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October 2008 Issue

Find, Isolate, Eliminate BVDV

Bovine viral diarrhea virus (BVDV), a member of the Pestivirus genus within the family Flaviviridae, causes one of the most costly diseases for the cattle industry worldwide.

The virus can cross the placenta in infected pregnant cows, causing reproductive losses due to abortions, stillborn calves or calves that die early in life. When pregnant cows become infected between days 30 and 150 of gestation, some calves survive, becoming immunotolerant to the virus. These persistently infected (PI) calves may live two years or longer. PI calves excrete large amounts of virus every day of their lives and are the main source of BVDV transmission. Testing is the only way to identify PI calves.

Diagnosis of persistent BVDV infection using ear-notch tissue samples is a fast, convenient way to detect PI calves before they spread infection. The IDEXX HerdChek* BVDV Ag/Serum Plus Test Kit used with ear-notch tissue samples continues to be a preferred approach in BVDV control and eradication programs worldwide.

The next article, HerdChek* BVDV Ag/Serum Plus, Used with Ear-notch Tissue Samples, summarizes the facts and findings around the use of ear-notch tissue samples in BVDV testing and reports the results of validation studies and other trials for the HerdChek* BVDV Ag/Serum Plus Test Kit.

For more information on BVDV testing, please contact your local IDEXX representative.

HerdChek* BVDV Ag/Serum Plus Test Kit, Used with Ear-Notch Tissue Samples, Is a Preferred Tool in BVDV Control and Eradication Programs

Several types of diagnostic tests can be used to detect bovine viral diarrhea virus (BVDV), including:

• The HerdChek* BVDV Ag/Serum Plus Test Kit, based on detection of the E^rns antigen
• ELISAs based on detection of the NS2/3 antigen
• RT-PCR tests, based on detection of viral RNA

Worldwide validation studies and trials have shown the HerdChek* BVDV Ag/Serum Plus Test Kit to be a superior tool when compared with the other test types, particularly when used with ear-notch tissue samples. Ear-notch sampling is the easiest method for livestock producers to use, requiring no special training for sample collection.

The studies and trials are summarized below.

Recent Study Comparing ELISAs Based on the E^rns Antigen with Other ELISAs

A 2007 study by Robert Fux¹ compared E^rns-based ELISAs with ELISAs based on the NS2/3 antigen.

The Fux study concluded that E^rns ELISAs used with ear-notch tissue samples:


• Show high analytical sensitivity
• Have stable epitopes that are easily released from the sample material
• Have sufficient analytical sensitivity to detect persistently infected (PI) animals of any age
  
  

The study also showed that:


• The sensitivity of NS2/3 ELISAs is too low to safely detect BVDV antigen in dried ear-notch tissue samples of young calves.
• NS2/3 epitopes are relatively unstable when submitted to higher temperatures or certain detergents.
• Detection of NS2/3 epitopes can be completely inhibited in ear-notch tissue of calves with maternal antibodies.

The HerdChek* BVDV Ag/Serum Plus Test Kit is the only commercially available ELISA that detects the highly stable BVDV E^rns antigen^†. The HerdChek* BVDV Ag/Serum Plus Test Kit detects BVDV in ear-notch tissue samples, as well as in blood, serum or plasma.

† Note: The IDEXX HerdChek* BVD Antigen Test Kit, licensed by the USDA and available only in the U.S. and Canada, also detects BVDV E^rns antigens.

Validation Studies Conducted by IDEXX and Others

An ideal BVDV Ag test would have the following characteristics:


• Offer high sensitivity, with no false-negative results
• Have no diagnostic gap caused by interference from maternal antibodies
• Detect all BVDV-1 and BVDV-2 genotypes and all field strains
• Work with reduced-quality samples (dirty or old samples) and after long sample storage

An ideal test would also work with easy-to-collect tissue samples, such as ear notches, and use a familiar ELISA protocol that can be adapted to manual or automated work flows.

