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Appendix C USDA/APHIS DRAFT JOHNE’S DISEASE CONTROL PROGRAM Draft—Uniform Program Standards for the Voluntary Bovine Johne’s Disease Control Program Contents Introduction Part I Definitions and Abbreviations Part II Administration of the Program 1. Designated Johne’s Disease Coordinator A. General B. Qualifications C. Responsibilities 2. State Johne’s Disease Group A. General B. Recommended Members 3. Johne’s Certified Veterinarians
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A. General B. Qualifications C. Responsibilities Part III Program Elements and Procedures 1. Education A. General B. Requirements 2. Management A. General B. Risk Assessment C. Herd Management Plan D. Renewal 3. Herd Testing and Classification A. General B. Requirements for Entrance C. Test-Positive Component (Control and Testing) D. Test-Negative Component (Herd Status) Part IV Laboratory Procedures 1. Approved Laboratories A. General B. Approval Process for Official Johne’s Disease Testing C. Approval Process for Screening Testing 2. Approved Program Tests A. Official Johne’s Disease Tests B. Screening Tests Appendix Table C-1. Herd Subset Sampling
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Introduction This document describes the cooperative State-Federal-Industry Voluntary Bovine Johne’s Disease Control Program, to be administered by the State and supported by Industry and the Federal government. It is intended as a working document that will change as the Program develops. The objective of this Program is to provide minimum national standards for the control of Johne’s disease. The Program consists of three basic elements: (1) Education, to inform producers about the cost of Johne’s disease and to provide information about management strategies to prevent, control, and eliminate it; (2) Management, to work with producers to establish good management strategies on their farms; and (3) Herd Testing and Classification, to help separate test-positive herds from test-negative herds. The Program has been developed in conjunction with the National Johne’s Working Group, with advice and recommendations from the Johne’s committee of the United States Animal Health Association. The Program has been approved by the United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Veterinary Services (VS). The minimum national standards described in this document do not preclude the adoption of more stringent methods and rules by any geographical or political subdivision of the Unites States with regard to activities within their boundaries. However, regulations dealing with interstate movement must still conform to Federal regulations.
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Part I:Definitions and Abbreviations Accredited veterinarian: A veterinarian approved by the Administrator in accordance with the provisions of 9 CFR part 161 to perform functions required by State-Federal-Industry cooperative programs. Administrator: The Administrator of APHIS or any person authorized to act for the Administrator. AIN: American Identification Number: A unique animal identification number consisting of 12 alphanumeric characters plus a 3-character country code. The AIN System is administered through the National AIN Oversight Board. Animal health official: A full time employee of the State animal health department or of APHIS who has authority from the State veterinarian or the AVIC to carry out Program activities. Anniversary date: The date on which the DJC gave final approval for initial Program participation. APHIS: Animal and Plant Health Inspection Service. Approved laboratory: A private, State, Federal, or university laboratory that has passed an annual check test for Johne’s disease administered by NVSL. All Program testing must be done in a laboratory approved by NVSL for the specific test being used in a State’s testing program. AVIC: Area Veterinarian in Charge: The veterinary official of VS/APHIS/USDA, who is assigned by the Administrator to supervise and perform the official animal health work of APHIS in the State or States concerned. CFR: Code of Federal Regulations. Commingling: Physical contact with susceptible species. For example, all cattle grazed together on the same area of a property or farm will be considered commingled. DJC: Designated Johne’s disease coordinator: A person who has demonstrated the knowledge and ability to perform the functions required under these Program standards and who has been selected for this position by the State animal health official and the AVIC. The VS regional Johne’s disease epidemiologist and the VS Johne’s disease staff should concur in the selection and appointment of the DJC.
