. Data were analyzed both on a pen basis and barn basis. Overall, 508 (85%) samples were positive for PCV2, 73 (12%) for PRRSV, 46 (8%) for IAV, 483 (81%) for TTV2, and 155 (26%) for TTV1 during the study period. The estimated arithmetic means of the quantitative PCR-positive oral fluids for PCV2, PRRSV, and IAV were 1×10(4.62), 1×10(4.97), and 1×10(5.49)per ml. With a single exception, all barns were positive for PCV2 and TTV2 at every sampling point in the study. Virus detection varied among barns, particularly for IAV and PRRSV. The pen level, cumulative distribution of agent combinations between all 10 barns were statistically different. The most commonly observed patterns were PCV2+TTV2 (239 pen samples, 40%), PCV2+TTV1+TTV2 (88 pen samples, 15%), and PCV2 alone (66 pen samples, 11%). This "proof-of-concept" project showed that a variety of viruses could be detected either intermittently or continuously in pig populations and demonstrated that barn herd virus status is highly variable, even among barns in the same production system. Oral fluid sampling is a promising approach for increasing the efficiency and cost effectiveness of virus surveillance in swine herds.

Copyright © 2011 Elsevier B.V. All rights reserved.

Ramirez A, Wang C, Prickett J R, Pogranichniy R, Yoon K, Main R, Johnson J K, Rademacher C, Hoogland M, Hoffmann P, Kurtz A, Kurtz E, Zimmerman J. Efficient surveillance of pig populations using oral fluids. Preventive veterinary medicine 2011 [in press].

Downtime for PRRSv+Myco

Pitkin A, Otake S, Dee S. A one-night downtime period prevents the spread of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae by personnel and fomites (boots and coveralls). J Swine Health Prod. 2011;19(6):345–348.

Summary

This paper summarizes observations recorded over a 4-year (1438-day) period regarding the ability of a 1-night period of downtime [+ shower and cloth-change] to prevent mechanical spread of porcine repro- ductive and respiratory syndrome virus and Mycoplasma hyopneumoniae between pig populations by personnel and fomites.

Keywords: swine, porcine reproductive and respiratory syndrome, downtime, personnel, fomites

Effect of PRRSv vaccine on the shedding of wild-type virus from an infected population of growing pigs

Linhares D C, Cano J P, Wetzell T, Nerem J, Torremorell M, Dee S A. Effect of modified-live porcine reproductive and respiratory syndrome virus (PRRSv) vaccine on the shedding of wild-type virus from an infected population of growing pigs. Vaccine 2011 [in press]

Abstract

There are ongoing efforts to eliminate porcine reproductive and respiratory syndrome virus (PRRSv) from regions in the United States swine industry. However, an important challenge for the accomplishment of those efforts is the re-infection of pig units due to the area spread of PRRSv. The objective of this study was to evaluate the effect of PRRS modified-live virus vaccine (MLV) on viral shedding and on dynamics of PRRSv infection in pig populations raised under commercial conditions. The study composed of two rooms of 1000 pigs each. Ten percent of pigs of each room were inoculated with a field isolate of PRRSv. Rooms had separate air spaces and strict scientifically validated biosecurity protocols were adopted to avoid movement of pathogens between rooms. At 8 and 36dpi (days post inoculation), all pigs of the challenge-vaccine group were inoculated with a MLV vaccine. Pigs of the challenge-control group were placebo-inoculated. Blood and oral fluid samples were collected from each room at 0, 8, 36, 70, 96 and 118dpi for PRRSv RNA detection using PCR. PRRSv-antibodies were also screened from blood serum samples with a commercially available ELISA test. Additionally, tonsil scraping samples were collected from both groups at 70, 96 and 118dpi. Moreover, air samples were collected 6 times per week from 0 to 118dpi and were tested for PRRSv RNA using qPCR assay. There was no difference in the PRRSv infection dynamics measured as duration and magnitude of viremia and seroconversion. Also, there was no difference in the frequency of tonsil scraping samples PRRSv-positive by PCR. However, the challenge-vaccine group had significantly less PRRSv shed compared to the challenge-control group. The challenge-vaccine group had significant less PRRSv-positive oral fluids at 36dpi. Moreover, the challenge-vaccine group had significant reduction in the cumulative PRRSv shed in the air.

Copyright © 2011. Published by Elsevier Ltd.

PMID:

 

22063389

 

[PubMed]

Can we vaccinate pigs via their feed?

Maybe in the near future... see abstract below.

Planta. 2011 Oct 5. [Epub ahead of print]

Expression of the nucleocapsid protein of Porcine Reproductive and Respiratory Syndrome Virus in soybean seed yields an immunogenic antigenic protein.

Vimolmangkang S, Gasic K, Soria-Guerra R, Rosales-Mendoza S, Moreno-Fierros L, Korban SS.

Source

Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL, 61801, USA.

