PRRSV and PCV2

Posted by Dr. Steve Dudley on June 29 2009 13:49

• These two diseases have been the most economically important diseases recently.
• Prevention and control strategies have been an area of focus in herd health.
• We have come a long way in our understanding of these pathogens, but there is still much to learn and accomplish. 

• Porcine Reproductive and Respiratory Syndrome Virus
• PRRS is the disease..... PRRSV is the virus
• Several Other Names
  • SAMS
  • SMD
  • SIRS
  • Blue Ear
  • Lelystad
• Most economically important disease of swine
  • $650 Million Annually
  • Has dictated large amount of production System design.

PRRSV: The Basics

• Family of viruses known as Arteriviruses
• Much heterogeneity in the genome
  • RNA viruses have errors in transcription
  • Strains vary markedly in virulence
• European and U.S. strains genetically distinct, although thy arose around the same time.
• No Protective epitopes have really been identified
• Replicates within the white blood cells in the lungs (PAMS)

PRRSV Testing

• Polymerase Chain Reaction (PCR)
  • Detects virus. Very sensitive. Beware of false +
• Enzyme Linked Immunosorbent Assay (ELISA)
  • Detect antibody. Passive, Active.
  • Sequential testing. False + and False -
• Restriction Fragment Length Polymorphism (RFLP)
  • Characterizes virus groups. Poor test
• Viral Sequencing
  
  • Small portion of genome looked at. Dendograms
  • Value?

Biosecurity

• Biosecurity is probably the most important factor that producers can control to minimize the impact of PRRSV in their system
  • Internal and External
• Down-time for personnel
• Ante-rooms
• Shower-in-shower-out facilities
• Cleaning/Disinfecting facilities
• All-in-all-out pig movement
• Screens/netting/rodent control
• Air filters
• Danish Entry

PRRSV Treatment Considerations

• Antibiotic therapy
  • Macrolide Class will concentrate in PAMs and provide some anti-inflammatory action. Ex=Pulmotil and Draxxin
  • Treat other infections based on Culture/Sensitivity
• Vaccination
  • Protect those not yet exposed
  • Activate Cellular Mediated Immunity. Decreases replication and shedding.
• Anti-inflammatory Drugs
  • Asprin
  • IB Profen
• Interferon

PRRSV: Immunologic Control

• Vaccines
  • Modified Live Commercial products (ATP/ResPRRS)
  • Killed vaccines (clinic/autogenous)
  • Subunit vaccines (MJ PRRSV)
• Natural Exposure
• Serum Therapy
  
  • Incoming gilts
  • Whole herd
  • Mid-gestation

PRRSV Research: What's new?

• Transmission of PRRSV via aerosal.
• Length of viral shedding in infected animals.
• MLV use during disease outbreaks
• New Highly pathogenic strain characterized

PRRSV: Aerosol Transmission

• This route has always been suspected, but was very difficult to prove.
• University of Minnesota has been looking into this method very intently.
• Trial at UM was designed as follows:
  • 4 barns: 1 infected, and 1 low biosecurity, 1 medium biosecurity, and 1 high biosecurity 120 m from infected
  • Repeated trial 26 times in 2 week incriments 

Aerosol results

• Low level of biosecurity (no intervention) resulted in a high rate of infection.
• Medium level of biosecurity: showering but no air filters= 8/26 infected.
• High level: showering and air filters resulted in no infection.
• The best times for infection were cool/cold days, with mild prevailing winds, high humidity, and low UV index.

Length of PRRSV shedding

• Study at ISU inc3luded 109 pigs infected with PRRSV at 3 weeks of age.
• Results from the trial included:
  •  Peak viremia was between 7 and 21 DPI
  • Most pigs cleared the virus by day 42
  • Occasional positive animals (2-7%) through 154 DPI. Intermittently shedding.
  • Lymphoid tissues remained positive through 202 DPI.
• The virus persisted in the population longer than previously thought.
• Virus likely sequesters in lymphoid tissues, and reappears during times of immune-stress
• These results make us re-think
  • Isolation times
  • Purchasing animals from previously positive herds
  • What it takes for a herd to consistently produce negative iso-weans.

New Use for PRRSV MLV?

• UM study looked for alternative ways to use the MLV products already on the market in G/F pigs.
• Vaccine administered at 1 week after PRRSV infection. Some pigs were then infected with a different highly pathogenic strain 98 days afte the first infection.
• The objective was to study the therapeutic effects of vaccine intervention and prevention of re-infection.
• Vaccine did not produce sterilizing immunity.
• Vaccination did not prevent re-infection
• Vaccine did reduce viral shedding.
• Vaccination was able to decrease the clinical impact of disease.
• The success of this intervention would likely vary depending on the strain of PRRSV that your pigs are challenged with.