PRRSPRRS Porcine Respiratory and Reproductive Syndrome Dr. Alex
Ramirez Veterinary Diagnostic and Production Animal Medicine Iowa
State University
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PRRSPRRS General Overview
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PRRSPRRS 3 PRRS THE most $$$ significant disease of swine $560
million / year $5.60 / pig marketed 1 Comparison PRV $36 million /
year Hog cholera $360 million / year Outbreak estimated cost of
$255 / sow 2 Continues to be a widespread cause of abortion and
respiratory disease in Iowa and the United States 1 Neumann et al
2005 2 Holck and Polson 2003
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PRRSPRRS 4 Karriker et al
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PRRSPRRS 5 Relatively easy to do Karriker et al
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PRRSPRRS 6 Relatively easy to do Hard to maintain Karriker et
al
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PRRSPRRS 7 Characteristics of the Virus RNA virus High mutation
rate Enveloped Does not survive well in the environment Likes cold
weather Open Read Fragments (ORF) Total of eight (1a, 1b, 2, 3, 4,
5, 6, 7) Usually only sequence ORF 5 Sequencing 600 bp (4%) out of
~15,000 bp
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PRRSPRRS 8
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PRRSPRRS 9 Characteristics of the Virus Constantly changing
Quasi-Species European versus American strains only 60-70% similar
Variable expression of disease severity PRRS Lite Acute PRRS new
disease or just a stretch Immunity induced by one strain does not
protect against another strain
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PRRSPRRS 10 Characteristics of the Virus Highly infectious
Takes only a few viral particles to infect a pig Increasing dose
Quicker onset of disease Minimal influence on the ultimate severity
of disease Transmission Potential : Low?? Research not very easy to
spread Field variable experiences Body secretions including semen
Farm-to-farm: neighborhood spread seems to occur
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PRRSPRRS 11 PRRS transmission RouteID 50 SQ (parenteral)~10 1
Intranasal10 3.9 Artificial Insemination10 4.5 Oral10 5.2 Aerosol??
Hermann et al 2005
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PRRSPRRS 12 Duration of shedding Up to 5 months or longer
Experimental studies done in clean animals Mycoplasma prolongs
PRRS-induced pneumonia Does mycoplasma prolong PRRS shedding? Route
Semen Oral secretions Age Younger longer Characteristics of the
Virus
PRRSPRRS 14 Available Tests FATS: Fluorescent antibody
examination of frozen tissue PCR: Polymerase chain reaction RFLP:
Restriction fragment length polymorphism VI: Virus Isolation Virus
sequencing: Sequence analysis IHC: Immunohistochemistry ELISA:
enzyme-linked immunosorbent assay IFA (NVSL): indirect fluorescent
antibody test FFN: fluorescent focus neutralization assay VN: Virus
neutralization
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PRRSPRRS 15 Available Tests FATS: Fluorescent antibody
examination of frozen tissue PCR: Polymerase chain reaction RFLP:
Restriction fragment length polymorphism VI: Virus Isolation Virus
sequencing: Sequence analysis IHC: Immunohistochemistry ELISA:
enzyme-linked immunosorbent assay IFA (NVSL): indirect fluorescent
antibody test FFN: fluorescent focus neutralization assay VN: Virus
neutralization XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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PRRSPRRS 16
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PRRSPRRS Respiratory
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PRRSPRRS 18 PRRSv Diagnostics Lesions Interstitial pneumonia
Can visualize septa - fine pattern Tan discoloration - mottled or
coalescing Rubbery texture Fail to collapse Enlarged lymph nodes
Sub-iliacs are best to view
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PRRSPRRS 19 PRRSv Diagnostics
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PRRSPRRS 20 Low virulent strain of PRRSv High virulent strain
of PRRSv
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PRRSPRRS 21 PRRSv-infected alveolar macrophages PRRSv-infected
intravascular macrophages PRRSv infects and destroys macrophages in
the lungs. Macrophages are important for removing bacteria and
inflammatory debris from the lungs.