The following validation studies demonstrate the effectiveness of the HerdChek* BVDV Ag/Serum Plus Test Kit in meeting the criteria listed above.

Sensitivity and Specificity
The HerdChek* BVDV Ag/Serum Plus Test Kit demonstrated 100% sensitivity and >99.9% specificity in tested populations according to a report by the Animal Health Service of the Netherlands.²

Effect of Maternal Antibodies
Three studies assessed the ability of the HerdChek* BVDV Ag/Serum Plus Test Kit to detect BVDV in the presence of maternal antibodies in young calves. The studies showed virtually no diagnostic gap from maternal antibody interference.

Study 1: Ear-notch tissue samples containing added maternal antibodies (VNT titer 1:32,000) were analyzed using the HerdChek* BVDV Ag/Serum Plus Test Kit. All ear-notch tissue samples were detected as positive.¹

Study 2: Ear-notch tissue samples were tested from 12 PI calves with defined homologous maternal antibody intake. All samples were safely detected as positive.¹

Study 3: Serum samples from three PI calves were tested to determine the effect of colostral antibodies on E^rns Ag detection. The diagnostic gap using HerdChek* BVDV Ag/Serum Plus Test Kit was less than 4 days.³

Genotypes and Strains Detected by the HerdChek* ELISA vs Other Tests
IDEXX tested the HerdChek* BVDV Ag/Serum Plus Test Kit, as well as five commercial PCR tests and three NS2/3 ELISAs, using BVDV field and reference strains. The numbers of correct results for each test type are shown below.

The HerdChek* BVDV Ag/Serum Plus Test Kit detected all strains successfully. All of the NS2/3 ELISAs missed some strains. All but one of the PCR tests missed strains and/or had some weak positive results (Ct >35). Results of the study were presented in a poster at the 7th ESVV Pestivirus Symposium in Uppsala, Sweden, September 16–19, 2008. To order a copy of the poster, please use the online form on the Production Animal Services (PAS) Web site. Enter your request in the message box. Scroll to the bottom of the page, enter your contact information, then click Submit.

Stability and Robustness
IDEXX collected ear-notch tissue samples using all currently available European sampling systems. Samples were stored at different temperatures for 4 weeks and were tested weekly. The HerdChek*BVDV Ag/Serum Plus Test Kit detected positives at 4°C, room temperature and 37°C, even after 4 weeks of storage.

Data on file at IDEXX Laboratories, Inc.

European Ring Trials and Approvals

The HerdChek* BVDV Ag/Serum Plus Test Kit has been used successfully in German and Swiss ring trials and has been approved for use by several European reference laboratories:

• The HerdChek* BVDV Ag/Serum Plus Test Kit was used successfully in ring trials in Germany in 2006.⁴
• Laboratories participating in the Swiss BVDV ring trial in 2007 achieved 100% correct test results using the HerdChek* BVDV Ag/Serum Plus Test Kit.⁵
• The publication of collected methods of the German reference laboratory (FLI) states there is no diagnostic gap for an E^rns Ag ELISA when skin biopsies are tested.⁶
• Germany explicitly registered the HerdChek* BVDV Ag/Serum Plus Test Kit for serum, plasma and EDTA whole blood for:
  
  • Calves before colostrum intake
  • Cattle older than 60 days (2 months)⁶
• The following text from the HerdChek* BVDV Ag/Serum Plus Test Kit insert has been officially approved and registered by state reference laboratories in Germany, Switzerland and Austria:

“When testing ear-notch samples, the diagnostic gap is practically not present.”

The HerdChek* BVDV Ag/Serum Plus Test Kit Is an Effective Tool for BVDV Eradication Programs

The HerdChek* BVDV Ag/Serum Plus Test Kit was used as a screening tool in the Tyrol BVDV eradication program. Over the course of the program, the region showed decreasing antibody and PI prevalence.⁷

Speaking about the Tyrol BVDV eradication program, Dr. Karl Schöpf (Head of AGES Institute for Veterinary Medicine, Innsbruck, Austria) had this to say:

“The HerdChek* BVDV Ag/Serum Plus Test Kit was chosen as the screening test because it is easy to perform, it delivers reliable results and it can be used in newborn and young calves. The diagnostic gap experienced when analyzing blood samples is virtually eliminated when using ear-notch samples with the HerdChek* BVDV Ag/Serum Plus Test Kit.