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ELISA: Enzyme Linked Immunosorbent Assay. Exposure: Contact with known infected animals; contact with the manure or raw milk of infected or exposed animals of susceptible species; or contact with infected herds via contaminated water or feed sources. Herd: A group of animals that has been managed as a separate and discrete unit. This may include two or more geographically separated groups of animals under common ownership or supervision, but which have an interchange or movement of animals without regard to health status. The State animal health official will make the final determination of the herd status of a group of animals. Herd member: An animal of any susceptible species that is commingled with the herd. Herd management plan: A written plan, produced by the certified veterinarian or animal health official in conjunction with the producer, that includes animal husbandry and hygiene practices specific to that herd and that is designed to limit opportunities for exposure to Mycobacterium avium ss paratuberculosis. Infected animal: An animal that has been confirmed by an official Johne’s disease test to be infected with Mycobacterium avium ss paratuberculosis. JD: Johne’s disease: An intestinal bacterial disease caused by Mycobacterium avium ss paratuberculosis. Clinical signs, which appear after a long incubation period, include long-lasting or chronic diarrhea and weight loss despite a good appetite. Johne’s certified veterinarian: An accredited veterinarian who has received training approved by the DJC for Johne’s disease epidemiology and herd management plan development. Known infected herd: A herd in which at least one herd member has been determined to be infected with Mycobacterium avium ss paratuberculosis based on an official Johne’s disease test during the previous 12 months. Level achievement year: The year a herd in the Herd Testing and Classification element of the Program obtained its current classification. Management herd: A herd that has completed a risk assessment and herd management plan that satisfies the requirements of the DJC, but has not completed the requirements for the test-negative or test-positive levels. National AIN Oversight Board: A group that is selected by USDA/APHIS/VS, and that is responsible for selection and retention of Official AIN Administrators and supervision of the AIN System.
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NVSL: National Veterinary Services Laboratories. Official AIN Administrator: Any organization, agency, or private enterprise selected by the National AIN Oversight Board to administer the distribution of Official AIN identification devices. Official AIN identification device: A visual tamper-resistant identification device, such as an eartag, which is issued by an Official AIN Administrator and which bears a unique AIN, the 2-character postal code of the State where the animal is located at the time of identification, and the U.S. Shield. Official eartag: An identification eartag approved by APHIS as being tamper-resistant and providing unique identification for each animal. An official eartag may conform to the alphanumeric National Uniform Eartagging System, or it may bear the valid premises identification that is used in conjunction with the producer’s livestock production numbering system to provide a unique identification number. When the final rule concerning the AIN System is published in the Federal Register, Official AIN identification devices will be used instead of currently used identification systems. Official Johne’s disease test: An organism-detection test approved by the Administrator and conducted in a laboratory approved by the Administrator. The Administrator approves laboratories to conduct an official Johne’s disease test only after determining that the laboratory meets the check test proficiency requirements prescribed by NVSL. Approval continues as long as such check test proficiency requirements are met on an annual basis. Premises identification number: A unique number assigned by the State animal health official to a livestock production unit that is, in the judgment of the State animal health official and AVIC, epidemiologically distinct from other livestock production units. The premises identification number consists of the State’s two-letter postal abbreviation followed by the premises’ assigned number or code. Program: Voluntary Bovine Johne’s Disease Control Program. Screening test: A Johne’s disease test approved by the Administrator for use in the Voluntary Bovine Johne’s Disease Control Program and conducted in a laboratory validated through an approval process by NVSL. Screening tests are tools that have been developed to aid in determining the presence or absence of Mycobacterium avium ss paratuberculosis within a herd. Animals found positive to these tests should be considered suspect unless they show clinical
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signs of Johne’s disease (in which case they are considered positive) or they are confirmed positive or negative by an official Johne’s disease test. State: Any of the 50 States, the Commonwealth of Puerto Rico, the Commonwealth of the Northern Mariana Islands, the District of Columbia, and any territories and possessions of the United States. State animal health official: The State official who is responsible for the livestock and poultry disease control and eradication programs in a State. State Johne’s Disease Group: A group of interested persons organized by the State animal health official to assist in the oversight and coordination of the State’s Johne’s Program. Susceptible species: Domesticated and exotic ruminants, such as cattle, bison, sheep, goats, cervids, and camelids, that are capable of natural infection with Mycobacterium avium ss paratuberculosis. Test-negative herd: A herd that is enrolled in the Program, and meets the test-negative component requirements described in this document. Test-negative level: Level 1, 2, 3, or 4 with each increase indicating a lower probability of Johne’s disease in the herd. Test-positive herd: A herd that is enrolled in the Program and that meets the test-positive component requirements described in this document. Test-positive level: Level A, B, C, or D with Level A indicating zero or an extremely low prevalence and D indicating the highest prevalence of Johne’s disease in the herd. VS: Veterinary Services: The division of APHIS in charge of animal health activities within the United States. USDA: United States Department of Agriculture.