Abstract

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), is a serious disease of swine and contributes to severe worldwide economic losses in swine production. Current vaccines against PRRS rely on the use of an attenuated-live virus; however, these are unreliable. Thus, alternative effective vaccines against PRRS are needed. Plant-based subunit vaccines offer viable, safe, and environmentally friendly alternatives to conventional vaccines. In this study, efforts have been undertaken to develop a soybean-based vaccine against PRRSV. A construct carrying a synthesized PRRSV-ORF7 antigen, nucleocapsid N protein of PRRSV, has been introduced into soybean, Glycine max (L.) Merrill. cvs. Jack and Kunitz, using Agrobacterium-mediated transformation. Transgenic plants carrying the sORF7 transgene have been successfully generated. Molecular analyses of T(0) plants confirmed integration of the transgene and transcription of the PRRSV-ORF7. Presence of a 15-kDa protein in seeds of T(1) transgenic lines was confirmed by Western blot analysis using PRRSV-ORF7 antisera. The amount of the antigenic protein accumulating in seeds of these transgenic lines was up to 0.65% of the total soluble protein (TSP). A significant induction of a specific immune response, both humoral and mucosal, against PRRSV-ORF7 was observed following intragastric immunization of BALB/c female mice with transgenic soybean seeds. These findings provide a 'proof of concept', and serve as a critical step in the development of a subunit plant-based vaccine against PRRS.

A four-year summary of air filtration system efficacy for preventing airborne spread of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae

Summary
A 4-year study evaluated the ability of commercial air filters to protect susceptible populations against airborne transmission
of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneu- moniae. All filter types*, equally reduced the risk of airborne transmission of both pathogens, compared to non-filtered controls, supporting further application in the field.
Keywords: swine, porcine reproductive and respiratory syndrome virus, airborne, trans- mission, filtration



Dee S, Pitkin A, Otake S, et al. A four-year summary of air filtration system efficacy for preventing airborne spread of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae. J Swine Health Prod. 2011;19(5):292–294. 




* types of filters evaluated:
     - mechanical: MERV14 and MERV 16
     - electrostatic
     - chemical

Assessment of Stomoxys calcitrans (Diptera: Muscidae) as a vector of porcine reproductive and respiratory syndrome virus

Abstract

Porcine Reproductive and respiratory syndrome (PRRS) is a globally significant swine disease caused by an arterivirus. The virus replicates in alveolar macrophages of infected pigs, resulting in pneumonia in growing pigs and late-term abortions in sows. Outbreaks occur on disparate farms within an area despite biosecurity measures, suggesting mechanical transport by arthropods. We investigated the vector potential of stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae), in the transmission of porcine reproductive and respiratory syndrome virus (family Arteriviridae, genus Arterivirus, PRRSV) under laboratory conditions. Stable flies were collected around PRRS-negative boar stud barns in North Carolina and tested for presence of the virus. Stable flies were collected on alsynite traps placed near the exhaust fan of the close-sided tunnel-ventilated buildings, suggesting blood seeking flies are attracted by olfactory cues. No flies were positive for PRRSV. We assessed transmission of the virus through an infective bite by feeding laboratory reared stable flies on blood containing virus and transferring them to naive pigs for subsequent bloodmeals. Transmission of the virus to naive pigs by infective bites failed in all attempts. The volume of blood contained within the closed mouthparts of the stable fly seems to be insufficient to deliver an infective dose of the virus. Stable flies are unlikely to transmit PRRSV from one pig to another while blood feeding. The fate of the virus after a bloodmeal remains to be determined.

Rochon K, Baker R B, Almond G W, Watson D W. Assessment of Stomoxys calcitrans (Diptera: Muscidae) as a vector of porcine reproductive and respiratory syndrome virus. Journal of medical entomology 2011;48(4):876-883.

Vet Microbiol. 2011 Jul 1. [Epub ahead of print]

Comparative pathogenicity of type 1 and type 2 isolates of porcine reproductive and respiratory syndrome virus (PRRSV) in a young pig infection model.

Martínez-Lobo FJ, Díez-Fuertes F, Segalés J, García-Artiga C, Simarro I, Castro JM, Prieto C.

Source

Dpto. Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) isolates are classified in two different genotypes, based on genomic heterogeneity: type 1, which comprises European type isolates, and type 2, which includes North American type isolates. It is believed that members of both genotypes differ in some biological properties including pathogenicity, however extensive studies comparing isolates of both genotypes have never been carried out. The objective of the present study was to compare the pathogenic properties of six different PRRSV isolates, three of type 1 and three of type 2, in a young pig infection model. For this purpose, a total of 105 3-week-old piglets were divided in 7 groups of 15 animals that were exposed on day 0 of the experiment to one of the six isolates tested or were mock infected (negative control group). Clinical signs and rectal temperatures were recorded daily and blood samples were taken on days 3, 6, 9, 12, 15, 18 and 21 of the experiment. On days 7, 14 and 21 post-inoculation five animals per group were sacrificed, macroscopic lung lesions were evaluated and different tissue samples were collected to determine viral organic distribution. The results obtained indicate that type 2 isolates are more pneumovirulent than type 1 isolates, as demonstrated by the recording of respiratory clinical signs only in pigs exposed to type 2 viruses and by the severity of macroscopic and microscopic lung lesions in those pigs. However, no clear differences could be established between genotypes in systemic clinical signs or viral load and viral distribution after challenge. These results support the general idea that type 2 isolates induce more severe respiratory disease than type 1 isolates.

Copyright © 2011 Elsevier B.V. All rights reserved.

