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.