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Part II. Administration 1. Designated Johne’s Disease Coordinator (DJC) A. General Each State must have one person to act as its DJC. This person should be selected jointly by the State animal health official and the AVIC, and be approved by the VS regional Johne’s disease epidemiologist/regional director and the Johne’s disease staff of APHIS/VS/National Animal Health Programs. States have a 1-year grace period to allow the chosen DJC candidate to meet the education and training requirements. During this time period, the candidate is considered to be the acting DJC. B. Qualifications Each DJC candidate must: Be a State, Federal, or university veterinarian. Successfully complete a Johne’s disease (JD) epidemiology course that includes on-farm risk assessments and herd management plan development. Have at least 80 hours of experience in assessing risk, developing herd plans, and classifying JD test-positive animals and herds. C. Responsibilities The DJC has the responsibility to: Interpret laboratory test results and classify animals and herds based on the use of official and screening tests. Provide training for State personnel performing Program work. Provide training for certified veterinarians and develop a mechanism within the State to evaluate/monitor the involvement of the certified veterinarians. Review the risk assessments and herd management plans submitted by herd owners and certified veterinarians. Periodically audit the Program to determine if it is adequately controlling JD in the State. Assist animal health officials, herd owners, and the herd owner’s veterinarian with developing herd management plans as requested/needed. Participate in the Program activities as a member of the State Johne’s Disease Group.
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Provide a quarterly report to the VS regional Johne’s disease epidemiologist and the Johne’s staff of VS, National Animal Health Programs, on the progress of the Program. 2. State Johne’s Disease Group A. General A Johne’s disease group or an equivalent must be formed to assist the State in Program development, implementation, and review. A representative at the producer level, for either the beef or the dairy industry, is recommended as the chairperson for the group. The DJC must be a member. The group must meet at least once a year. B. Recommended members This group should include, but not be limited to: Dairy producers—purebred, commercial, and commodity groups Beef producers—purebred, commercial, and commodity groups University/extension faculty Animal health diagnostic laboratory personnel Regulatory veterinary medical officers—State, Federal, and/or field services Veterinary practitioners—beef and dairy 3. Johne’s Certified Veterinarians A. General States may elect to use the services of private practitioners in addition to State or Federal personnel to assist herd owners in conducting risk assessments and developing herd management plans. States using these veterinarians must determine that they meet the qualifications listed below. The DJC needs to develop a process to closely monitor the herd management plans developed by new Johne’s certified veterinarians. For example, the DJC may require the new certified veterinarian to develop the first one-to-five herd management plans in conjunction with an experienced animal health official. Johne’s certified veterinarians will be required to take a JD refresher course approved by the DJC at least once every 3 years. B. Qualifications. Johne’s certified veterinarians must be accredited veterinarians and demonstrate to the DJC that they have the knowledge needed to:
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Develop herd management plans Provide JD risk assessments Understand JD epidemiology, testing, and test interpretation Understand State and Federal Program requirements Collect and submit fecal, tissue, and blood samples for JD testing C. Responsibilities Johne’s certified veterinarians have the responsibility to: Provide risk assessments and develop herd management plans that will meet the approval of the DJC when requested by the herd owners Collect and submit samples according to the requirements set by the DJC
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Part III. Program Elements and Procedures 1. Education A. General The education element in each State serves as the entry level for producer participation in the State’s voluntary Program. The education element must provide producers with basic Mine’s disease information, management strategies for controlling and eliminating the disease, and information on the various aspects of the State’s Program. Education can take place through group workshops or through one-on-one sessions with the producer’s veterinarian. A record of participation should be kept. In the education element of the Program, producers should receive information concerning the following: B. Requirements Basic JD information—cause, clinical stages, transmission, etc. Management strategies for: Manure Colostrum and milk Replacements Infected animals Control and testing strategies: Testing Test interpretation The State Program 2. Management A. General Producers informed about Johne’s disease may wish to participate in the management element, an intermediate step in the Program. This recognizes producers for putting approved management practices and plans into place. At this stage, herd testing is an option available to the producer. The following components must be completed to the satisfaction of the DJC: B. Risk assessment Prior to developing an individual herd management plan, a risk assessment must be conducted in order to identify aspects of management likely to spread Mycobacterium avium ss paratuberculosis throughout the herd. A copy of the risk assessment must be submitted with the herd management plan to the DJC.
