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December 2006 Issue

Enzootic Bovine Leukosis Virus (BLV):
Surveillance and Eradication

What is Bovine Leukosis?
Enzootic Bovine Leukosis is a blood-borne disease of adult cattle that is caused by the bovine leukosis virus (BLV). Most infections are subclinical; approximately 30% of infected cattle over three years old develop lymphocytosis; a smaller proportion (about 0.1 to 10%) develop lymphosarcomas. Cattle with tumors almost always die suddenly, or within weeks or months after developing clinical signs. Signs depend on the location of the tumors and may include anorexia, anemia, weight loss, decreased milk production, digestive disturbances, diarrhea, heart failure, posterior paralysis, and exophthalmos.

The Economic Impact of BLV
BLV affects both beef and dairy cattle, but is more prevalent in dairy herds. Milk and meat producers suffer economic losses from the death of cattle with tumors, loss of milk production, replacement costs from early culling, costs of treatment and diagnosis, and the condemnation of carcasses at slaughter. Concern about the spread of BLV is increasing within the world market, prompting governments to enact surveillance programs for enzootic bovine leukosis. Increasingly, presence of the disease worldwide limits international trade as BLV-free countries will not buy infected animals, and require regular testing of domestic herds.

Enzootic bovine leukosis occurs worldwide, mainly in America, Australia, Eastern Europe and Asia. BLV-eradication campaigns have been implemented in most European countries, the United States, Australia and other countries. European Community states such as Belgium, Ireland, Norway, Austria, Germany, Sweden and the Netherlands are free of BLV.

The Bovine Leukemia Virus
BLV is a retrovirus of 80–100 nm that is structurally related to human T-lymphotrophic viruses 1 and 2 (HTLV-1 and HTLV-2). The virus targets the B-lymphocytes where the proviral DNA integrates at random into the nuclear DNA of the host cell. The virus particle consists of single-stranded RNA, nucleoprotein, p12, capsid (core) protein p24, transmembrane glycoprotein gp30, envelope glycoprotein gp51 and several enzymes including reverse transcriptase. Virus is cultured in vitro by co-cultivation of lymphocytes and an indicator cell line through stimulation with mitogens. The gp51 protein appears early in infection and antibodies to the protein can be detected by ELISA tests.

Diagnosis
Animals with clinical signs of the disease have palpable enlarged lymph nodes and tumors. However, clinical signs are not often present.

If clinical disease is not present, BLV is diagnosed by AGID (Agar Gel Immunodiffusion) or ELISA (Enzyme Linked Immunosorbent Assay) tests that detect the level of BLV antibodies in serum and milk. Infection with the virus gives rise to an antibody response. Antibodies in blood appear within 3 to 16 weeks after infection.

• ELISA tests for serum or milk samples are sensitive and can be used with pooled samples.
• The AGID test is specific, but not very sensitive in detecting antibody in individual animals. It is unsuitable for milk samples because it lacks specificity and sensitivity.
• PCR (Polymerase Chain Reaction) is a very quick and sensitive means of identifying BLV provirus in individual animals, but is not suitable as a herd test. PCR is used as an adjunct to serological testing for confirmation.

The CHEKIT* Leucose Serum Antibody ELISA Test Kit
The CHEKIT* Leucose Serum Antibody ELISA test kit detects antibody in serum and plasma with only 10 microliters of sample. It can test individual or 10 pooled sera samples, with the same incubation conditions for samples and conjugate.

The IDEXX CHEKIT Leucose Serum Antibody Test Kit offers high specificity, which reduces the need for verification with adjunct testing. Antigens are produced by a new cell line producing antigen that is free from other viruses, providing greater specificity and reducing false positives. The international reference sample E4 scores positive at a dilution of 1/10 (single samples) and 1/100 in a pool of 10 individual samples.

