Science Page: Use of processing fluids for PRRSV diagnostics

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

Key points

  • Using processing fluids as a diagnostic tool can help us to detect lower PRRS prevalence in the herd.
  • Testicles and tails should be collected in a pail as they are potential spreaders of PRRS in the farrowing room.
  • We should target young parity sows for PRRSV sampling.

Processing fluids PRRS table.gif

What are processing fluids?

In sow farms, piglets get processed during the first week of life. This means that their tails is docked and the males are castrated. The farmer usually collect tails and testicles in a pail to be discarded at a later time.

We propose to use the fluids accumulating at the bottom of the pail to assess the farm PRRSV status.

How did we test those fluids?

The fluids were tested for PRRSV by PCR and the results were compared to the gold standard for this diagnostic: PCR on serum. Sampling was set in a farm that just went through a PRRSV outbreak and 10 litters from various parity sows were selected each week for 8 weeks.

What were the results?

Processing fluids were efficient in detecting PRRSV even if there was only one piglet positive in the litter (determined with the serum samples). Compared to the serum tests, there were 4 false negative samples that were explained by the fact that the virus load in the piglets serums was low and the dilution effect of the processing fluids caused the samples to get negative results. We also found 4 false positive resutls that could be due to cross-contamination of the samples despite the extreme care with which the samples were handled.

Are processing fluids a worthwhile sample?

The agreement between processing fluids and serum results was good and the sensitivity and specificity of the technique was respectively of 83% and 92%. Additionally, this technique requires no further handling of the piglets or use of extra supplies to collect samples and submit them to the laboratory.


Science page: Are patterns of spatiotemporal clustering of PRRSv consistent across years?

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we studied a subset of MSHMP participants located in the Midwest to test if some location/time combinations are more prominent during certain seasons across the years. Data from 358 farms in 10 management systems from 2011 to 2015 was compiled to look for clusters.

The clusters found by the SaTScanTM software are represented below. The red circles represent clusters identified in the time period from January to June, whereas blue ones are July to December. We can note that clusters were identified every year but that they varied with time.

Significant PRRS spatial cluster midwest
Significant spatial clusters for PRRSV in the Midwest between 2011 and 2015.

Key points

  • PRRS cases are recognized to be seasonal and aggregated by geographical space.
  • However, spatiotemporal patterns of PRRS clustering were not consistent across years.
  • Drivers of infection spread may vary over the years.

Future uses for this model can be found in the entire report

Science Page: Incidence risk and incidence rate

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week’s Science page is a follow-up from the one presented last week and focuses on the difference between incidence rate and incidence risk. Those two epidemiological measurements are often mistaken for one another.

Key points from this week edition:

  • Incidence risk is a measure of disease occurrence over a defined period of time. It is a proportion, therefore takes values from 0 to 1 (0% to 100%).
  • Incidence rate takes into account the time an individual is at risk of disease. It is not a proportion since it defines the number of cases per animal or farm time at risk.
  • Incidence risk and Incidence rate are often confused. Incidence risk and rate are numerically the same when the period at risk does not vary across individuals being studied.

Take a look at the complete report to see an example of the difference between incidence risk and incidence rate on farms.


Science Page: PRRS cumulative incidence by status

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

How does PRRS incidence vary based on farm status? This is the question answered in this week’s edition of the Science Page. Three different formulas were used to calculate the incidence in each of the group over type. First, the initial number of farms of each status at the beginning of the year was used as the denominator. Then, the denominator was changed to the total number of farms that entered each status since the beginning of the year. Lastly, weekly incidences calculated for each of the group since the beginning of the year were added. Calculations went back for the last 3 years.

Key points from this week edition:

  • Cumulative incidence is higher in those farms that are under status 2, 2vx and 2fvi.
  • The incidence is lower in farms that had recently an outbreak or those that are completely negative.
  • Different ways of calculating incidence by herd status lead to the same overall conclusion.

Take a look at PRRS incidences in farms of group 2 status, vaccinated or inoculated with live virus over the past years.

