Molecular evolution of PRRSV in Europe: Current state of play.

Stadejek T, Stankevicius A, Murtaugh MP, Oleksiewicz MB.

Source

Department of Pathology and Veterinary Diagnostics, Faculty of Veterinary Medicine, Warsaw University of Life Sciences - SGGW, Nowoursynowska 159c, 02-776 Warsaw, Poland. Electronic address: tomasz_stadejek@sggw.pl.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major threat to European swine production. The existence of extensive genetic variation in endemic strains and the presence of highly virulent strains in other geographic regions pose the threat of devastating epidemic outbreaks. Here we describe the current knowledge of genetic variation in European PRRSV isolates, the implications for PRRSV evolution, and the presence of multiple genetic lineages of Type 2 (North American genotype) isolates in Europe. In Type 1 (European genotype) PRRSV, three genetic subtypes are recognized and a fourth subtype appears to be present. Type 2 PRRSV was considered to be genetically homogenous in Europe due to a unique presence of an introduced vaccine strain, but independent introductions of virulent Type 2 field viruses are now evident. In Type 1 PRRSV, only subtype 1 (Lelystad virus-like) circulates in Central and Western Europe and globally. In Eastern Europe, all subtypes are present. The subtypes of Type 1 PRRSV also exhibit length differences in the nucleocapsid protein, ranging in size from 124 to 132 amino acids depending on subtype. This size heterogeneity is unparalleled in the nucleocapsid proteins of Type 2 PRRSV or other viruses. Surprisingly, it affects the C-terminus, otherwise thought to be under strong structural constraints. Finally, divergent subtypes of Type 1 PRRSV have produced high rates of false-negative RT-PCR results in diagnostic tests, and may also degrade the reliability of serodiagnostic assays using the nucleocapsid protein antigen. In summary, the extensive genetic diversity of Type 1 PRRSV is of relevance for understanding nucleocapsid protein structure/function relationships. Further, the extensive genetic diversity of Type 1 PRRSV in Europe, and the presence of diverse Type 2 PRRSV strains, together emphasize the importance of relevant validation of PRRSV diagnostics. More extensive and systematic molecular phylogeny studies are needed to fully understand PRRSV diversity in Europe, to provide swine producers with reliable diagnostics, and to better assess the potential consequences of endemic spread and exotic introductions.

Copyright © 2013 Elsevier B.V. All rights reserved.

PMID:

 

23528651

 

[PubMed - as supplied by publisher]

Stadejek T, Stankevicius A, Murtaugh M P, Oleksiewicz M B. Molecular evolution of PRRSV in Europe: Current state of play. Veterinary microbiology 2013 [in press].

Effect of saliva stabilisers on detection of PRRSv in oral fluid by qPCR

Abstract

This study evaluated the effect of extraction-amplification methods, storage temperature and saliva stabilisers on detection of porcine reproductive and respiratory syndrome virus (PRRSV) RNA by quantitative reverse transcriptase real-time PCR (qRT-PCR) in porcine oral fluid. The diagnostic performance of different extraction-amplification methods was examined using a dilution series of oral fluid spiked with PRRSV. To determine RNA stability, porcine oral fluid, with or without commercially available saliva stabilisers, was spiked with PRRSV, stored at 4°C or room temperature and tested for the presence of PRRSV RNA by qRT-PCR. PRRSV RNA could be detected in oral fluid using all extraction-amplification combinations, but the limit of detection varied amongst different combinations. Storage temperature and saliva stabilisers had an effect on the stability of PRRSV RNA, which could only be detected for 7days when PRRSV spiked oral fluid was kept at 4°C or stabilised at room temperature with a commercial mRNA stabiliser.

Copyright © 2013 Elsevier Ltd. All rights reserved.

Decorte I, Van der Stede Y, Nauwynck H, De Regge N, Cay A B. Effect of saliva stabilisers on detection of porcine reproductive and respiratory syndrome virus in oral fluid by quantitative reverse transcriptase real-time PCR. The veterinary journal 2013 [in press].

In vitro inactivation of PRRSv and PRv by acidic electrolyzed water

Abstract

Slightly acidic electrolyzed water (SAEW, pH 5.0-6.5) is a novel disinfectant with environmentally friendly broad spectrum microbial decontamination properties which could have significant utility on farm. Two of the most important pathogenic viruses in pigs are porcine reproductive and respiratory syndrome virus (PRRSV) and pseudorabies virus (PRV). The aim of this study was to evaluate the viricidal effectiveness of SAEW against PRRSV and PRV in vitro under different available chlorine concentrations (ACCs, 30, 50 and 70mg/L), treatment times (5, 10 and 15min) and temperatures (4, 20, 40 and 60°C), respectively. SAEW had a strong viricidal activity against both PRRSV and PRV. This activity increased with increasing ACC, treatment time and temperature. PRRSV and PRV titres of 7.0log₁₀TCID₅₀/mL and 5.9log₁₀TCID₅₀/mL, respectively, were completely inactivated by SAEW at an ACC of ⩾50mg/L for 10min even though SAEW had no negative effect on the host cells. SAEW thus shows promise as a disinfectant for use on pig farms to reduce the spread of both PRRSV and PRV, and to limit the morbidity associated with those viruses.