The test meets OIE prescriptions and EU directives for sensitivity (OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals) and Annex G to EEC directive 88/4/06/EEC. As worldwide concern about BLV grows, eradicating and preventing spread of BLV is accomplished through testing and surveillance. The CHEKIT* Leucose Serum Antibody ELISA Test Kit provides a fast, easy and accurate way to meet testing and eradication directives.

IDEXX Laboratories, Inc. is pleased to announce that the certification of Dr. Bommeli AG has been renewed. Bommeli Diagnostics was originally ISO9001–2000-certified in 1996 for the development, production, and distribution of in-vitro diagnostics for epidemiologically relevant animal diseases which have economical importance or can threaten human health. The recently received certification is valid through August of 2008.

Located in Bern, Switzerland, the facility encompasses more than 1500 square meters and houses all the departments necessary to produce, distribute and offer state-of-the-art ELISAs: Research and Development, Production, Quality Control, Packaging, Sales, Marketing and Technical Support.

The New IDEXX CHEKIT* CAEV/MVV Antibody Test Kit
Caprine Arthritis/Encephalitis (CAEV) and Maedi-Visna (MV)

Caprine Arthritis/Encephalitis (CAEV) and Medi-Visna (MV) are persistent diseases that are caused by closely related lentiviruses. In both sheep and goats, the primary mode of transmission of the virus is through the colostrum or milk during nursing, requiring producers to remove newborns from infected mothers.

Clinical Signs
In sheep, clinical MV disease is characterized by labored breathing and emaciation. “Maedi” is an Icelandic name that describes the labored breathing that is caused by interstitial pneumonitis. “Visna” refers to the “wasting” sign associated with paralyzing meningoencephalitis. Ovine lentiviruses are found in all of the sheep-rearing countries of the world except Australia and New Zealand.

In goats, CAEV virus causes chronic arthritis, bursitis and synovitis. Encephalitis occurs in kids between 2 to 6 months old after infection.

Both infections are associated with indurative mastitis, which is thought to have underestimated economic significance. Because many infected animals do not show clinical signs, serological testing is necessary to confirm the presence of seropositive individuals and to screen herds for the disease. Many surveillance programs require producers to test herds once a year to maintain CAEV and MVV-free status.

Diagnosis
Serological tests for antibodies to the CAEV/MVV viruses include AGID and ELISA. Both are prescribed by OIE for international trade. The sensitivity and specificity of both tests depends on the quality of the antigen. IDEXX has developed a test with a high quality antigen that has both a high sensitivity and an excellent specificity for detecting lentivirus antibodies in serum and milk.

The IDEXX CHEKIT* CAEV/MVV Antibody Test Kit
In September, 2006, IDEXX announced a new CHEKIT* CAEV/MVV Antibody Test Kit. It replaced the previous CAEV/MVV Antibody Test Kit with slightly increased sensitivity and the same excellent specificity for improved overall performance. The new test version is easier to work with. Conjugate, substrate and stop solution are ready for use. The insert provides you with information about preparations, precautions, a detailed protocol and a summary of the test procedure for your convenience. Make sure you read the plates at 450nm.

If you have a question about the performance of an IDEXX test kit, your IDEXX representative requires certain information in order to help you. Your answers to the questions such as these help us to quickly diagnose the performance issue:

• What is your company name and phone number?
• What test kit are you using?
• What is the batch or serial number of the test kit?
• How many kits of the same batch or serial number do you have?
• What is the performance inquiry regarding? (e.g., unexpected results, invalid plate)
• Can you provide the data to illustrate the problem?
• Have you tested the kit more than once and did it show the same problem?

When calling your representative with performance questions, please have relevant xChek* and other data available. This information helps us to quickly gather the information that we need. We appreciate your help in providing descriptive information and data that will help resolve your question quickly.

Events around the world

• Atlanta, Georgia USA—January 24–26, 2006
  International Poultry Expo (IPE)
• Nashville, Tennessee USA—January 31–February 3, 2006
  National Cattleman Beef Association (NCBA)

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IDEXX Product information is also available in German and Spanish (Latin American).

*HerdChek, CHEKIT 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.