PMID:

 

21831539

 

[PubMed - as supplied by publisher]

Clin Vaccine Immunol. 2011 Aug 10. [Epub ahead of print]

Effect of the modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine on European and North American PRRSV shedding in semen from infected boars.

Han K, Seo HW, Shin JH, Oh Y, Kang I, Park C, Chae C.

Source

Department of Veterinary Pathology, College of Veterinary Medicine, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea.

Abstract

The objective of the present study was to compare the effects of the modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine (Ingelvac PRRS MLV, Boehringer Ingelheim Animal Health, St. Joseph, MO, USA) on European and North American PRRSV shedding in the semen of experimentally infected boars. The boars were randomly divided into six groups. Vaccinated boars shed the North American PRRSV at the rate of 10(0.1) to 10(1.0) viral genome copies per ml and 3.63 to 10(1.1) 50% tissue culture infective doses (TCID(50))/ml, respectively in semen, whereas non-vaccinated boars shed the North American PRRSV at the rate of 10(0.2) to 10(4.7) viral genome copies per ml and 1.14 to 10(3.07) TCID(50)/ml, respectively in semen. Vaccinated boars shed the European PRRSV at the rate of 10(0.1) to 10(4.57) viral genome copies per ml and 1.66 to 10(3.10) TCID(50)/ml, respectively in semen, whereas non-vaccinated boars shed the European PRRSV at the rate of 10(0.3) to 10(5.14) viral genome copies per ml and 1.69 to 10(3.17) TCID(50)/ml, respectively in semen. The number of genomic copies of the European PRRSV in semen samples was not significantly different between vaccinated and non-vaccinated challenged European PRRSV boars. The present study demonstrated that boar vaccination using commercial modified live PRRSV vaccine was able to decrease subsequent shedding of North American PRRSV in semen after challenge but was unable to decrease shedding of European PRRSV in semen after challenge.

This is not quite an "applied" research, but it is good to know that such technologies are being evaluated and therefore available for "commercial" use soon:

A multiplex method for the simultaneous serological detection of porcine reproductive and respiratory syndrome virus and porcine circovirus type 2.

Lin K, Wang C, Murtaugh MP, Ramamoorthy S.

Source

Department of Veterinary Diagnostic and Production Animal Medicine, Veterinary Diagnostic Laboratory, Iowa State University, Ames, IA 50011.

Abstract

Porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) are major contributors to the porcine respiratory disease complex (PRDC). Routine serological diagnosis and surveillance play an important role in the prevention of PRDC as it is a leading cause of economic losses to the swine industry. We herein describe an advanced microsphere-based immunoassay that permits the simultaneous detection of antibodies to PCV2 and PRRSV; thereby reducing the time and effort involved in testing. Recombinant PRRSV N protein antigen and the PCV2 capsid antigen were coupled to fluorophore dyed beads with distinct spectral addresses. Weekly sera samples from 72 pigs that were experimentally exposed to either PCV2, PRRSV or both PCV2 and PRRSV were used to validate the microbead assay (MBA) in comparison with the gold-standard ELISAs. The kinetics of the PCV2 and PRRSV-specific antibody responses as measured by the microbead assay was comparable to those of the standard assays; Spearman's Rank correlation was 0.72 (p<0.001) for PRRSV and 0.80 (p<0.001) for PCV2. Diagnostic sensitivity and specificity were determined using field sera whose positive or negative status was determined by the standard tests. The diagnostic sensitivity and specificity were both 98% for PCV2 and were 91% and 93% for PRRSV (Kappa coefficient: 0.85 and 0.67 for PCV2 and PRRSV respectively). Multiplexing did not interfere with assay performance or diagnostic sensitivity. Therefore, the described study demonstrates proof of concept for the development of more versatile and economical microbead array based multiplex serological test panels for veterinary use.

Reference:
Lin K, Wang C, Murtaugh M P, Ramamoorthy S. A multiplex method for the simultaneous serological detection of porcine reproductive and respiratory syndrome virus and porcine circovirus type 2. Journal of clinical microbiology 2011 [accepted]

Clustering of and Risk Factors for the Porcine High Fever Disease in a Region of Vietnam

This paper is about risk factors associated with PHFD. It has been suggested that PRRSv might be associated with PHFD, so I included this paper in our blog. In fact, results of this study are in line with what has been reported for PRRSv in terms of risk factors associated with infection and clinical severity of the disease.
Enjoy:

ABSTRACT
Porcine high fever disease (PHFD) emerged in 2006 in China and spread to Vietnam. Little work has been carried out to investigate PHFD risk factors and space–time dynamics. To fill this gap, we investigated probable cases of PHFD at household level as the outcome. A study area, approximately 100 sq. km, was selected from a province of southern Vietnam that had reported the out- break of PHFD in 2008. A survey was conducted in the study area to collect information about swine health problems during 2008. The questionnaire included three sections: general information, clinical signs of disease in pigs and production factors believed to be risk factors. Cases were defined at the household level and included interpretation of clinical signs in series. Logistic regression with a random intercept at the hamlet level was used to assess risk factors for PHFD at the household level. Spatial clustering was investigated using the D-function and a Cuzick–Edward’s test. Spatial clusters were evalu- ated using a spatial relative risk surface and the spatial scan statistic using a Bernoulli model. Space–time clustering was explored using a space–time K-function and Knox’s test. Space–time clusters were evaluated using a space– time permutation model in SaTScan. Of 955 households with questionnaire data, 33.4% were classified as cases. The statistical significance of space and space–time clustering differed between methods employed. The risk factors associated with occurrence of cases were higher numbers of sows and finishing pigs (log 2 transformed), receiving pigs from an external source and the inter- action between using ‘water green crop’ (WGC) as pig feed and owning ducks with or without direct contact with pigs. The interaction between the presence of ducks and feeding WGC to pigs suggested the involvement of pathogens that might be present in water (environment) and could further replicate in or on ducks.