Copyright © 2013 Elsevier Ltd. All rights reserved.

Hao X, Shen Z, Wang J, Zhang Q, Li B, Wang C, Cao W. In vitro inactivation of porcine reproductive and respiratory syndrome virus and pseudorabies virus by slightly acidic electrolyzed water. The veterinary journal 2013 [in press].

Effects on boar semen quality after infection with PRRSv: a case report

Abstract

ABSTRACT: The effect of porcine reproductive and respiratory syndrome virus (PRRSV) on semen quality was examined in a group of 11 spontaneously infected boars in a commercial boar stud. Semen samples were collected 4 weeks prior to 4 weeks post-infection (wpi). Infection with PRRSV of the European genotype subtype 1 (EU-1) was verified by specific quantitative real-time polymerase chain reaction (RT-PCR) in 36% of the serum samples. All boars seroconverted before 4 wpi and remained in normal condition throughout the study. Comparison of the percentage of morphologically intact spermatozoa revealed an increase of acrosome-defective spermatozoa (P = 0.012) between -4 and 4 wpi. Significant deleterious effects on semen quality were detected for membrane integrity when semen had been stored for 2 days after sampling. Analysis of sperm subpopulations in a thermoresistance test on day 7 after sampling revealed alterations in the percentage of circular, progressively motile spermatozoa (P = 0.013), in the percentage of non-linear, progressively motile spermatozoa (P = 0.01), and on the amplitude of lateral sperm head displacement (P = 0.047). There was no difference in the incidence of mitochondrially active spermatozoa (P = 0.075). Investigation of routine production data between pre- and post-infection status showed no differences on ejaculate volume (P = 0.417), sperm concentration (P = 0.788), and percentage of motile spermatozoa (P = 0.321). This case report provides insights into a potential control strategy for PRRSV outbreaks in boar studs.

PMID:

 

23442207

 

[PubMed - as supplied by publisher]

Schulze M, Revilla-FernÃndez S, Schmoll F, Grossfeld R, Griessler A. Effects on boar semen quality after infection with porcine reproductive and respiratory syndrome virus: a case report. Acta Veterinaria Scandinavica 2013;55(1):16-16.

Bayesian analysis of risk factors for infection with PRRSv in Ontario using monitoring data

Abstract

Porcine reproductive and respiratory syndrome (PRRS) has a worldwide distribution. This economically important endemic disease causes reproductive failure in breeding stock and respiratory tract illness in young pigs. In Ontario restricted fragment length polymorphism (RFLP) 1-18-4 has been determined as one of the most common virus genotypes. Individual-level models (ILMs) for infectious diseases, fitted in a Bayesian MCMC framework, have been used to describe both the spatial and temporal spread of diseases. They are an intuitive and flexible class of models that can take into account population heterogeneity via various individual-level covariates. The objective of this study is to identify relative importance of risk factors for the spread of the genotype 1-18-4 from monitoring data in southern Ontario using ILMs. Specifically, we explore networks through which resources are obtained or delivered, as well as the ownership structure of herds, and identify factors that may be contributing to high risk of infection. A population of 316 herds which experienced their PRRS outbreaks between September 2004 and August 2007 are included in the analyses, in which 194 (61%) are sow herds. During the study period, 45 herds (27 sow herds) experienced their first outbreak due to RFLP 1-18-4. Our results show that the three relatively most important factors for the spread of 1-18-4 genotype in Ontario swine herds were sharing the same herd ownership, gilt source and market trucks. All other networks had relatively smaller impact on spread of this PRRSV genotype. Spatial proximity could not be identified as important contributor to spread. Our findings also suggest that gilt acclimation should be practiced whenever possible and appropriate to reduce the risk for the herd and for others as it is already widely implemented and recommended in the North American swine industry.

Copyright © 2013 Elsevier B.V. All rights reserved.

PMID:

 

23416041

 

[PubMed - as supplied by publisher]

Kwong G P, Poljak Z, Deardon R, Dewey C E. Bayesian analysis of risk factors for infection with a genotype of porcine reproductive and respiratory syndrome virus in Ontario swine herds using monitoring data. Preventive veterinary medicine 2013 [in press].

