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Laboratory diagnostics: Parvovirus

What laboratory diagnostic methods can I use to diagnose parvovirus? Which one should I choose according to the situation? How do I interpret the results?

Assays available:

Immunofluorescence antibody (IFA)

  • Detects presence of viral antigen
  • Sample types: tissues (aborted or mummified fetuses)
  • Pros:
    • Detects virus in aborted or mummified fetuses (good proof of causation).
    • Any positive result is considered significant.
  • Cons:
    • Some mummified tissues are too decomposed to detect virus.
    • Requires significantly more virus to be present than PCR.
    • Often virus infection occurred several weeks prior to abortion or delivery of mummified fetuses.

Polymerase chain reaction (PCR)

  • Detects presence of specific sequence of viral nucleic acid (DNA)
  • Sample types: tissues
  • Pros:
    • High sensitivity.
    • Moderate cost
      • Can often do pooling of tissue samples to lower cost while minimizing loss of sensitivity (especially regarding clinical relevance).
  • Cons:
    • Requires tissue samples from aborted or mummified fetuses for best results.
    • Some mummified tissues are too decomposed to detect virus.

Enzyme-linked immunosorbent assay (ELISA)

  • Detects presence of antibodies
  • Sample types: serum
  • Pros:
    • Animals remain positive for several months to years
    • Able to test large number of animals
    • Vaccinated animals produce significantly lower antibody levels compared to field infections
    • Only takes 6-10 days to become seropositive
  • Cons:
    • Seroprevalence is high as pathogen is common
    • Some ELISAs can differentiate vaccine from wild type virus exposure
      • Inactivated vaccines only stimulate antibodies to structural proteins (VP1/VP2)
      • Differential ELISA targets non-structural proteins (NS)

Hemagglutination Inhibition (HI)

  • Detects presence of antibodies
  • Sample types: serum
  • Pros:
    • Animals remain positive for several months to years
    • Higher sensitivity than ELISA (can detect lower concentration of antibodies)
    • Vaccinated animals produce significantly lower antibody levels compared to field infections
      • Vaccine usually ≤ 1:500
      • Field infection ≥ 1:2000
    • Animals test seropositive as soon as 6 days post infection
  • Cons:
    • Not feasible for large number of samples.
    • Reliability is highly dependent on technician skills.
    • Reactivity is dependent on incubation temperature.

Result interpretation:

IFA

  • Positive: Virus is present in fetus
  • Negative: negative or infection occurred early in pregnancy and too late or tissue too decomposed to detect virus

PCR:

  • Positive: Virus is present in fetus
  • Negative: negative or infection occurred early in pregnancy and too late or tissue too decomposed to detect virus

ELISA (differential ELISA)

  • Positive:
    • Low values past exposure (>6 days) to vaccine
    • High values: recent exposure to wild-type virus
  • Negative: Negative or wild-type infection too early to detect.

HI

  • Positive:
    • Low values past exposure (>6 days) to vaccine
    • High values: recent exposure to wild-type virus
  • Negative: Negative or wild-type infection too early to detect.

Scenarios:

Sow herd with infertility and mummified fetuses

  • Collect 4-8 fetuses (target mummified fetuses) and pool samples for PCR testing.
  • Aborted sows/gilts: Collect serum from affected
    • If HI titers are ≥ 1:2000 – confirm recent viral infection
    • Otherwise retest in 2-4 weeks and compare titers over time looking for > two-fold increase
Infertility and mummified fetuses due to parvovirus
Infertility and mummified fetuses due to parvovirus

Sow herd with infertility and NO mummified fetuses:

  • Collect serum from affected and normal sows today and retest same animals in 2-4 weeks
    • If HI titers are ≥ 1:2000 – confirm recent viral infection
    • Otherwise compare titers over time looking for > two-fold
  • Evaluate parity distribution of affected animals
    • Parvovirus infection is more common in 1st or 2nd parity animals as older parity animals are more likely to already have protection.

See the "Disease manual" for more information

Porcine parvovirus infectionParvovirus affects mainly non-vaccinated primiparous sows, causing reproductive problems such as mummies.

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