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recommended that they go directly to slaughter or rendering. A test-positive animal status may be appealed using the same appeal process described above for entry into the herd testing and classification element. If an animal is removed from the herd while screening test results are pending, a fecal culture should be collected, submitted, and held at the laboratory. This will allow the owner to appeal the herd level if the animal tests positive to a screening test. Optional—assessment levels. The State’s test-positive component may use assessment levels. Herds in a State program may achieve Level A, B, C, or D. Each level classifies a herd based on the known prevalence of Johne’s disease within the herd. The level achievement year should also be indicated. For example, a herd that completed Level B testing in 1998 and elects to remain at Level B would have a Level B 1998 status. The level achievement year should be noted because continued monitoring increases confidence that the herd prevalence is within that category. States that use assessment levels must follow the test-positive level requirements listed below. Level A—An annual herd test reveals no screening or official Johne’s test-positive animals. Level A can be maintained by achieving negative screening test results on 30 second or higher lactation animals every 10–14 months. Herds achieving Level A should be encouraged to enter the test-negative program at Level 1. Qualifying herds have: Negative test results on at least 30 randomly selected second or higher lactation animals (3 years old or older), Negative test results on the whole herd and on bulls over 2 years of age.
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Level B—An annual whole-herd test with the addition of bulls over 2 years of age reveals less than 5 percent of animals positive to a screening or official Johne’s disease test. Level C—An annual whole-herd test with the addition of bulls over 2 years of age reveals at least 5 percent, but not more than 15 percent, of animals positive to a screening or official Johne’s disease test. Level D—Herds should be classified as Level D if either of the following apply: test on at least 30 randomly selected second or higher lactation animals (3 years old or older) reveals one or more test-positive animals, OR a whole-herd test with the addition of bulls over 2 years of age reveals more than 15 percent of the animals positive to a screening or official Johne’s disease test. Renewal/Advancement A herd will remain in this classification for up to 14 months. For continuation, the herd owner must reapply with a copy of the test results, updated herd management plan, and an agreement to follow the test-positive component requirements. If the herd owner wishes to renew/advance but is waiting for confirmation of screening test results and therefore cannot meet the 14-month deadline, the herd owner can send the DJC a letter of intent to renew/advance. If the letter of intent is received by 30 days after the deadline, the DJC may allow the herd to retain its status for up to 5 months. Herds for which the necessary test results have not been supplied by the 5-month deadline must be placed in the management element. Owners of removed herds may reapply after the herds complete the required testing. D. Test-negative component (Herd Status) The test-negative component must include a herd management plan based on the requirements in the management element. The test-negative component includes a series of levels; owners may
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improve their herd status (achieve a higher level) by additional testing and biosecurity measures. Each higher level represents a greater probability that the herd is free from JD. However, this does not certify that a herd is free of JD. Herds in the test-negative component may remain at any given level by doing monitoring testing or may advance to a greater surveillance level with additional testing. Requirements for herds in the test-negative component include: Application The herd owner enrolling the herd must sign an agreement to abide by the requirements concerning minimum biosecurity and management established in the management element as well as the identification, testing, and herd addition requirements listed below. Herd additions Purchased heifers and bulls less than 2 years of age may be added to the herd provided that: The animal was purchased from a herd with a test-negative level that is equal to or higher than the herd it is entering, OR The purchased animal is tested in the next herd test after it reaches 3 years of age. The addition’s status will remain at its entry level until it has tested negative at that herd test. Purchased or replacement animals 2 years of age or older may be added to the herd provided that: For test-negative Level 1, 2, or 3 herds: The animal was purchased from a herd with a test-negative level that is equal to or higher than the herd it is entering, OR The animal has a screening test within 30 days prior to entering the test-negative level herd with negative results, and Fecal cultures are collected from each animal and submitted within 30 days of arrival, and
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The herd addition is tested on the next herd test. The addition’s status will remain at its entry level until it has tested negative at the next herd test. For test-negative Level 4 herds: The animal was purchased from a herd with a test-negative level that is equal to the herd it is entering, OR The herd of origin has a test-negative level of 2 or 3 and the purchased addition has a screening test with negative results within 30 days prior to entry into the program herd, and Fecal cultures have been collected from each animal added and submitted within 30 days of arrival, and The herd addition is tested on the next herd test. The addition’s status will remain at its entry level until it has tested negative at the next herd test. Heifers raised off the premises must be raised with the proper biosecurity measures in place and raised with animals at an equal or greater test-negative level. Test-negative program herds may use semen and embryos from other cattle herds provided that the semen used is processed according to Certified Semen Services standards and the embryos are processed according to International Embryo Transfer Society protocols. Embryo transfer recipient cows must meet herd addition requirements. Animal identification