REFERENCE:
Le H, Poljak Z, Deardon R, Dewey C E. Clustering of and Risk Factors for the Porcine High Fever Disease in a Region of Vietnam. Transboundary and emerging diseases 2011; doi:10.1111/j.1865-1682.2011.01239.x.

The assessment of efficacy of porcine reproductive respiratory syndrome virus inactivated vaccine based on the viral quantity and inactivation methods.

Kim H, Kim HK, Jung JH, Choi YJ, Kim J, Um CG, Hyun SB, Shin S, Lee B, Jang G, Kang BK, Moon HJ, Song DS.

Abstract

ABSTRACT:

BACKGROUND:

There have been many efforts to develop efficient vaccines for the control of porcine reproductive and respiratory syndrome virus (PRRSV). Although inactivated PRRSV vaccines are preferred for their safety, they are weak at inducing humoral immune responses and controlling field PRRSV infection, especially when heterologous viruses are involved.

RESULTS:

In all groups, the sample to positive (S/P) ratio of IDEXX ELISA and the virus neutralization (VN) titer remained negative until challenge. While viremia did not reduce in the vaccinated groups, the IDEXX-ELISA-specific immunoglobulin G increased more rapidly and to significantly greater levels 7 days after the challenge in all the vaccinated groups compared to the non-vaccinated groups (p < 0.05). VN titer was significantly different in the 106 PFU/mL PRRSV vaccine-inoculated and binary ethylenimine (BEI)-inactivated groups 22 days after challenge (p < 0.05). Consequently, the inactivated vaccines tested in this study provided weak memory responses with sequential challenge without any obvious active immune responses in the vaccinated pigs.

CONCLUSIONS:

The inactivated vaccine failed to show the humoral immunity, but it showed different immune response after the challenge compared to mock group. Although the 106 PFU/mL-vaccinated and BEI-inactivated groups showed significantly greater VN titers 22 days after challenge, all the groups were already negative for viremia.

Virol J. 2011 Jun 27;8(1):323. [Epub ahead of print]

Porcine reproductive and respiratory syndrome virus (PRRSV) influences infection dynamics of porcine circovirus type 2 (PCV2) subtypes PCV2a and PCV2b by prolonging PCV2 viremia and shedding.

Abstract

The objective of this study was to determine the effect of porcine reproductive and respiratory syndrome virus (PRRSV) infection on porcine circovirus type 2 (PCV2) subtypes a (PCV2a) or b (PCV2b) viremia and shedding characteristics in oral, nasal and fecal samples in experimentally infected pigs. Twenty-three, 2- to 6-week-old pigs were randomly divided into five groups: negative control (n=3), PCV2a-I (n=5), PCV2a-PRRSV-CoI (n=5), PCV2b-I (n=5), and PCV2b-PRRSV-CoI (n=5). Blood, oral, nasal and fecal swabs were collected in regular intervals from day post inoculation (dpi) 0 until dpi 70 and tested by quantitative real-time PCR for the presence and amount of PCV2 DNA and by ELISA for the presence of PCV2-specific antibodies. The results indicate that there were significantly (P<0.05) higher loads of PCV2a and PCV2b DNA in serum, oral swabs, nasal swabs and fecal swabs and a higher prevalence of detectable PCV2 antigen in tissues of pigs concurrently infected with PCV2 and PRRSV compared to pigs singularly infected with PCV2 further confirming that PRRSV enhances replication of PCV2. Moreover, PRRSV infection significantly prolonged the presence of PCV2 DNA in serum and increased the amount of PCV2 DNA in oral and nasal secretions and fecal excretions in the later stages of infection between dpi 28 and 70. Shedding patterns were similar between groups infected with PCV2a and PCV2b, indicating that there was no subtype-specific interaction with the PRRSV isolate used in this study. The results from this study highlight the interaction between PRRSV and PCV2 and the importance of controlling PRRSV infection in order to reduce PCV2 virus loads in pig populations.

Sinha A, Shen H G, Schalk S, Beach N M, Huang Y W, Meng X J, Halbur P G, Opriessnig T. Porcine reproductive and respiratory syndrome virus (PRRSV) influences infection dynamics of porcine circovirus type 2 (PCV2) subtypes PCV2a and PCV2b by prolonging PCV2 viremia and shedding. Veterinary microbiology 2011 [accepted].

nothing new in this past weeks.

Stay tuned. Our system is checking for new "field PRRS" publications in a daily basis. We will keep you posted.
Thank you.

Daniel Linhares

Airborne transmission reviewed and discussed!

Desrosiers R. Transmission of swine pathogens: different means, different needs. Anim Health Res Rev 2011 Jan:1-13.