Over the course of three spring sampling periods from 2005 to 2007, we analyzed a total of 104,020 ear-notch samples from individual calves representing approximately 10,000 farms. Over that period, we saw a decrease in the number of PI animals detected from 84 in 2005 to 32 in 2006 and 11 in 2007.

These results show the great positive effect and benefit of HerdChek* BVDV Ag/Serum Plus Test Kit on our BVDV eradication program. Our technical staff likes to work with this kit because of its simplicity, robustness and reproducibility.”

Features of HerdChek* BVDV Ag/Serum Plus Test Kit

The HerdChek* BVDV Ag/Serum Plus Test Kit:


• Provides results in 4 hours
• Comes with ready-to-use reagents
• Includes bar-coded plates for 100% safe sample identification and traceability
• Can be used with ear-notch tissue samples, blood, serum or plasma
• Uses a simple, familiar ELISA protocol, suitable for manual or automated work flows

The HerdChek* BVDV Ag/Serum Plus Test Kit is a superior BVDV diagnostic and screening tool.

For more information about the E^rns-based HerdChek* BVDV Ag/Serum Plus Test Kit, please contact your IDEXX representative.

Why IDEXX Sends a Survey After Every Support Call

You may have noticed that after you contact PAS Technical Services, IDEXX sends a survey asking about your interaction with the PAS team. Here’s why: IDEXX is certified to ISO standards. Our continued ISO certification depends on monitoring the satisfaction of our customers.

We realize that many of you have close relationships with your IDEXX Technical Services representatives and readily communicate your needs to them, but it is important for us to hear from you through other means as well. That’s why we always send a follow-up survey after our customers contact IDEXX Technical Services.

If you receive an e-mail survey, please take a minute to answer the few questions about your recent experience with PAS Technical Services. Your feedback helps us provide the outstanding products, service and support that you expect from IDEXX.

Events Around the World

• Erice, Sicily, Italy—October 14–17, 2008
  Open Session of the Research Group of EuFMD
• Hall in Tirol, Austria—October 16–17, 2008
  Veterinary Diagnostics for the Practice
• Alghero, Italy—October 22–24, 2008
  Società Italiana di Diagnostica di Laboratorio Veterinaria X Congresso Nazionale (S.I.Di.L.V.)
• Greensboro, North Carolina, USA—October 23–29, 2008
  51st Annual AAVLD/USAHA Meeting
• Lille, France—October 23–24, 2008
  ADILVA 2008
• Colorado Springs, Colorado, USA—November 6–7, 2008
  BEEF Quality Summit
• Hanover, Germany—November 11–14, 2008
  EuroTier 2008
• Killarney, Ireland—November 13–15, 2008
  British Cattle Veterinary Association (BCVA) Congress 2008
• Amarillo, Texas, USA—November 13–16, 2008
  Working Ranch Cowboys Association Ranch Rodeo
• McCook, Nebraska, USA—November 19–20, 2008
  McCook Farm & Ranch Expo
• Springdale, Arkansas, USA—November 21–23, 2008
  Arkansas Cattlemen’s Association Convention
• Amarillo, Texas, USA—December 2–4, 2008
  Amarillo Farm & Ranch Show
• Wichita, Kansas, USA—December 4–5, 2008
  Kansas Livestock Association Convention

Go Green by Going Paperless!

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Sign up today for e-mail or fax delivery of your invoices by contacting Melissa Seader at melissa-seader@idexx.com or by calling (207) 556-8609.

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*HerdChek is a trademark or registered trademark of IDEXX Laboratories Inc. or its affiliates in the United States and/or other countries.