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All animals must be individually identified using an official eartag. Any previous regulations listed in 9 CFR regarding animal identification for any other APHIS program still apply. Testing All samples must be collected by or under the supervision of an accredited veterinarian or a State or Federal animal health official. Vaccinated herds will be eligible for the test-negative component after vaccination has been discontinued. All testing must be done by an official Johne’s disease test until enough non-vaccinated natural additions qualify for serology testing. The number of non-vaccinated animals will be the sample size required for that size herd for a statistical subset for serology. All samples must be submitted to a laboratory approved by NVSL. Herd removal provisions—If an animal in a test-negative herd tests positive to a screening test or an official Johne’s disease test, or if the testing requirements are not followed, the herd must be removed from the test-negative component and placed in the test-positive component or in the management element (unless an appeal is pending). Appealing the status of a test-positive animal must be done using the same appeal process as for entry into herd classification and testing. Herd Advancement—Test negative Test negative herds may achieve Level 1, 2, 3, or 4. Each higher level represents a greater probability that the herd is free from JD. However, this does not certify that a herd is free of JD. The level achievement year should also be indicated. For example, a herd completing Level 2 testing in 1998 and electing to remain at Level 2 would have a Level 2 1998 status. All levels can be maintained by achieving negative screening test results on 30 second or higher lactation animals every 10–14 months. The level achievement year should be noted because continued monitoring increases confidence the herd is not infected. To advance from one level to the next, a statistical subset must be tested (Table IV–1), and the herd must meet the level requirements listed below for Standard Track or Fast Track test-negative component levels.
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Standard Track—The standard track is designed to allow entry into the Program with a minimal investment of funds and gradually increase the producer’s investment in the Program. The standard track will require at least 3 years and 4 tests to reach Level 4. Level 1—The herd owner has developed a herd management plan, and has agreed to abide by the requirements of the test-negative component, and the herd has had negative screening test results on 30 second or higher lactation animals. Level 2—Herds have met the requirements for Level 1, and have had negative screening tests on a statistical subset of second or higher lactation animals. Level 2 testing must be completed within 10–14 months of any Level 1 testing. Level 3—Herds have met the requirements for Level 2 and have had negative fecal culture results on a statistical subset of second and higher lactation herd members. Bulls 2 years of age and older must be included in this testing. The fecal culture must be collected within 10–14 months of any Level 2 testing. Level 4—Herds have met the requirements for Level 3 and have had a negative screening test on a statistical subset of second or higher lactation animals. Level 4 testing must be completed within 10–14 months of any Level 3 testing. Fast Track—The fast track allows producers to proceed to a higher level of confidence more quickly than the standard track, but requires greater financial investment at program entry. The fast track will allow herds to reach Level 4 in 2 years with three tests. Level 1—Skip this level if owner signs a declaration that no cows were seen or
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diagnosed with Johne’s disease in the past 5 years and has an approved herd plan in place. The State may require the declaration to be cosigned by the herd veterinarian. The signed declaration must include the following statements: I am fully aware of the management and disease history of the herd during the past 5 years. Johne’s disease is not known or suspected to have existed in the herd during the past 5 years or on the property during the past 12 months. No cattle have been introduced from known infected herds during the past 5 years. Level 2—Herds have met requirements for Level 1, and have had a negative screening test on a statistical subset of second or higher lactation animals. Level 2 testing must be completed within 10–14 months of any Level 1 testing. Level 3—Herds have met the requirements for Level 2 and have had negative fecal culture results on 30 second or higher lactation cows and all bulls 2 years or older. The fecal culture must be collected within 10–14 months of any Level 2 testing. Level 4—Herds have met the requirements for Level 3 and have had a negative screening test on a statistical subset of second or higher lactation animals. Level 4 testing must be completed within 10–14 months of any Level 3 testing. Renewal/Advancement A herd will remain at any level for up to 14 months. For continuation of this classification, the herd owner must reapply with a copy of negative test results, an updated herd management plan, and an agreement to follow the test-negative component requirements. If a herd owner wishes to renew/advance but is waiting for confirmation of screening test results and therefore cannot meet the 14-month deadline,
