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HerdChek* Porcine Reproductive and Respiratory Syndrome Test Solutions

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December 2009 Issue

Overview of Porcine Reproductive and Respiratory Syndrome (PRRS)

PRRS is an arterivirus first reported in both Europe and the U.S. in the late 1980s as distinct strains with variable antigenicity.¹ The North American strain varies significantly from the European (EU) strain (also referred to as the Lelystad strain) at both the antigenic and genetic levels, having only 60% nucleic acid identity with the EU strain.²

The virus causes reproductive problems (abortions, weak piglets, failure to farrow, and sow deaths), respiratory disease (pneumonia, difficulty breathing, poor performance, and death) and mild neurologic signs.¹ PRRS is considered to be one of the most economically significant diseases affecting the swine industry.

PRRS virus outbreaks have been frequent in swine producing countries. Outbreaks cause significant losses in swine productivity and in financial outcomes. Frequent monitoring of infection status is commonly done by serological testing.

Measuring PRRS antibodies in swine serum is an effective way to assess animals’ exposure to the PRRS virus by natural infection or by vaccination. Prior to the introduction of the new HerdChek* PRRS X3 Antibody Test Kit, the HerdChek PRRS 2XR Antibody Test Kit, a dual-well ELISA, was routinely used for monitoring swine populations for exposure to PRRS infection. Early virus detection, without false positive results, is critical for effective serological testing.

Introducing the New HerdChek* PRRS X3 Antibody Test Kit, with Improved Specificity

PRRS X3
99.9% Confidence
No Compromise

IDEXX is pleased to announce the new HerdChek* PRRS X3 Antibody Test Kit for porcine reproductive and respiratory syndrome (PRRS).

This new indirect enzyme-linked immunosorbent assay (ELISA) detects PRRS antibodies in plasma or serum with 99.9% specificity and 98.8% sensitivity. The test reduces false-positive singleton reactors by 90% and offers a convenient, new, single-well format.

Laboratory Benefits

• Your lab runs more smoothly.
• You don’t need to plan schedules around confirmation tests.
• Your clients trust the results—they know your laboratory delivers definitive answers with clarity and confidence.

Veterinarian/Producer Benefits

• You can move animals with confidence and without delay.
• You’ll almost never need to resample and retest.
• You can accurately establish the farm’s PRRS status; you’ll know with confidence whether PRRS is moving through the herd.
• You can respond quickly to true positive results, to prevent the spread of PRRS.

The PRRS X3 Antibody Test Kit gives laboratories and veterinarians a more reliable and efficient way to accurately diagnose PRRS.

Validation Studies¹

Objective

The primary development goal for the new PRRS X3 Antibody Test Kit was to further improve specificity without compromising sensitivity, as well as to make the test even more user-friendly.

In this study, IDEXX assessed the new single-well-format PRRS X3 test for diagnostic performance on positive and negative samples from populations of controlled infection studies and from general populations of field animals.

Methodology

Multiple European populations were used to evaluate the sensitivity and specificity of the new PRRS X3 test kit.

Positive populations included field exposed and experimentally exposed animals. Negative populations included field negatives and singleton reactors from PRRS 2XR ELISA testing. Serum samples were tested using the PRRS X3 test kit, according to the standard protocol.

Data for these studies were generated at IDEXX Laboratories in Westbrook, Maine. In some cases, samples had previously been tested by indirect fluorescent antibody (IFA) and/or real-time polymerase chain reaction tests at designated diagnostic laboratories from which the samples were sourced and the results provided to IDEXX. Samples that lacked initial IFA test results were not subsequently tested by IFA; PRRS 2XR ELISA results were considered the sole reference method for these samples.

Results

Sensitivity

The PRRS X3 test demonstrated 98.8% diagnostic sensitivity when tested on characterized PRRS-positive field sera samples. There were 233 samples of French origin and 100 sera samples from Ukraine. All samples were from herds characterized as PRRS-positive based on clinical symptoms and on PRRS 2XR ELISA positive results from animals within the herd. The distribution of S/P values resulting from PRRS X3 testing of the entire EU field population is shown in Figure 1.

The PRRS X3 test detected seroconversion as early as eight days post infection (DPI) in populations experimentally infected with the Lelystad virus. Figure 2 shows that the PRRS X3 test detected seroconversion in three animals at eight DPI.

Specificity

The diagnostic specificity of the PRRS X3 test kit was determined to be 99.9% using a population of 749 negative sera. The distribution of S/P values generated from testing the EU negative population on the PRRS X3 test is shown in Figure 3.

A unique population of expected-negative sera, which tested false positive using the PRRS 2XR ELISA (singleton reactors), tested predominantly negative using the PRRS X3 test kit. The PRRS X3 test classified more than 90% of these singleton reactor samples as negative. The distribution of PRRS X3 S/P values generated for the singleton reactors is shown in Figure 4.

Conclusion

The new PRRS X3 Antibody Test Kit for PRRS antibody detection in swine sera delivers unprecedented specificity with reduced risk of false positives, as well as equivalent or improved detection of seroconversion compared to the PRRS 2XR ELISA.

Such a dramatic reduction in the frequency of confirmatory testing means veterinarians can get reliable results more quickly—they can provide faster diagnoses and help their customers make more confident, informed decisions about herd health.

In addition, the single-well format of the PRRS X3 test kit is easier to use and allows more samples to be tested per plate.

The new IDEXX HerdChek PRRS X3 Antibody Test Kit is now available for sale in most countries.†

For More Information

For more information or to order the new PRRS X3 Antibody Test Kit, please contact IDEXX Customer Service at 1-800-548-9997 or 00800-727-43399 (EU), send e-mail to pasweb@idexx.com, or visit www.idexx.com/prrsx3.

Testing with the New HerdChek* PRRS X3 Antibody Test Kit

The new HerdChek* PRRS X3 Antibody Test Kit uses the same test protocol as the HerdChek PRRS 2XR ELISA, with one exception: a single-well format replaces the dual-well format used for the 2XR kit.

Although the cutoff value for the assay remains the same as the cutoff for the PRRS 2XR ELISA, the S/P calculation has changed because a normal host cell is not needed in this test.

Results interpretation requires the addition of a user-defined assay (UDA) to your xChek* software. The UDA requires the PRRS X3 controls to be in the order Neg, Neg, Pos, Pos, which is different from the order used in the PRRS 2XR assay but is the same as that used in most other IDEXX assays.

Download and read the UDA instructions.

Events Around the World

• Marseille, France—December 1–3, 2009
  European Buiatrics Forum
  www.buiatricsforum.com/anpartspons2009.html
• Leipzig, Germany—January 21–23, 2010
  5th Leipzig Veterinary Congress
  www.leipziger-messe.de
• Atlanta, Georgia—January 27–29, 2010
  International Poultry Expo
  www.ipe10.org
• San Antonio, Texas, U.S.A—January 27–30, 2010
  National Cattlemen's Beef Association (NCBA) Cattle Industry Annual Convention & Tradeshow
  www.beefusa.org/convcattleindustryannualconventionandncbatradeshow.aspx

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