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