Tuesday, April 18, 2017

Geographical factors for PRRS outbreaks

 2017 Apr 17;12(4):e0172638. doi: 10.1371/journal.pone.0172638. eCollection 2017.

Land altitude, slope, and coverage as risk factors for Porcine Reproductive and Respiratory Syndrome (PRRS) outbreaks in the United States.


Abstract

Porcine reproductive and respiratory syndrome (PRRS) is, arguably, the most impactful disease on the North American swine industry. The Swine Health Monitoring Project (SHMP) is a national volunteer initiative aimed at monitoring incidence and, ultimately, supporting swine disease control, including PRRS. Data collected through the SHMP currently represents approximately 42% of the sow population of the United States. The objective of the study here was to investigate the association between geographical factors (including land elevation, and land coverage) and PRRS incidence as recorded in the SHMP. Weekly PRRS status data from sites participating in the SHMP from 2009 to 2016 (n = 706) was assessed. Number of PRRS outbreaks, years of participation in the SHMP, and site location were collected from the SHMP database. Environmental features hypothesized to influence PRRS risk included land coverage (cultivated areas, shrubs and trees), land altitude (in meters above sea level) and land slope (in degrees compared to surrounding areas). Other risk factors considered included region, production system to which the site belonged, herd size, and swine density in the area in which the site was located. Land-related variables and pig density were captured in raster format from a number of sources and extracted to points (farm locations). A mixed-effects Poisson regression model was built; and dependence among sites that belonged to a given production system was accounted for using a random effect at the system level. The annual mean and median number of outbreaks per farm was 1.38 (SD: 1.6), and 1 (IQR: 2.0), respectively. The maximum annual number of outbreaks per farm was 9, and approximately 40% of the farms did not report any outbreak. Results from the final multivariable model suggested that increments of swine density and herd size increased the risk for PRRS outbreaks (P < 0.01). Even though altitude (meters above sea level) was not significant in the final model, farms located in terrains with a slope of 9% or higher had lower rates of PRRS outbreaks compared to farms located in terrains with slopes lower than 2% (P < 0.01). Finally, being located in an area of shrubs/ herbaceous cover and trees lowered the incidence rate of PRRS outbreaks compared to being located in cultivated/ managed areas (P < 0.05). In conclusion, highly inclined terrains were associated with fewer PRRS outbreaks in US sow farms, as was the presence of shrubs and trees when compared to cultivated/ managed areas. Influence of terrain characteristics on spread of airborne diseases, such as PRRS, may help to predicting disease risk, and effective planning of measures intended to mitigate and prevent risk of infection.
PMID:
 
28414720
 
DOI:
 
10.1371/journal.pone.0172638

Wednesday, April 5, 2017

Unraveling the contact patterns and network structure of pig shipments in the US and its association with PRRSV outbreaks.

 2017 Mar 1;138:113-123. doi: 10.1016/j.prevetmed.2017.02.001. Epub 2017 Feb 2.

Unraveling the contact patterns and network structure of pig shipments in the United States and its association with porcine reproductive and respiratory syndrome virus (PRRSVoutbreaks.

Author information

1
Center for Animal Disease Modeling and Surveillance (CADMS), Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA. Electronic address: pvmlee@ucdavis.edu.
2
Boehringer - Ingelheim Vetmedica, Inc., St. Joseph, MO, USA.
3
Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA.
4
Center for Animal Disease Modeling and Surveillance (CADMS), Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA.

Abstract

The analysis of the pork value chain is becoming key to understanding the risk of infectious disease dissemination in the swine industry. In this study, we used social network analysis to characterize the swine shipment network structure and properties in a typical multisite swine production system in the US. We also aimed to evaluate the association between network properties and porcine respiratory and reproductive syndrome virus (PRRSV) transmission between production sites. We analyzed the 109,868 swine shipments transporting over 93 million swine between more than 500 production sites from 2012 to 2014. A total of 248 PRRSV positive occurrences were reported from 79 production sites during those 3 years. The temporal dynamics of swine shipments was evaluated by computing network properties in one-month and three-month networks. The association of PRRS occurrence in sow farms with centrality properties from one-month and three-month networks was assessed by using the multilevel logistic regression. All monthly networks showed a scale-free network topology with positive degree assortativity. The regression model revealed that out-degree centrality had a negative association with PRRS occurrence in sow farms in both one-month and three-month networks [OR=0.79 (95% CI, 0.63-0.99) in one-month network and 0.56 (95% CI, 0.36, 0.88) in three-month network] and in-closeness centrality model was positively associated with PRRS occurrence in sow farms in the three-month network [OR=2.45 (95% CI, 1.14-5.26)]. We also describe how the occurrence of porcine epidemic diarrheac (PED) outbreaks severely affected the network structure as well as the PRRS occurrence reports and its association with centrality measures in sow farms. The structure of the swine shipment network and the connectivity between production sites influenced on the PRRSV transmission. The use of network topology and characteristics combining with spatial analysis based on fine scale geographical location of production sites will be useful to inform the design of more cost-efficient, risk-based surveillance and control measures for PRRSV as well as other diseases in the US swine industry.