Abstract

There seems to be two main types of pathogens that cause diseases in swine: those that are mainly introduced through direct pig contacts, and those that are often, and in some situations mainly introduced by indirect transmission means. In this review, the mange mite (Sarcoptes scabiei), toxigenic Pasteurella multocida and Brachyspira hyodysenteriae will be used as examples of the first type, and foot and mouth disease virus, Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome (PRRS) virus as examples of the second. It is now clear from various epidemiological studies as well as experimental and field data that aerosol transmission of some swine pathogens plays an important role in their epidemiology. As previous biosecurity programs did not take this factor into consideration, it can at least partially explain why many of these programs suffered frequent failures and why air filtration is now becoming increasingly popular in North America. Identifying and quantifying transmission means should be a priority for every important infectious disease for which it has not been done.

Keywords: Swine, pathogen, transmission, direct, indirect

Median infectious dose (ID50) of PRRS isolate MN-184 via aerosol exposure

 Cutler T D, Wang C, Hoff S J, Kittawornrat A, Zimmerman J. 2011. Median infectious dose (ID(50)) of porcine reproductive and respiratory syndrome virus isolate MN-184 via aerosol exposure. Veterinary microbiology

Abstract

The median infectious dose (ID(50)) of porcine reproductive and respiratory syndrome (PRRS) virus isolate MN-184 was determined for aerosol exposure. In 7 replicates, 3-week-old pigs (n=58) respired 10l of airborne PRRS virus from a dynamic aerosol toroid (DAT) maintained at -4°C. Thereafter, pigs were housed in isolation and monitored for evidence of infection. Infection occurred at virus concentrations too low to quantify by microinfectivity assays. Therefore, exposure dose was determined using two indirect methods ("calculated" and "theoretical"). "Calculated" virus dose was derived from the concentration of rhodamine B monitored over the exposure sequence. "Theoretical" virus dose was based on the continuous stirred-tank reactor model. The ID(50) estimate was modeled on the proportion of pigs that became infected using the probit and logit link functions for both "calculated" and "theoretical" exposure doses. Based on "calculated" doses, the probit and logit ID(50) estimates were 1×10(-0.13)TCID(50) and 1×10(-0.14)TCID(50), respectively. Based on "theoretical" doses, the probit and logit ID(50) were 1×10(0.26)TCID(50) and 1×10(0.24)TCID(50), respectively. For each point estimate, the 95% confidence interval included the other three point estimates. The results indicated that MN-184 was far more infectious than PRRS virus isolate VR-2332, the only other PRRS virus isolate for which ID(50) has been estimated for airborne exposure. Since aerosol ID(50) estimates are available for only these two isolates, it is uncertain whether one or both of these isolates represent the normal range of PRRS virus infectivity by this route.

Copyright © 2011 Elsevier B.V. All rights reserved.

PMID: 21474258 [PubMed - as supplied by publisher]

Keywords:

PRRS virus, Aerobiology, Transmission, Infectious dose ID50, Dose–response

Comparison of RNA extraction and real-time reverse transcription polymerase chain reaction methods for the detection of Porcine reproductive and respiratory syndrome virus in porcine oral fluid specimens

Chittick W A, Stensland W R, Prickett J R, Strait E L, Harmon K, Yoon K, Wang C, Zimmerman J. 2011. Comparison of RNA extraction and real-time reverse transcription polymerase chain reaction methods for the detection of Porcine reproductive and respiratory syndrome virus in porcine oral fluid specimens. Journal of veterinary diagnostic investigation 23(2):248-253.

Abstract

The objective of the current study was to evaluate various RNA extraction and polymerase chain reaction (PCR) protocols for the detection of Porcine reproductive and respiratory syndrome virus (PRRSV) in porcine oral fluids. Extraction protocols were selected based on ease of use and compatibility with high-throughput, automated systems. The results showed marked differences among extraction protocols, PCR protocols, and combinations thereof in detecting PRRSV in the oral fluid matrix. An important finding was that PCR reactions were partially inhibited by unknown factors in the oral fluid matrix and that inhibition was reduced by use of a higher concentration of PCR enzymes. The results suggest that further optimization of PCR assays for porcine oral fluids is needed and that laboratories should not assume that methods optimized for detection of virus in serum will perform equally with porcine oral fluids.

PMID: 21398443 [PubMed - in process]

Pigs resistant to diseases! Are we ready????

Fan Bin, Onteru S K, Du Z, Garrick D J, Stalder K J, Rothschild M F. 2011. Genome-wide association study identifies Loci for body composition and structural soundness traits in pigs. PLoS ONE 6(2):e14726-e14726.

uouououou! hold on! What does this paper has to do with "Field PRRS" blog?


Well... it is a genome-wide study with pig genome (yes, all - or almost all - pig genes has been mapped and their functions are being studied). This will allow researchers (and genetic companies??) to find out genes associated with specific diseases resistance. Will this research take 1, 2, 3, 10 years to happen? We obviously don't know but let's hope it is soon.

Here is the abstract of this study - enjoy it:

Abstract

BACKGROUND: The recent completion of the swine genome sequencing project and development of a high density porcine SNP array has made genome-wide association (GWA) studies feasible in pigs.