Control of PRRS through genetic improvements in disease resistance and tolerance

Abstract

Infections caused by porcine reproductive and respiratory syndrome virus (PRRSV) have a severe economic impact on pig production in North America, Europe, and Asia. The emergence and eventual predominance of PRRS in the 1990s are the likely result of changes in the pork industry initiated in the late 1970s, which allowed the virus to occupy a unique niche within a modern commercial production system. PRRSV infection is responsible for severe clinical disease, but can maintain a life-long subclinical infection, as well as participate in several polymicrobial syndromes. Current vaccines lessen clinical signs, but are of limited use for disease control and elimination. The relatively poor protective immunity following vaccination is a function of the virus's capacity to generate a large degree of genetic diversity, combined with several strategies to evade innate and adaptive immune responses. In 2007, the PRRS Host Genetics consortium (PHGC) was established to explore the role of host genetics as an avenue for PRRS control. The PHGC model for PRRS incorporates the experimental infection of large numbers of growing pigs and has created the opportunity to study experimental PRRSV infection at the population level. The results show that pigs can be placed into distinct phenotypic groups, including pigs that show resistance (i.e., low virus load) or pigs that exhibit "tolerance" to infection. Tolerance was illustrated by pigs that gain weight normally in the face of a relatively high virus load. Genome-wide association analysis has identified a region on chromosome 4 (SSC4) correlated with resistance; i.e., lower cumulative virus load within the first 42 days of infection. The genomic region is near a family of genes involved in innate immunity. The region is also associated with higher weight gain in challenged pigs, suggesting that pigs with the resistance alleles don't seem to simultaneously experience reduction in growth, i.e., that resistance and tolerance are not antagonistically related. These results create the opportunity to develop breeding programs that will produce pigs with increased resistance to PRRS and simultaneously high growth rate. The identification of genomic markers involved in actual tolerance will likely prove more difficult, primarily because tolerance is difficult to quantify and because tolerance mechanism are still poorly understood. Another avenue of study includes the identification of genomic markers related to improved response following vaccination.

KEYWORDS:

PRRS resistance, genome-wide association study, porcine reproductive and respiratory syndrome

PMID:

 

23403935

 

[PubMed]

Rowland R R, Lunney J, Dekkers J. Control of porcine reproductive and respiratory syndrome (PRRS) through genetic improvements in disease resistance and tolerance. Frontiers in genetics 2012;3:260-260.

Risk Assessment of the Introduction of PRRSv via Boar Semen into Switzerland as an Example of a PRRSV-Free Country

Risk Assessment of the Introduction of Porcine Reproductive and Respiratory Syndrome Virus via Boar Semen into Switzerland as an Example of a PRRSV-Free Country.

Nathues C, Zimmerli U, Hauser R, Nathues H, Grosse Beilage E, Schüpbach-Regula G.

Source

Veterinary Public Health Institute, University of Berne, Liebefeld, Switzerland.

Abstract

Switzerland is currently porcine reproductive and respiratory syndrome virus (PRRSV) free, but semen imports from PRRSV-infected European countries are increasing. As the virus can be transmitted via semen, for example, when a free boar stud becomes infected, and the risk of its import in terms of PRRSV introduction is unknown, the annual probability to accidentally import the virus into Switzerland was estimated in a risk assessment. A quantitative stochastic model was set up with data comprised by import figures of 2010, interviews with boar stud owners and expert opinion. It resulted in an annual median number of 0.18 imported ejaculates (= imported semen doses from one collection from one donor) from PRRSV-infected boars. Hence, one infected ejaculate would be imported every 6 years and infect a mean of 10 sows. These results suggest that under current circumstances, there is a substantial risk of PRRSV introduction into Switzerland via imported boar semen and that measures to enhance safety of imports should be taken. The time from infection of a previously negative boar stud to its detection had the highest impact on the number of imported 'positive' ejaculates. Therefore, emphasis should be placed on PRRSV monitoring protocols in boar studs. Results indicated that a substantial increase in safety could only be achieved with much tighter sampling protocols than currently performed. Generally, the model could easily be customized for other applications like other countries or regions or even sow farms that want to estimate their risk when purchasing semen from a particular boar stud.

© 2013 Blackwell Verlag GmbH.

PMID:

 

23356485

 

[PubMed - as supplied by publisher]

Nathues C, Zimmerli U, Hauser R, Nathues H, Grosse Beilage E, Schupbach Regula G. Risk Assessment of the Introduction of Porcine Reproductive and Respiratory Syndrome Virus via Boar Semen into Switzerland as an Example of a PRRSV-Free Country. Transboundary and emerging diseases 2013 [in press]