KEYWORDS: 

Infectious disease; PED; PRRS; Pork value chain; Social network analysis; Swine
PMID:
 
28237226
 
DOI:
 
10.1016/j.prevetmed.2017.02.001

Monday, April 3, 2017

Quasispecies evolution of PRRSv early during in vivo infection

 2017 Mar 30. doi: 10.1007/s00705-017-3342-0. [Epub ahead of print]

Quasispecies evolution of the prototypical genotype 1 porcine reproductive and respiratory syndrome virus early during in vivo infection is rapid and tissue specific.

Author information

1
PAPRSB Institute of Health Sciences, Universiti Brunei Darussalam, Bandar Seri Begawan, Brunei.
2
The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, UK.
3
Northwest A&F University, Xianyang, China.
4
Animal and Plant Health Agency, Preston, UK.
5
The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, UK. tahar.aitali@roslin.ed.ac.uk.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major infectious threat to the pig industry worldwide. Increasing evidence suggests that microevolution within a quasispecies population can give rise to high sequence heterogeneity in PRRSV; potentially impacting the pathogenicity of the virus. Here, we report on micro-evolutionary events taking place within the viral quasispecies population in lung and lymph node 3 days post infection (dpi) following experimental in vivo infection with the prototypical Lelystad PRRSV (LV). Sequence analysis revealed 16 high frequency single nucleotide variants (SNV) or differences from the reference LV genome which are assumed to be representative of the consensus inoculum genome. Additionally, 49 other low frequency SNVs were also found in the inoculum population. At 3 dpi, a total of 9 and 10 SNVs of varying frequencies could already be detected in the LV population infecting the lung and lymph nodes, respectively. Interestingly, of these, three and four novel SNVs emerged independently in the two respective tissues when compared to the inoculum. The remaining variants, though already present at lower frequencies in the inoculum, were positively selected and their frequency increased within the quasispecies population. Hence, we were able to determine directly from tissues infected with PRRSV the repertoire of genetic variants within the viral quasispecies population. Our data also suggest that microevolution of these variants is rapid and some may be tissue-specific.
PMID:
 
28361286
 
DOI:
 
10.1007/s00705-017-3342-0

Tuesday, March 14, 2017

(!) Sampling guidelines for oral fluids-based surveys of group-housed animals

 2017 Feb 17. pii: S0378-1135(16)30527-2. doi: 10.1016/j.vetmic.2017.02.004. [Epub ahead of print]

Sampling guidelines for oral fluid-based surveys of group-housed animals.

Author information

1
Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA. Electronic address: mrotolo@iastate.edu.
2
Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA, USA.
3
Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA; Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA, USA.
4
Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA.
5
Smithfield Foods, Algona, IA, USA.

Abstract

Formulas and software for calculating sample size for surveys based on individual animal samples are readily available. However, sample size formulas are not available for oral fluids and other aggregate samples that are increasingly used in production settings. Therefore, the objective of this study was to develop sampling guidelines for oral fluid-based porcine reproductive and respiratory syndrome virus (PRRSV) surveys in commercial swine farms. Oral fluid samples were collected in 9 weekly samplings from all pens in 3 barns on one production site beginning shortly after placement of weaned pigs. Samples (n=972) were tested by real-time reverse-transcription PCR (RT-rtPCR) and the binary results analyzed using a piecewise exponential survival model for interval-censored, time-to-event data with misclassification. Thereafter, simulation studies were used to study the barn-level probability of PRRSV detection as a function of sample size, sample allocation (simple random sampling vs fixed spatial sampling), assay diagnostic sensitivity and specificity, and pen-level prevalence. These studies provided estimates of the probability of detection by sample size and within-barn prevalence. Detection using fixed spatial sampling was as good as, or better than, simple random sampling. Sampling multiple barns on a site increased the probability of detection with the number of barns sampled. These results are relevant to PRRSV control or elimination projects at the herd, regional, or national levels, but the results are also broadly applicable to contagious pathogens of swine for which oral fluid tests of equivalent performance are available.