METHODOLOGY/PRINCIPAL FINDINGS: Using Illumina's PorcineSNP60 BeadChip, we performed a pilot GWA study in 820 commercial female pigs phenotyped for backfat, loin muscle area, body conformation in addition to feet and leg (FL) structural soundness traits. A total of 51,385 SNPs were jointly fitted using Bayesian techniques as random effects in a mixture model that assumed a known large proportion (99.5%) of SNPs had zero effect. SNP annotations were implemented through the Sus scrofa Build 9 available from pig Ensembl. We discovered a number of candidate chromosomal regions, and some of them corresponded to QTL regions previously reported. We not only have identified some well-known candidate genes for the traits of interest, such as MC4R (for backfat) and IGF2 (for loin muscle area), but also obtained novel promising genes, including CHCHD3 (for backfat), BMP2 (for loin muscle area, body size and several FL structure traits), and some HOXA family genes (for overall leg action). The candidate regions responsible for body conformation and FL structure soundness did not overlap greatly which implied that these traits were controlled by different genes. Functional clustering analyses classified the genes into categories related to bone and cartilage development, muscle growth and development or the insulin pathway suggesting the traits are regulated by common pathways or gene networks that exert roles at different spatial and temporal stages.

CONCLUSIONS/SIGNIFICANCE: This study is one of the earliest GWA reports on important quantitative traits in pigs, and the findings will contribute to the further biological function analysis of the identified candidate genes and potential utilization of them in marker assisted selection.

Host inhibits replication of European porcine reproductive and respiratory syndrome virus in macrophages by altering differential regulation of type-I interferon transcriptional response

Ait-Ali T, Wilson A D, Carr W, Westcott D G, Frossard J, Mellencamp M A, Mouzaki D, Matika O, Waddington D, Drew T W, Bishop S C, Archibald A L. 2011. Host inhibits replication of European porcine reproductive and respiratory syndrome virus in macrophages by altering differential regulation of type-I interferon transcriptional response. Immunogenetics.

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is an infectious disease caused by a positive RNA strand arterivirus. PRRS virus (PRRSV) interacts primarily with lung macrophages. Little is known how the virus subverts the innate immune response to initiate its replication in alveolar macrophages. Large-scale transcriptional responses of macrophages with different levels of susceptibility to PRRSV infection were compared over 30 h of infection. This study demonstrates a rapid and intense host transcriptional remodelling during the early phase of the replication of the virus which correlates with transient repression of type-I interferon transcript as early as 8 h post-infection. These results support the suggestion from previous studies that host innate immune response inhibits replication of European porcine reproductive and respiratory syndrome virus in macrophages by altering differential regulation of type-I interferon transcriptional response.

Keywords  Swine – Innate immunity – Alveolar macrophage – PRRSV – Interferon response

Porcine reproductive and respiratory syndrome virus in Ontario, Canada 1999-2010: genetic diversity and restriction fragment length polymorphisms

Abstract

Classification of PRRSV field isolates (n = 505) in Ontario from 1999-2010, based on a global type 2 PRRSV phylogenetic framework, revealed genetic diversity comparable to PRRSV in the United States, with isolates in five out of the nine lineages (1, 2, 5, 8, and 9). Importantly, the tree topology indicated a Canadian ancestry for the highly virulent MN184-related strains that first emerged in 2001 in the United States. Mapping the RFLP patterns onto the phylogenetic tree revealed numerous examples of different RFLP patterns located within the same phylogenetic cluster. Statistical analysis showed occurrences where similar RFLP patterns masked diverse genetic distances and instances of close genetic proximity with divergent RFLP patterns. Collectively, extensive genetic diversity prevails in type 2 PRRSV in one region of the North American swine industry, and it is not described adequately by RFLP typing which might have value at the local farm level.

Brar M S, Shi M, Ge Li, Carman S, Murtaugh M P, Leung F C. 2011. Porcine reproductive and respiratory syndrome virus in Ontario, Canada 1999-2010: genetic diversity and restriction fragment length polymorphisms. Journal of general virology [accepted].

An evaluation of ultraviolet light (UV(254)) as a means to inactivate porcine reproductive and respiratory syndrome virus on common farm surfaces and materials

Dee S, Otake S, Deen J. 2011. An evaluation of ultraviolet light (UV(254)) as a means to inactivate porcine reproductive and respiratory syndrome virus on common farm surfaces and materials. Veterinary microbiology (article in press).

Abstract

A study was conducted to assess the effect of UV(254) on the concentration and viability of PRRSV on surfaces and materials commonly encountered on swine farms. A standard quantity (5×10(6)TCID(50), total dose) of a PRRSV modified live vaccine virus was inoculated onto 2 matched sets of surfaces/materials including wood, plastic, latex, rubber, styrofoam, metal, leather, cloth, concrete, cardboard, glass and paper. One set was exposed to UV(254) radiation (treatments) and the other to incandescent light (controls) for a 24h period. During this time, treatments and controls were swabbed at 10min intervals from 0 to 60min post-inoculation (PI) and again at 24h PI. The quantity of PRRSV RNA on each item at each sampling time was calculated by RT-PCR and the presence of viable PRRSV in each sample was determined by swine bioassay. A significant reduction (p<0.0001) in the quantity of PRRSV RNA was demonstrated at 24h PI independent of treatment. In addition, a significant reduction (p=0.012) in the number of UV(254)-treated surfaces which harbored viable virus was observed at 60min (0/12 positive) when compared to control surfaces (5/12 positive). In addition, all UV(254) treated samples collected between 10 and 50min PI were bioassay negative. These results suggest that UV(254) is an effective means to inactivate PRRSV on commonly encountered farm surfaces and materials and inactivation can be accomplished following 10min of exposure.