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PRRSPRRS 22 All strains of PRRSv induce lymphadenopathy
characterized by hyperplasia of lymphoid follicles
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PRRSPRRS Reproductive
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PRRSPRRS 24 Gestation age Animal response Weak born pigs
Stillborn pigs Mummies Early embryonic death reduced litter size
Return to estrus Abortion Boars Shed in semen Variable impact on
semen quality Clinical Outcomes
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PRRSPRRS 25
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PRRSPRRS 26 PRRSv - Abortion due to Fetal Infection Gross
Lesions: Sow: typically none Fetus: Diagnostically useful gross
lesions are uncommon Meconium staining of fetal skin Umbilical cord
edema with segmental hemorrhage Mesocolonic edema Perirenal
edema
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PRRSPRRS 27 PRRSv-Infected Fetuses
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PRRSPRRS 28 Distribution of PRRSv-Infected Fetuses in a Litter
ALL FETUSES IN A LITTER ARE TYPICALLY NOT INFECTED An average of
48.6% of the fetuses/litter infected Sow 10 PRRSV-POSITIVE Fetuses
1, 2, 3, 4, 6 (#5 autolyzed) PRRSV-negative fetuses 7, 8, 9, 10,
11, 12, 13 Sow 12 PRRSV-POSITIVE Fetuses 5, 6, 7, 8, 9, 10
PRRSV-negative fetuses 1, 2, 3, 4, 11, 12
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PRRSPRRS 29 Assumptions: Litter of 12 50% fetal infection rate
Confidence level for PRRSV detection in a litter with PCR Number of
fetuses sampled per litter 99%6 97.5%5 95%4 90%4
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PRRSPRRS 30 PRRSV Abortion Diagnostics PCR is the test of
choice on fetal material Extremely sensitive Tissues and fetal
thoracic fluid are equivalent Samples from 1 positive fetus can be
pooled with 7 negative fetuses (1:8) without loss of sensitivity
Limited impact of autolysis (can be detected following incubation
at 37 o C [99 o F] for 4 days) Preferred diagnostic procedure: pool
fetal thoracic fluid from 6 fetuses/litter for PRRSV PCR
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PRRSPRRS 31 Clinical Outcomes Suckling and nursery pigs Severe
respiratory disease: interstitial pneumonia Rapid breathing,
especially after stress Variable death loss Often takes 30-45 days
longer to reach market compared to groups ahead or behind Severity
of infection diminishes greatly after 8 weeks of age unless
affected by another agent M. hyo PCV2 SIV
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PRRSPRRS Vaccination
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PRRSPRRS Zuckermann, 1999 ParameterPRRSVPRV.
Non-neutralizing7-14 daysNA antibodies Neutralizing antibodies>
28 days3-4 days Peak gamma 8-10 months1 month interferon levels
Duration of shedding> 3-4 months3-4 weeks PRRSV Immunity
Development
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PRRSPRRS 34 CONTROVERSIAL (to say the least!!) Everyone has a
different opinion MLV vaccines Several have been marketed Patent
infringement has resulted in only two available today: Boehringer
Ingelheim PRRS MLV PRRS ATP Variable benefit Strain differences
Delay between vaccination and protective immunity need at least 4 6
weeks Vaccination
PRRSPRRS 36 Vaccination Sequence information Does not predict
virulence Does not predict respiratory vs. reproductive Does not
predict cross-protection Do not use to select best vaccine Does
help as a epidemiological tool New vs. old Possible source? Does
serve as a reference for the future
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PRRSPRRS 37 PRRSV Vaccination Killed vaccines None commercially
available today Appear to booster existing immunity Unclear
efficacy in nave animals Most likely of no value Autogenous?
Quasispecies Stability
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PRRSPRRS 38 Based on the concept that the virus is shed 4-6
months after infection Infect/vaccinated incoming animals >3-4
months before entry Stop animal introductions for 4-6 months, then
start introduction of negative animals Gilts most likely to
transmit virus to their offspring Many programs developed off this
strategy Produce PRRSV free offspring from sow herd Eliminate PRRSV
reproductive failure Eradicate PRRSV without depop-repop Serum
Inoculation
PRRSPRRS 41 Acknowledgements I would like to recognize the
contribution of others to this presentation: Dr. Brad Thacker Dr.
Locke Karriker Dr. Pat Halbur