PhD seminar: Epidemiological investigation of a non-reportable endemic disease: PRRS in the US

Title: Epidemiological investigation of a non-reportable endemic disease: Porcine reproductive and respiratory syndrome (PRRS) in the US

Presented by:   Pablo Valdes-Donoso

Date:    Friday, June 9, 2017
Time:    3:00 – 4:00 pm
Place:    385-J, AS/VM Building

Abstract: Porcine reproductive and respiratory syndrome (PRRS), caused by a highly mutagenic and resistant RNA-virus, is an endemic disease that has been noted as one of the most important animal production diseases in the US because of its large economic damage on the swine industry. Nonetheless, there is no official control framework for this disease, so producers rely on voluntary regional control programs (RCPs) for its mitigation. Despite efforts to control PRRS, it persists in the environment, affecting a large number of farms every year. Using information shared by a specific RCP (RCP-N212), this dissertation focused on important aspects of PRRS dynamics within an RCP. Specifically, this dissertation encompassed five chapters. An introductory chapter is followed by the second chapter, which quantifies the extent to which RCPs contribute to PRRS control. After that, a prediction of network structure was made to forecast animal movements among farms within the RCP-N212. Then, longitudinal data collected from sow farms were used to measure the impacts of PRRS on production. Finally, a disaggregated disease diffusion model was used to depict PRRS dynamics within the RCP-N212, as well as to evaluate individual and collective strategies adopted by producers. This dissertation provides insight to the evaluation of regional control strategies that may be used as a framework for a formal PRRS control program.

The latest trends in PRRSV diagnostics: less serum samples, more oral fluids, and more 1-7-4 RFLP pattern

Today, Dr. Albert Rovira from the University of Minnesota, Veterinary Diagnostic Laboratory shares with us the trends he has observed in PRRSV diagnostics over the past years. The findings can be found in the slideshow below.

  • The use of tissue samples follows a seasonal pattern and represents clinical cases with a percent of positives of 30%
  • The number of oral fluid samples is increasing. Used for monitoring positive farms and more recently for surveillance in negative farms as well:: 15% of positive samples
  • The number of blood swabs, serum samples, and semen samples, typically used for surveillance in negative farms, is decreasing. Lowest percent of positive samples: 8%
  • RFLP patterns are changing over time. In the past years, 1-7-4 > 1-3-4 or 1-8-4 or 1-4-4
Reminder: what is a RFLP pattern?

RFLP stands for Restriction Fragment Length Polymorphism and is a technique used to detect nucleotide changes in a genetic sequence. The genetic material is put in contact with restriction enzymes which are very specific to a genetic sequence. If the enzyme recognizes the sequence pattern, it will cleave the DNA or RNA fragment. After that, a type is determined based on the number of fragments and its size.

For example with PRRSV, three enzymes are used and the number of fragments each of them produces makes up the numbers of the RFLP pattern. Currently, the RFLP type is not actually performed in the lab. Instead, it is predicted based on the ORF5 RNA sequence and the knowledge of the cutting capabilities of each enzyme.

Therefore, the RFLP pattern gives us a way to cluster PRRSV strains in groups but very little indication about how similar they are to each other.

Science page: Evaluation of positive pressure filtration to reduce aerosol transmission of PRRSV during an experimental challenge of farm access points

This is our Friday rubric: every week a new Science Page from the Swine Health Monitoring Project. The previous editions of the science page are available on our website.

Key points from this week edition:

  • Dilute vaccine aerosolization combined with novel environmental sampling techniques allowed for testing of PRRSV aerosol entry into Positive Pressure Filtration (PPF) farm access points.
  • Under the experimental conditions of this study, positive pressure air speeds >1.85m/s resulted in no aerosol transmission.
  • Ensuring adequate positive pressure air speed through steps taken to increase access point pressure can further reduce the risk of aerosol PRRSV transmission on PPF farms.

The full report on positive pressure filtration and PRRSV transmission via aerosols is available.