Keywords: Swine; PRRSV; UV₂₅₄; Surfaces; Inactivation

Discovery of ORF5a

Two papers published in the same issue of the "Journal of General Virology" show the discovery of a new protein "ORF5a", that is supposed to be linked with immune response against PRRS virus. This could lead to development of new tests or new approach to intervention.

Johnson C R, Griggs T F, Gnanandarajah J S, Murtaugh M P. 2011. Novel Structural Protein in Porcine Reproductive and Respiratory Syndrome Virus Encoded in an Alternative Open Reading Frame 5 Present in All Arteriviruses. Journal of general virology 

Firth A E, Zevenhoven-Dobbe J C, Wills N M, Go Y, Balasuriya U, Atkins J F, Snijder E J, Posthuma C. 2011. Discovery of a small arterivirus gene that overlaps the GP5 coding sequence and is important for virus production. Journal of general virology 

Swine health scoring system

Even though this paper is not about PRRSv, it describes a relatively simple method to describe the pig health in numbers. Over some time with this score, practitioners can have an idea of how the "farm health" is doing in numbers beside just mortality...

Alarcon P, Velasova M, Werling D, Stärk K D, Chang Y, Nevel A, Pfeiffer D U, Wieland B. 2011. Assessment and quantification of post-weaning multi-systemic wasting syndrome severity at farm level. Preventive veterinary medicine 98(1):19-28.

Post-weaning multi-systemic wasting syndrome (PMWS) causes major economic losses for the English pig industry and severity of clinical signs and economic impact vary con- siderably between affected farms. We present here a novel approach to quantify severity of PMWS based on morbidity and mortality data and presence of porcine circovirus type 2 (PCV2). In 2008–2009, 147 pig farms across England, non-vaccinating for PCV2, were enrolled in a cross-sectional study. Factor analysis was used to generate variables repre- senting biologically meaningful aspects of variation among qualitative and quantitative morbidity variables. Together with other known variables linked to PMWS, the resulting factors were included in a principal component analysis (PCA) to derive an algorithm for PMWS severity. Factor analysis resulted in two factors: Morbidity Factor 1 (MF1) repre- senting mainly weaner and grower morbidity, and Morbidity Factor 2 (MF2) which mainly reflects variation in finisher morbidity. This indicates that farms either had high morbidity mainly in weaners/growers or mainly in finishers. Subsequent PCA resulted in the extraction of one component representing variation in MF1, post-weaning mortality and percentage of PCV2 PCR positive animals. Component scores were normalised to a value range from 0 to 10 and farms classified into: non or slightly affected farms with a score <4, moderately affected farms with scores 4–6.5 and highly affected farms with a score >6.5. The identified farm level PMWS severities will be used to identify risk factors related to these, to assess the efficacy of PCV2 vaccination and investigating the economic impact of potential control measures.

A modified live PRRSV vaccine and the pathogenic parent strain induce regulatory T cells in pigs naturally infected with Mycoplasma hyopneumoniae. Veterinary immunology and immunopathology

Strong assumptions to start, but interesting hypothesis.

Leroith T, Hammond S, Todd S M, Ni Y, Cecere T, Pelzer K D. 2011. A modified live PRRSV vaccine and the pathogenic parent strain induce regulatory T cells in pigs naturally infected with Mycoplasma hyopneumoniae. Veterinary immunology and immunopathology.

The lack of heterologous protection by porcine reproductive and respiratory syndrome virus (PRRSV) vaccines is currently a major problem in the field. Heterologous protection by PRRS vaccines depends on the ability of the vaccine to induce an interferon gamma (IFN-γ) response. One mechanism by which the virus evades the immune system is by activating regulatory T cells (T(regs)), resulting in induction of interleukin 10 rather than IFN-γ. Our hypothesis that current PRRS vaccines do not differ from pathogenic strains in the ability to induce T(regs) was tested by inoculating three groups of pigs with two pathogenic viruses and an attenuated vaccine strain and evaluating the number of T(regs) in peripheral blood mononuclear cells. Before inoculation, the pigs, although vaccinated became infected naturally with Mycoplasma hyopneumoniae before shipment to our research facility. Our results show that the PRRSV vaccine strain and parent strain are equally able to induce T(regs) in pigs naturally infected with M. hyopneumoniae. Pigs in the vaccine and PRRSV groups had higher lung lesion scores than pigs in the control groups. The results suggest that the exacerbation M. hyopneumoniae respiratory disease may be due to the ability of PRRSV vaccination and viral infection to induce regulatory T cells.

