• Eradication of pestivirus infection in Austrian cattle—Ear-notch sampling as a long-term perspective
  
  
• IDEXX Announces BSE Short Protocol Test—the fastest microtiter-based test available
  
  

• IDEXX recommends using in-house controls to monitor your ELISA results and kit performance over time.
  
  

• Visit us at these upcoming events

The virus crosses the placenta in infected pregnant cows, causing reproductive losses due to abortions, stillborn calves or calves that die early in life. In addition, when cows become infected between days 30 and 150 of gestation, some calves survive and are persistently infected (PI) animals that are immunotolerant to the virus. These PI cattle are the main source of BVDV transmission, producing and excreting large amounts of virus. As a result, eradication programs are focused on the elimination of PI cattle and preventing the transmission of BVDV to other healthy cattle in the herd.

Motivated by the economic impact of the disease, many countries have initiated BVDV eradication and control programs. IDEXX Laboratories has developed a set of diagnostic tools for detection of BVDV antigen and antibodies. The use of these standardized, highly sensitive and specific, user-friendly HerdChek* BVDV diagnostics have helped veterinarians and farmers worldwide to successfully control BVDV.

Ear-notch tissue samples are rapidly becoming the preferred sample type for diagnosis of persistent BVDV infection. Ear-tissue samples can be easily obtained by farmers or veterinarians without the additional costs associated with blood sampling. In the United States, “ear notchers” are used for the collection of 1-cm-diameter ear-tissue samples for use with the IDEXX HerdChek* Bovine Viral Diarrhea Virus Test Kit (an antigen ELISA test).^† In Europe, a protocol has been developed that combines cattle ear-tagging with the sampling and testing of 2-to-3-mm-diameter ear-tissue samples for BVDV with the IDEXX HerdChek* BVDV Antigen Serum Plus ELISA Test Kit.^‡

The following article demonstrates an integrated control program in the Tyrol region of Austria based on identifying and culling BVDV PI calves using ear-notch samples analyzed on the IDEXX HerdChek* BVDV Antigen Serum Plus ELISA Test Kit. It provides a good example of integrating animal identification and diagnostic testing into an effective control program. The article is adapted from an oral presentation by Dr. Karl Schöpf at the 6th European Society for Veterinary Virology Pestivirus Symposium in Thun, Switzerland, in September 2005.¹

For more information on testing ear-tissue samples, contact your local IDEXX representative.

Introduction

Persistently infected (PI) animals with bovine viral diarrhea virus (BVDV) are the main source for maintaining pestivirus infection in cattle herds. Austria's cattle population consists of about 2.05 million animals, dominated by the breed Fleckvieh, followed by Braunvieh and Grauvieh.

In Austria, a nationwide BVDV control program without the use of vaccines began in 2004, based on the culling of PI animals and the determination of immune status at herd level. A collective control program based on voluntary participation had already been introduced in Tyrol by the end of 1999. Due to annual screening and culling, the prevalence of PI animals declined from 1.22% in 1999 to 0.12% by 2004. Commercial ELISAs were used for screening. In 2004, RT-PCR was introduced for the first time in the laboratory, using pooled plasma blood samples.

In the course of the 2004 testing program, a total of 10,845 herds with 45,872 animals were screened within three months. A total of 93 PI animals were detected in 47 herds. When approaching final clearance of a regional herd, such as in Tyrol, significant delays can easily be suffered if any herd owners are allowed to not clear their herds.

Assessing the prevalence and dynamics of BVDV infection in Tyrol, it is evident that the main source of infection are alms, mountain pastures where cattle herds coexist in close proximity. A second source of infection is trade with young stock. Taking into account the structure of animal production, including cattle density and husbandry practices in Tyrol, it is feasible to concentrate on the traceability of BVDV-tested offspring.

Skin biopsies have been demonstrated to be a useful alternative sample matrix for the in-vivo diagnosis of PI animals. In validation studies, we could prove that there was low interference with maternal antibodies during the colostral period. In 2005, the testing and culling program was changed to antigen testing on farm level of ear-notch samples combined with spot serological antibody testing, from five young heifers older than six months. Every calf in the age group of one week to six months was ear-tagged and tested for BVDV using a commercially available integrated ear-tagging and tissue-sampling system. A total of 34,512 ear-notch samples were analyzed in the laboratory using the IDEXX HerdChek* BVDV Antigen Serum Plus ELISA.

Animals participating in this screening program originated from over 10,000 farms. Final results and possible consequences for implementation of ear-notch testing in BVD control programs are discussed.

Overview of cattle population in Tyrol

The Tyrol region has a total bovine population of 182,740 head in 10,400 herds. Table 1 provides a summary of age distribution of herds, and Table 2 shows the total population by breed. Average herd sizes range from seven to 24 in the nine production districts within the Tyrol region, with an overall average of 17 animals per herd.

Characteristics of animal husbandry in Tyrol

Pasturing cattle on community alms, or mountain pastures, during the summer grazing period is a common practice, with nearly 60 percent of the total cattle population in the region placed on alms. Table 3 provides additional detail on age and presence of other species. Figure 1 shows the location of the 2,600 alms, representing 6,000 square kilometers, throughout the Tyrol region. In addition, trade of young stock is prevalent within the region, with 69 auctions taking place in 2005, where young stock is traded among farms.

