Porcine Reproductive & Respiratory Syndrome Virus (PRRSV) Quantitative PCR

Item No.  856

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Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a virus that causes potentially severe disease in swine with significant economic consequences for producers. There are two major strains of PRRSV, one primarily found in North America (U.S. strain), and one primarily prevalent in Europe (E.U. strain). Although they are genetically quite distinct, infection with both strains exhibits very similar clinical signs, which include respiratory, pneumonia-like symptoms and reproductive complications in sows.

The industry is primarily effected by the reproductive issues that are caused by the virus. Late-term abortion, stillbirths, mummifications, and fetal deaths during pregnancy occur with 35-50% of piglets. Piglets born alive are generally weak and the mortality of live-born piglets is 50-100% in most litters. Sows infected with PRRSV show a slow return to service. This on average, costs the swine industry $644 million annually, mostly due to loss of litters.

It is, therefore, an industry standard to test animals prior to shipping and to test boars prior using their semen. Additionally, routine surveillance of production sites is part of health and wellness management. The VDX offers same-day turnaround time to facilitate timely shipping and transport of live animals, and use of boar semen the same-day to maintain optimal semen quality and fertility.

Detection of the PRRS virus: Polymerase Chain Reaction (PCR) is an extremely accurate, sensitive, and fast method to detect the presence of the PRRS virus in a wide variety of sample types. Potential sample types include serum, ear stick, oral fluid, raw semen, and environmental samples.

Utilization of an internal PCR control target in every reaction ensures that no PCR inhibition has taken place and negative results can be reported with confidence. In addition to the qualitative test that determines whether a virus is present, the VDX also offers a quantitative PCR test that will accurately estimate the number of PRRS virus particles in the sample.

Species Porcine
Submission Information Acceptable Sample Type: Serum
Turnaround Time As needed




What is the turnaround time?
PRRSV PCR carries a same-day turnaround time. The test is run Monday through Friday and results will always be sent before the end of the day.

PRRSV ELISA generally carries a next-day turnaround. If same-day results are required, please talk to the lab prior to submitting samples so arrangements can be made.

How late can samples be received and still get same-day results?
In order to receive the same-day turnaround for the PRRSV PCR, samples should be received by 2:00 pm.

What is a PCR?
PCR is an acronym for polymerase chain reaction. PCR is a method used in molecular biology to amplify a single copy, or a few copies, of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence. In a real-time PCR, which is utilized at the VDX, the detection of the amplification is accomplished by a fluorescent dye that is released when amplification takes place and is detected by the real-time PCR instrument. The PCR method cannot determine whether virus detected in a sample is alive or dead.

What is an ELISA?
ELISA is an acronym for enzyme-linked immunosorbent assay. It is a method for identifying antibodies or antigens in a sample. This is accomplished by using a plate that has its wells coated with antigen or antibody that the desired target is able to bind to. The PRRSV ELISA is an antibody ELISA, so the plate wells are coated with PRRS virus. In order to detect the bond between antibodies in the serum sample and the PRRSV in the well, a peroxidase reaction has to take place. This reaction, when positive, causes a color change in the well. The amount of color is read by the ELISA instrument as "optical density" and the values are calculated against a standard to determine whether the sample is antibody positive or antibody negative.

What kind of environmental samples can be received?

  1. Swiffer (must be unscented)
  2. Liquid (such as pit or lagoon samples)
  3. Material collected on swabs

How are results reported?
PRRSV PCR test results are reported as CT (cycle threshold). The CT number is a number relative to the amount of virus in the sample. The closer the number is to 1 (or the smaller the number is), the more virus is present in the sample. Neogen's LIMS system formats the report such that both the CT and the final diagnosis is reported.

The quantitative PCR is expressed as virus titer in copies of virus per milliliter.

PRRSV ELISA is reported as an S/P ratio (sample/positive). The S/P ratio is calculated using the raw optical density (amount of color) determined by the instrument, normalizing the sample to a blank, then dividing by the positive control. The higher the S/P ratio the more antibodies were present in the sample.

All results are reported as pdf files, attached to an email.

What is the difference between the qualitative multiplex PRRSV PCR and the quantitative US PRRSV?
The qualitative multiplex PCR will test for both the U.S. and E.U. strain of PRRSV. This test will not give a virus quantity but will tell whether a virus was present in the sample. Results are expressed as a CT.

The quantitative PCR only tests for the U.S. strain of PRRSV. The test utilizes a standard curve of known virus quantities that, in comparison to the sample, allows to estimate the amount of virus genomes, and thereby virus particles, present in the sample.