Detection of PRRSV circulation in herds without clinical signs of PRRS: Comparison of five age groups to assess the preferred age group and sample size

Duinhof T F, van Schaik G, van Esch E J B, Wellenberg G J. 2011. Detection of PRRSV circulation in herds without clinical signs of PRRS: Comparison of five age groups to assess the preferred age group and sample size. Veterinary microbiology

A cross-sectional study was conducted to find the most effective diagnostic approach to detect circulation of porcine reproductive and respiratory syndrome virus (PRRSV). The study was performed in 10 Dutch swine herds, with sows and fattening pigs or breeding stock. Herds did not experience clinical signs of PRRS during the last 6 months before sampling, but a PRRSV infection was confirmed at most 2 years before sampling. Blood samples were collected from 5 age groups: sows during early and late gestation, weaners at 9 weeks of age, fatteners or breeding stock at 16 and 22 weeks of age. For each category, 20 serum samples were examined; in total 100 serum samples per herd. Samples were analysed for PRRSV antibodies with ELISA (n = 1002), and rt-PCR when ELISA S/P-ratios were above 1.5 (n = 307) or below 0.4 (n = 187; random selection from each age group). A logistic regression analysis was used to obtain factors associated with the probability of virus detection in a pig (PCR positive test result). Herd, ELISA-result, and age group were included as explanatory variables. Variables remained in the model when statistically significant. ELISA results showed that none of the herds could be considered to be free of PRRSV infection. Mean PRRSV seroprevalence in unvaccinated animals varied between
18% and 82%, and mean PRRS-virus prevalence varied between 0% and 41%. In only one of the 10 herds, no PRRS-virus could be detected. The odds of finding PRRS-virus in blood samples were 8.6 (95% CI, 5.3–13.9) in pigs of 9 weeks of age and 4.6 (95% CI, 3.0–7.0) in pigs of 16 weeks of age, compared with fatteners of 22 weeks of age. This result indicates that 9- to 16-week-old pigs are the preferred age group to detect PRRS-virus, in herds without clinical signs of PRRS. We concluded that PRRS-virus circulation could be detected in 8 out of 9 of the study-herds, with a relatively low number of blood samples. Testing 12 blood samples in both rt-PCR and ELISA, with 6 samples in pigs 9 weeks of age and 6 samples in pigs 16 weeks of age, will lead to a cost-efficient first evaluation of the PRRSV
infection-status in herds without clinical signs of PRRS.

Virology. 2011 Jan 19. [Epub ahead of print]

Chimeric porcine reproductive and respiratory syndrome viruses reveal full function of genotype 1 envelope proteins in the backbone of genotype 2.

Tian D, Zheng H, Zhang R, Zhuang J, Yuan S.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is classified into two genotypes, type 1 and type 2, which share only about 60% genetic identity. Here, we report viable chimeric viruses in which the envelope protein genes from ORF2a to ORF5 of vSHE (type 1) were swapped into the genetic backbone of vAPRRS (type 2). We found that the envelope proteins of genotype 1 were fully functional in genotype 2 PRRSV, and the rescued chimeric progeny viruses showed robust genetic stability and similar replication properties to the parental strains in vitro. To our knowledge, this is the first study to report the substitution of complete ORFs between different genotypes of porcine arterivirus. These findings pave the way to further elucidate the structure-function relationship of PRRSV envelope proteins, and may enable the development of novel marker vaccines that can be used to differentiate vaccinated from infected animals.

Although not a "field" paper, I posted this study because it documents an important step in PRRSv vaccine development knowledge.

Tian D, Zheng H, Zhang R, Zhuang J, Yuan S. 2011. Chimeric porcine reproductive and respiratory syndrome viruses reveal full function of genotype 1 envelope proteins in the backbone of genotype 2. Virology [0042-6822] Tian yr:2011 (electronically available, ahead of print).

Further assessment of air filtration for preventing PRRSV infection in large breeding pig herds

Dee S, Spronk G, Reicks D, Ruen P, Deen J. 2010. Further assessment of air filtration for preventing PRRSV infection in large breeding pig herds. Veterinary record 167(25):976-977.

Short communication that documents the possibility of drastically reducing the likelihood of a breeding herd to become PRRSv infected over a two years period (p=0.0001) by applying negative pressure ventilation system + air filtration + high biosecurity standard procedure.

Terminology for classifying swine herds by porcine reproductive and respiratory syndrome virus status

Holtkamp DJ, Polson DD, Torremorell M, et al. Terminology for classifying swine herds by porcine reproductive and respiratory syndrome virus status. J Swine Health Prod. 2011;19(1):44–56.

Abstract. Standardized terminology for the porcine reproductive and respiratory syndrome virus (PRRSV) status of swine herds is necessary to facilitate communication between veterinarians, swine producers, genetic companies, and other industry participants. It is also required for implementation of regional and national efforts towards PRRSV control and elimination. The purpose of this paper is to provide a herd classification system for describing the PRRSV status of herds, based upon a set of definitions reflecting the biology and ecology of PRRSV. The herd classification system was developed by a definitions committee formed jointly by the American Association of Swine Veterinarians (AASV) and the United States Department of Agriculture PRRS-Coordinated Agricultural Project, and was approved by the AASV Board of Directors on March 9, 2010. The committee included veterinarians from private practice and industry, researchers, and representatives from AASV and the National Pork Board.

Breeding herds, with or without growing pigs on the same premises, are categorized as Positive Unstable (Category I), Positive Stable (Category II), Provisional Negative (Category III), or Negative (Category IV) on the basis of herd shedding and exposure status. Growing-pig herds are categorized as Positive or Negative. Recommended testing procedures and decision rules for herd classification are detailed.