KEYWORDS: 

Modeling; Monitoring; Oral fluid; PRRSV; Probability of detection; Sample size; Sampling; Surveillance
PMID:
 
28284415
 
DOI:
 
10.1016/j.vetmic.2017.02.004

Transmission of PRRSv from and from vaccinated pigs

 2017 Mar;201:18-25. doi: 10.1016/j.vetmic.2016.12.012. Epub 2016 Dec 23.

Transmission of Porcine reproductive and respiratory syndrome virus 1 to and from vaccinated pigs in a one-to-one model.

Author information

1
UAB, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain; Departament de Sanitat i Anatomia Animals, Facultat de Veterinària, UAB, 08193 Bellaterra, Barcelona, Spain.
2
Departament de Sanitat i Anatomia Animals, Facultat de Veterinària, UAB, 08193 Bellaterra, Barcelona, Spain.
3
UAB, Centre de Recerca en Sanitat Animal (CReSA, IRTA-UAB), Campus de la Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain; Departament de Sanitat i Anatomia Animals, Facultat de Veterinària, UAB, 08193 Bellaterra, Barcelona, Spain. Electronic address: enric.mateu@uab.cat.

Abstract

The present study examined transmission by contact of Porcine reproductive and respiratory syndrome virus (PRRSV) 1 in a one-to-one model to vaccinated and unvaccinated pigs and from vaccinated infected pigs to other vaccinated pigs. The experiment started by randomly assigning weaned pigs to groups V (n=24) and U (n=26). V pigs were vaccinated with a commercial live attenuated PRRSV vaccine and the U animals were kept as unvaccinated controls. Twenty-eight days later, 6U pigs were separated and allocated in individual boxes. The remaining 20U pigs were intranasally inoculated with PRRSV isolate 3267 (from now on designated as seeder (S) pigs) and 48h later were distributed in boxes where they were commingled with either V or U pigs in 1:1 groups (first contact phase), resulting in 6S:U and 14S:V pairs. As soon as a V pig was detected to be viremic because of contact with a S, the infected V (from now on designated as Vinf) was transferred (<24h after detection) to a new pen where it was comingled with a new V pig (designated as V2) in a second contact phase. For the first contact phase, pigs were maintained 21days at maximum and for the second contact phase the maximum exposure period was 14days. Two V pigs tested positive for the vaccine virus (>99.5% similarity) when they were relocated with the corresponding V2 pigs and they were removed; thus, only 12Vinf were finally considered. All V pigs (12/12) exposed to S animals became infected although the first detection of viremia occurred at 13.6±3.6days, one week later than in U (p<0.05). Also, duration of viremia was shorter for Vinf compared to U, (5.5±4.3days versus 12.5±2.7days). The Vinf group showed remarkable individual variability: eight animals had a viremic period of 5 or less days (3.0±1.4) while the remaining four had a longer viremic period of more than one week (10.8±2.9). This situation was not observed in U. In the second contact phase, transmission from Vinf to V2 pigs occurred in 7/8 cases (87.5%). The mean duration of viremia for V2 was 4.8±3.4 and two different patterns were again observed: two animals had viremias of 9-10days and the rest averaged 3.0±1.4days (range: 2-5days). Vaccinated groups Vinf and V2 had a significantly lower PRRSV shedding in oral fluids for at least the first 9days after the onset of the viremia compared to U, and shedding for V2 was even significantly lower (p<0.05) than shedding for Vinf. Our experimental design reproduced the worst-case scenario for evaluating the effect of vaccination and, under such conditions; it was still efficacious in slowering PRRSV transmission and decreasing the global viral load and particularly oral shedding.