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the herd owner can send the DJC a letter of intent to renew/advance. If the letter of intent is received by 30 days after the deadline, the DJC may allow the herd to retain its status for up to 5 months. Herds for which the necessary test results have not been supplied by the extended 5-month deadline must be removed from the test-negative component. Herds removed from the test-negative component may reapply at the test-negative Level 1. Part IV. Laboratory Procedures 1. Approved Laboratories A. General All official Johne’s disease and screening tests used for the Program may be conducted in a private, university, State, or Federal laboratory that has been specifically approved for conducting JD testing. The State animal health official has the authority to decide if private laboratories may participate in the Program. States must have the authority to periodically audit the JD diagnostic laboratories participating in the Program. If a laboratory lies outside of the State, the State may rely on audits conducted by the animal health officials from the State in which the laboratory is located. B. Approval process for laboratories performing official Johne’s disease tests A laboratory seeking approval to perform official Johne’s disease tests must contact NVSL for a test kit of 25 samples. (A valid check test sample from NVSL will be determined by a consensus of at least 70 percent of the participating laboratories.) The laboratory must correctly identify 100 percent of the negative test samples. The laboratory must correctly identify 100 percent of the Too Numerous To Count (TNTC) test samples. The laboratory must correctly identify at least 70 percent of the test samples that were not classified as negative or TNTC. The laboratory must use the same procedure and materials during the check test as is used during routine testing. No retest is available within the same fiscal year. C. Approval process for laboratories performing screening tests (serology tests)
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A laboratory seeking approval to perform screening tests must contact the NVSL for a test kit of 25 samples. (A valid check sample will be determined by NVSL using available licensed ELISA kits.) The laboratory must correctly identify at least 90 percent of the serology check test samples. The laboratory must use the same procedure and materials during the check test as is used during routine testing. One retest is available if a laboratory fails the first time. 2. Approved Program Tests A. Official Johne’s disease tests Fecal/tissue culture—Culture is the standard for organism-based tests although culture methods are not currently standardized. Protocols for recommended methods can be obtained from NVSL upon request. Sensitivity is estimated at 40–10 percent; specificity is considered to be 99 percent if done correctly. DNA probe—DNA probes can detect the presence of Mycobacterium avium ss paratuberculosis without having to grow it. The test has the advantage that it takes a short time (less than 3 days) but has the disadvantages of higher cost and missing low shedders. Sensitivity is estimated at 40 percent; specificity is about 99.9 percent. Radiometric culture—Radiometric culture is a radioisotope-based method adapted from one used to isolate the bacteria that causes human tuberculosis. The method can detect low numbers of bacteria, and it is faster than standard fecal culture methods (7 weeks versus 16 weeks). The disadvantages are higher cost, the handling of radioisotopes, and the requirements for specialized instruments to read the culture vial. Sensitivity is approximately 40 percent; specificity is about 99 percent. Histology of tissue—No check test is available at this time. Microscopic identification of the characteristic pathological changes and of Mycobacterium avium ss. paratuberculosis organisms in tissue is a definitive test for JD. Tissue changes and bacteria can be observed in the intestinal lining and in nearby ileum, mesenteric, and ileocecal lymph nodes in infected animals. Sensitivity depends on the stage of disease and the number and type of specimens collected, but is typically considered to be greater
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than for other laboratory tests. Specificity is considered to be 100 percent based on defined criteria (e.g., granuloma with acid fast bacteria seen by a board-certified pathologist). B. Screening test USDA licensed Enzyme Linked Immunosorbent Assay (ELISA)—All animals found positive in ELISA tests should be considered suspect until confirmed using an official Johne’s disease test. ELISA tests are to be used as screening tools or for helping make management decisions. Sensitivity has been estimated at 25 percent for nonclinical cases and approximately 85 percent for clinical cases; specificity is between 98 and 99 percent.
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Table C-1. Herd Subset Sampling Number of Cattle in Herd (2nd or higher lactation) Number of Cattle to Sample (2nd or higher lactation) ELISA Fecal culture <300 Test all Test all 301–400 Test all 313 401–500 Test all 324 501–600 531 332 601–700 540 338 701–800 547 342 801–900 552 345 µ 901 580 360 Notes: In smaller herds, all cattle second or higher lactation must be tested. In herds with fewer than 30 second- and higher-lactation animals, first-lactation animals must also be tested. Sample numbers above have been based on the following assumptions: • The cattle to be tested are in second or higher lactation. • For these calculations, ELISA tests was assumed to have 25% sensitivity and fecal cultures was assumed to have 40% sensitivity (These were consensus estimates of the Herd Status Committee of the NJWG, USAHA for sub-clinically infected cows in first or higher lactation, and no changes were made for older populations sampled.) • For these calculations, 100% test specificity of the ELISA and fecal culture was assumed (given follow-up of all ELISA positives with fecal culture). • The confidence of detecting infection (at least 1 test-positive cow), if present at a true prevalence of 2%, is 95%. • Sampling without replacement.
Representative terms from entire chapter: