PEDv Update – December 4, 2013

December 4, 2013 — 

1. Research updates
   1. Environmental Stability of PEDv courtesy of S Goyal, University of MN
      Previous findings
      • Virus causes clinical signs & SI infection even at 10^-8 dilution (PCR negative)
      • Infectious virus survives for >28 days in fecal slurry at -20⁰C
      • Infectious virus survives for >28 days in wet feed mixture at room temperature
      • Infectious virus survives for less than 2 weeks in dry feed mixture at room temperature
      
      New Results
      • Further evaluation of PEDv survival in fecal slurry was performed at room temperature and 4⁰C under three different relative humidity (RH) levels: 30%, 50%, and 70%.
      • The virus survived in room temperature fecal slurry for at least 14 days but less than 28 days. These results indicate that there is no effect of relative humidity on virus survival.
      • The virus survived in 4⁰C fecal slurry for at least 28 days at all three relative humidity levels.
   2. PEDv in Flies Bioassay Results
      Goyal reported the first PED PCR positive sample collected from flies on 11/11/2013 with a Ct value of 30.44 (after 10 ml of media was used to saturate the 30 collected flies). This sample was used in a bioassay to determine if the virus is alive. The virus was not alive as it did not cause clinical signs (diarrhea/vomiting) and could not be detected via PCR in the small intestines 2 days post-inoculation.
   3. PEDv Lateral Spread Study Update – UMN Swine Health Monitoring Project
      • North Carolina Cluster Preliminary Report
        155 PEDv positive sites in North Carolina are participating as case farms in a large cluster analysis to identify risk factors for lateral spread of PEDv. These case farms are each matched to 2 negative control sites and administered a biosecurity questionnaire for comparison of potential risk factors between cases and controls. All 2,072 sites in the area are also being monitored for PEDv status. The geographic coordinates and date of infection in weekly updates are being used to identify spatial patterns of epidemic spread.
        Data from the first 17 / 47 questionnaires including 8 positive and 9 negative sites were summarized.* These findings are preliminary and presented for informational purpose. These results WILL change as more data are available and analyzed.
        • Positive sites had average herd size of 4,683 vs. 4,035 for negative sites.
        • Positive sites were in more dense regions than negative sites.
        • There was approximately double the frequency of feed truck deliveries to positive sites compared to negative sites.
        • There were approximately double the frequency of trucks visiting to remove pigs of any age from positive sites compared to negative sites
        • 40% more farms in the positive group had culls removed from the site in the two weeks preceding infection.
        *Note: the negative sites in this preliminary analysis are NOT the identified controls for the specific positive sites, simply the control sites that we have questionnaires completed for at this time.
        
        

        Update of all 2,072 sites in the region as of 11/15/2013:

        • There are 420 positive sites in the region
        • There is an average incidence of 49 newly infected sites per week being reported over the last 3 weeks (from lateral spread and movement of pigs).
        
        Spatial analysis as reported previously
        • Cases immediately following previous infections occurred directionally at 20 degrees NE on average
        • Odds of being infected given distance to nearest known positive neighboring site:
          • within 1 mile = 8.4x
          • within 2 miles = 6.3x
          • Within 3 miles = no increase
        • Sites with sows and grow/finish pigs had highest incidence of PEDv
        • Site capacity was not significantly associated with PEDv
      • Oklahoma Cluster Preliminary Report
        Spatial analysis
        • Proximity to positive sites increased the risk of becoming PEDv positive
        • A 5 day delay between the first case and subsequent cases indicated infection from the earliest case by a mechanism that may depend on geographic proximity
        • Week 3 of the epidemic showed a case appearing far from other cases which may indicate transmission via truck movement.
        
        Source: UMN Swine Health Monitoring Project, November 22, 2013
2. Weekly new case report – The weekly new case report from NAHLN is posted on the AASV PEDv webpage. There were no new states reporting biological cases this week. 96 new cases were reported for the week of 11/24/2013 bringing the total number of cases reported to 1373.