KEYWORDS: 

Porcine reproductive and respiratory syndrome virus; Transmission; Vaccination
PMID:
 
28284607
 
DOI:
 
10.1016/j.vetmic.2016.12.012

Monday, March 13, 2017

Outbreak investigations of PRRSV in regional control projects in Ontario, Canada

 2017 Feb;64(1):89-100. doi: 10.1111/tbed.12343. Epub 2015 Mar 11.

Investigation of the Occurrence of Porcine Reproductive and Respiratory Virus in Swine HerdsParticipating in an Area Regional Control and Elimination Project in OntarioCanada.

Author information

1
Department of Population Medicine, University of Guelph, Guelph, ON, Canada.
2
Ontario Swine Health Advisory Board, Stratford, ON, Canada.
3
Strategic Solutions Group, Puslinch, ON, Canada.
4
Animal Health Laboratory, University of Guelph, Guelph, ON, Canada.

Abstract

The main goal of this study was to investigate the occurrence of porcine reproductive and respiratory syndrome virus (PRRSV)-specific genotypes in swine sites in Ontario (Canada) using molecular, spatial and network data from a porcine reproductive and respiratorysyndrome (PRRS) regional control project. For each site, location, animal movement service provider (truck companies), PRRSV status and sequencing data of the open reading frame 5 (ORF5) were obtained. Three-kilometre buffers were created to evaluate neighbourhood characteristics for each site. Social network analysis was conducted on swine sites and trucking companies to assemble the network and define network components. Three different PRRSV genotypes were used as outcomes for statistical analysis based on the region's phylogenetic tree of the ORF5. Multivariable exact logistic regression was conducted to investigate the association between being positive for a specific genotype and two main exposures of interest: (i) having at least one neighbour within three km also positive for the same genotype outside the production system and (ii) having at least one positive site for the same genotype in the same truck network component outside the production system. Results showed that the importance of area spread and truck network on PRRSV occurrence differed according to genotype. Additionally, the Ontario PRRS database appears suitable for conducting regional disease investigations. Finally, the use of relatively new tools available for network, spatial and molecular analysis could be useful in investigationcontrol and prevention of endemic infectious diseases in animal populations.

KEYWORDS: 

Porcine reproductive and respiratory syndrome; disease investigation; molecular epidemiology; network analysis
PMID:
 
25766306
 
DOI:
 
10.1111/tbed.12343

MLV vaccines to reduce seminal shedding of type 1 PRRSv

 2017 Feb;64(1):194-203. doi: 10.1111/tbed.12361. Epub 2015 Apr 16.

Two Commercial Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)-ModifiedLive Vaccines Reduce Seminal Shedding of Type 1 PRRSV but not Type 2 PRRSV in InfectedBoars.

Author information

1
Department of Veterinary Pathology, College of Veterinary Medicine, Seoul National University, Seoul, Korea.

Abstract

The objective of this study was to compare the effects of two commercial type 1 porcine reproductive and respiratory syndrome virus(PRRSV)-modified live vaccines on type 1 and type 2 PRRSV shedding in the semen of experimentally infected boars. Upon challenge with PRRSV, unvaccinated boars exhibited an increase in daily rectal temperature (39.4-39.7°C). Vaccination of boars with type 1PRRSV significantly reduced the amount of type 1 PRRSV load in blood and semen after challenge with type 1 PRRSV, but barely reduced the amount of type 2 PRRSV load in blood and semen after the type 2 PRRSV challenge. There were no significant differences in the reduction of viremia and seminal shedding of type 1 and type 2 PRRSV between the two commercial vaccines. The seminalshedding of PRRSV is independent of viremia. The reduction of type 1 PRRSV seminal shedding coincided with the appearance of type1 PRRSV-specific interferon-γ secreting cells (IFN-γ-SC) in vaccinated type 1 PRRSV-challenged boars. The frequencies of type 1PRRSV-specific IFN-γ-SC induced by type 1 PRRSV vaccine are relatively high compared to type 2 PRRSV-specific IFN-γ-SC induced by the same vaccine which may explain why type 1 PRRSV vaccine is more effective in reducing seminal shedding of type 1 PRRSVwhen compared to type 2 PRRSV in vaccinated challenged boars. These results provide clinical information on how to reduce seminalshedding of type 1 PRRSV in boars using type 1 PRRSV-modified live vaccine.

KEYWORDS: 

boar; cross-protection; porcine reproductive and respiratory syndrome virus; semen; vaccine
PMID:
 
25879825
 
DOI:
 
10.1111/tbed.12361