History of BVDV diagnostics testing in Tyrol

By the end of 1999, a collective control program based on voluntary participation was initiated in Tyrol. Starting in 2003, it was necessary to test over 45,000 blood samples for antigen and antibody in a very short period of time. This level of testing was achieved through a cooperative effort between the AGES veterinary laboratories in Linz and Innsbruck. In 2005, for the first time in Austria, over 34,500 ear-notch samples from Tyrol's cattle were tested for BVDV antigen. Specific details are summarized in Table 4 and Figure 2.

Compulsory control program

In August 2004, Austria established a compulsory national BVDV eradication program without the use of vaccines, based on culling of PI animals and the determination of immune status at herd level. BVDV is now a notifiable disease throughout Austria.

Under the program, herds are classified in the following three categories:
• BVDV-free herds—not infected
• Presumed not virus-free herds—BVDV infection suspected
• BVDV-infected herds

The program utilizes a range of diagnostics tests, outlined in Table 5, to assess BVDV infection on a farm level and on an individual animal basis. In Tyrol, identification of PI animals for culling is based on ear-notch tissue samples. The tissue samples are obtained utilizing a commercial ear-tagging system with an attached sampling device. The samples are then analyzed in the laboratory using the IDEXX HerdChek* BVDV Antigen Serum Plus ELISA.

Results

Results under the compulsory control program are presented in Tables 6 through 8 and Figures 3 and 4.

Conclusions

• The BVDV Control Program in Tyrol is community-based and uses a combination of diagnostic tools.
• Traceability is very important due to characteristics of animal husbandry within the region.
• Ear-notch sampling helps to identify negative animals and mark them permanently.
• Monitoring of infected herds is strictly enforced by district veterinarians.
• Prevention of new infection is achieved by close monitoring and testing of all cattle intended for trade.
• No use of vaccination.

Notes:
^†Available in the U.S. only
^‡Available from IDEXX Europe only

1. Schöpf K, Matt M, Dünser M, Schweighardt H. Presented at: 6th European Society for Veterinary Virology Pestivirus Symposium. September 2005, Thun, Switzerland.
2. Commercially available BVD-antibody ELISA

IDEXX Laboratories is pleased to announce that the IDEXX HerdChek* Bovine Spongiform Encephalopathy Antigen Test Kit received USDA and EU approvals for its new short protocol. This shorter protocol allows users to complete the assay in less than 2.5 hours. This makes the IDEXX BSE Test Kit the fastest microtiter-based test available.

Nevena Djuranovic, TSE marketing manager, states, “Many TSE laboratories have already found the benefits of the IDEXX HerdChek* BSE Test Kit’s ease of use and efficiency. The test’s prion-capture technology eliminates the need for complicated proteinase K sample preparation. We’ve further improved the test by reducing the sample and conjugate incubation times to as little as 45 minutes each. That’s one-and-a-half hours saved.”

The IDEXX HerdChek* Bovine Spongiform Encephalopathy Antigen Test Kit is an antigen-capture enzyme immunoassay (EIA) for detection of the abnormal conformer of the prion protein (PrP^Sc). The kit detects abnormal prions from postmortem brain tissue from cattle with BSE. The kit is intended for veterinary use only.

IDEXX recommends using in-house controls to monitor your ELISA results and kit performance over time.

We recommend formulating a control that is similar to the sample-to-positive (S/P) or sample-to-negative (S/N) ratio of the samples that you want to monitor. Laboratories can use prediluted controls or dilute the controls each time they run an assay. Undiluted controls should be thawed, mixed and diluted in the same manner as a routine sample. Prediluted controls are ready to use and can be added to the plate after thawing and mixing. A prediluted control can be helpful as it eliminates potential dilution problems as a concern when analyzing results. Either control should be run on every plate that is assayed in the laboratory.

If you are using the IDEXX xChek* software to maintain ELISA data records, you can easily track your internal control results. IDEXX suggests creating a unique case name for your internal control so you can easily recall results and evaluate your data over time. Any variations or trends should alert you to review your technique and quality-control measures.

If you have any questions regarding internal control formulation or use, contact your local IDEXX representative.

LEARN MORE

To learn more about our products and services, innovative technologies, trusted service and support, and our global offices, visit our Web site.

VISIT US AT THE FOLLOWING EVENTS

Sydney, Australia—February 20–22, 2006
Australian Poultry Science Symposium

Göttingen, Germany—February 24–26, 2006
AVA Haupttagung (Rind + Schwein)

Kansas City, Missouri USA—March 4–7, 2006
American Association of Swine Veterinarians (AASV)

Sacramento, California USA—March 5–8, 2006
Western Poultry Disease Conference (WPDC)

Bangkok, Thailand—March 8–10, 2006
VITAM

Galloway, New Jersey USA—March 13–15, 2006
NEUSAHA

Radenci, Slovenia—March 29–April 2, 2006
7th Middle EU Buiatric Congress

WE WANT TO HEAR FROM YOU…

...and we want you to hear from us! Pass the following link along to your friends and colleagues. They can register for Animal Health Updates to stay informed of the latest IDEXX products and services and respond to various customer and market surveys. Registration is easy at www.idexx.com/production/livestockpoultrynews.

Questions or comments?

*HerdChek and xChek are trademarks or registered trademarks of IDEXX Laboratories, Inc. in the United States and/or other countries. All other product and company names are trademarks or registered trademarks of their respective holders.

This symbol indicates PDF-formatted materials. To view, you may need to download a free copy of Adobe^® Reader^® software.