A production system’s vulnerability to disease spread can be greatly reduced when selectively identifying a subset of farms as disease control targets.
What was done:
In this study, we used a network approach to describe annual movement patterns between swine farms in three multi-site production systems (1,063 farms) in the United States.
degree: number of farms to which a farm ships or receives pigs
farm’s individual contribution to disease spread via its movements
mean infection potential (MIP), which measures potential incoming and outgoing infection chains
What was found:
Removing farms based on their mean infection potential substantially reduced the potential for transmission of an infectious pathogen through the network when compared to removing farms at random, as shown by a reduction in the magnitude of R0 attributable to contact pattern.
The MIP was more efficient at identifying targets for disease control compared to degree and farm’s contribution to disease spread.
What does this mean?
By targeting disease interventions towards farms based on their mean infection potential, we can substantially reduce the potential for transmission of an infectious pathogen in the contact network, and performed consistently well across production systems.
Fine-scale temporal movement data is important and is necessary for in-depth understanding of the contact structure in developing more efficient disease
Pooling oral fluid samples seems to be a good strategy to determine the status of a farm (positive/negative) for influenza A virus (IAV) and PRRSV.
Sampling water cups using environmental Swiffer™ samples appears to be a sensitive approach to detect IAV at the pen level.
However, sample size has been limited to one farm.
The objective of this project was to compare the sensitivity of pooled pen oral fluids (OF) and environmental samples (Swiffer™ kits on water cups) using individual pen oral fluids as the standard.
Fifteen paired environmental and individual pen OF were collected at days 3, 7, 10, 17, 24 and 31 post placement in two different nursery farms. Environmental samples (ES) were taken using Swiffer™ cloths to sample the bottom of water cups (both pans and bowls), focusing around nipples. After individual samples were collected, pen OF were pooled by 3.
There was an overall sensitivity of 71% (IAV) and 14% (PRRS) for the ES samples compared to individual OF. Pooled oral fluids samples had an overall sensitivity of 50%(IAV)and 80%(PRRSV)relative to individual pen OF.
In summary, ES appears to be a good strategy when sampling for IAV and not a reliable option when trying to diagnose PRRSV.
In the last 9 years, on average 10.2% (Range 3.7% – 22%) of status 4 farms have had a PRRS outbreak during the MSHMP season and in the 2017-2018 season, the cumulative incidence (July to April) is 9.6%.
The lowest PRRS incidence was observed during the 2013/2014 PRRS season; the year that PED entered the US.
PRRS incidence in status 4 farms during the current MSHMP season is not higher than the ones observed in the previous MSHMP seasons.
Reminder: Status 4 sow farms are the farms that considered negative both in shedding and exposure status in the classification document published by the AASV.
Has there been an increase in PRRS outbreaks incidence in status 4 sow farms?
PRRS incidence in status 4 farms from 2009 to April 2018 was compiled and compared with the current MSHMP year using Fisher’s Exact test.
During the current MSHMP year (July 2017- April 2018), 27 status 4 farms have had a PRRS outbreak (6.9% incidence). The average incidence of status 4 farms from 2009 to April 2018 was 9.6%. However, PRRS incidence have varied greatly among years (figure 1). PRRS incidence had its minimum value during the 2013/2014 MSHMP season with a 3.4%. This coincides with the year that porcine epidemic diarrhea virus (PEDv) entered the US.
When comparing the incidence during the 2017/2018 MSHMP year with the incidence observed during the 2015/2016 MSHMP year, a borderline significant difference (p=0.06) was observed.
PRRS incidence in status 4 farms (July 2017 –April 2018) was overall similar to previous years, although slightly higher than July 2016-April 2017, and significantly lower than July 2015-April 2016. Other factors, such as region, may be contributing to the
perception of increased PRRS incidence in status 4 farms.Exploring these factors may help explain the perception of increased
The objectives of the study are to describe the occurrence of PRRSv in the filtered sow herd population within MSHMP and to assess the associations between farm-level factors and the introduction of PRRSv into filtered sow herds. The results of the study may guide practitioners and veterinarians to modify their management and biosecurity practices in filtered sow herds.
Who can enroll?
All filtered sow herds of MSHMP participants will be eligible for the study. The database will be used together with the PRRSv incidence measure to understand occurrence of PRRS before and after filters were installed. A survey has been created to collect farm specific data such as:
Date when herd was filtered
Type of ventilation (negative or positive)
Back draft prevention methodology
Type of pre-filter and filter
Pre-filter and filter replacement frequency
Number of barns and load outs
Frequency of gilt introduction and weaning events
If you are interested in participating, please contact Dr. Cesar Corzo at corzo(at)umn.edu
The majority of veterinarians consider it important to classify sow herd PRRS status.Our survey showed that 8/21 follow AASV guidelines, with the others using alternative criteria.
Half of the surveyed veterinarians use processing fluids as part of their testing protocol for determining sow herd PRRS status.
Most of the respondents mentioned that AASV PRRS classification guidelines should be re-visited.
Twenty-one veterinarians from 12 participant systems and 1 non-participant group completed the questionnaire accounting approximately for 1.5 million sows.
When asked how important it was to classify sow farm PRRS status, 12/21 (57%) answered very important, 8/21 (38%) answered important. Among the most important reasons requiring PRRS status were:
Commingling of pigs downstream,
Timing the Depopulation/Re-population of growing sites with continuous flow, and
Defining gilt acclimation and introduction procedures.
The testing protocol to classify a farm as stable varied across and within systems. However, the most frequent sample collected was due-to-wean blood sampling. Other samples are shown in the figure below.
Strong evidence of area spread was not found after evaluating three farm clusters located in two swine dense regions.
All barns of a nursery/finishing site should be sampled to define status.
Sick pen might not be the best target when sampling for PRRSV in grower pig sites
Background and Objectives
Area spread refers to the transmission of a pathogen (here PRRSV) through small particles in the air as well as through fomites on which the pathogen would have deposited on.
The objective of the study was to determine if the virus detected in a recently infected sow farm was similar to the one detected in neighboring farms (in other words: was local spread a likely source of infection?)
Methods and Results
35 farms were monitored for PRRSV. As soon as a farm broke, all of the neighboring farms were sampled for PRRSV independently of the type of production on site. If a sick pen was present on the farm, effort was made to include it in the sampling. Positive samples were then sequenced to compare to the original virus from the outbreak.
For two of the three area spread assessments performed, no similar sequence to the one obtained from the farm under investigation was found. Also it was not always possible to detect PRRSV in sick pens of the growing pig sites sampled in our study.