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April 2010 Issue

What's the Best Test?

An Affordable and Successful Way to Test for Johne's Disease

by Michael T. Collins, DVM, PhD
Professor, University of Wisconsin-Madison School of Veterinary Medicine

How do diagnostic tests fit into a Johne's disease control program? Experts agree that it's prohibitively expensive to do a fecal culture or IS900 polymerase chain reaction (PCR) test on every cow. It doesn't make sense to spend more money to control a problem than the problem costs in the first place. However, for a chronic and contagious infectious disease, like Johne's disease, it's vital to look long term (e.g., a 10-year time frame) at the costs and benefits of control programs, including diagnostic testing. Failure to recognize the infection in a herd and take positive actions to control it today will most likely mean a much higher herd infection rate and significantly higher cost to the herd in the future.

A low infection rate in a herd (<5% ELISA-positive) is not nearly as costly as a high infection rate (>10% ELISA-positive), which can and has put dairy herds out of business. Therefore, the best advice to commercial dairy producers is:

1. Confirm whether your herd is infected—if yes, then...
2. Start an effective control program!

What we've learned from a careful cost-benefit analysis is that lower-cost tests like the IDEXX* Mycobacterium paratuberculosis Antibody Test Kit, used with blood or milk samples, are more cost-effective for commercial dairy herds than are higher-cost, more-sensitive tests, such as fecal culture and PCR. We also now know that it is not necessary to cull each and every test-positive cow from a herd. A more cost-effective approach is to cull only the cows with a high test result (strong positives) and to keep, but label and carefully manage, cows with low- to medium-level test results.

Three Farms Demonstrate Successful Johne's Disease Management

Dairy farmers are finding success in reducing the incidence of Johne's disease by using the IDEXX Mycobacterium paratuberculosis (M. pt.) Antibody Test Kit as a disease management tool and by implementing production management changes.

Read the reports of three successful dairy farms featured in "Healthy Cows for a Healthy Industry," a special insert in Hoard's Dairyman, reprinted with permission.¹

Blaser Farm

When the Blasers first started the Johne's management program, more than 50% of their cull cows were positive for Johne's disease. Now that number is 10% or less.

Verhasselt Farm

The first enzyme-linked immunosorbent assay (ELISA) test showed that the Verhasselts had to discard colostrum from 549 cows, almost 40% of their herd.

Feider Farm

Cow number 4 tested strong-positive for Johne's, even though her condition looked healthy. Not all Johne's-positive cows are thin and sickly.

Paratuberculosis: A Global Problem

Paratuberculosis is chronic enteritis of ruminants and other animals, caused by Mycobacterium avium subsp. paratuberculosis (MAP). It is categorized by the World Organization for Animal Health as a list B disease that is of serious economic or public health importance. First recognised in cattle, then in sheep, and later in goats, paratuberculosis is found among domestic and wild ruminants.

In the U.S. dairy industry alone, the annual loss of productivity from Johne's disease is estimated to be as high as $250 million.¹ Studies show that cows testing positive for the disease produce less milk and have reduced pregnancy rates, while the milk produced has lower fat and protein content and higher somatic cell scores. MAP can cost producers up to $250 per animal in infected herds.²

Disease Is Easily Transmitted

MAP has a broad geographic distribution. Johne's disease has been reported on every continent, in virtually every country that has animal agriculture and laboratory diagnostic capability.

Infected animals shed MAP bacteria in feces, milk and colostrum. Bacteria can be transmitted in semen. Unborn animals can be infected in utero.

Subclinical carriers remain infectious.

Clinical Signs Are Tip of the Iceberg

Animals are usually infected with Johne's disease before 6 months of age, but clinical signs often don't appear until the animal is 1–2 years of age, and incubation can last for years.

Signs include:

• Diarrhea that is initially intermittent, but becoming progressively worse until it is constant
• Malabsorption syndrome and muscular wasting
• A drop in milk production

Not every infected animal shows clinical signs.

Several Diagnostic Methods Are Available

For individual animals, a tentative clinical diagnosis must be confirmed by laboratory tests, especially if the animal is from a farm in which the disease has not previously been diagnosed.

Diagnosis of MAP-infected animals can be performed by detecting MAP bacteria using PCR, traditional or liquid-culture methods, or by detecting antibodies against MAP.

Include ELISA Testing Among Protective Measures

Protective measures are essential for the health of livestock and can help to protect farmer income. These measures include testing animals and controlling the movement of people, animals and vehicles.

• Use an ELISA to test animals regularly for MAP, and cull positive animals based on the ELISA S/P ratios, separating positive from negative animals.
• Use an ELISA to test every new animal before bringing it into the herd.
• Ensure that animals are born in clean facilities; ensure timely removal of calves from cows.
• If feeding colostrum manually to newborns, obtain colostrum from MAP-negative animals; make sure colostrum is collected hygienically; avoid pooling colostrum.
• Make sure that milk, feed and water supplied to young livestock are clean (free of manure contamination); ideally only pasteurized milk products, such as milk replacer, should be fed to neonates until weaning.
• Require visitors to clean their shoes before entering the farm.
• Require that equipment be cleaned before it enters the property, or that vehicles and other equipment be parked away from livestock.

Announcing USDA Approval of the New IDEXX* Mycobacterium paratuberculosis Antibody Test Kit, with Milk Claim

IDEXX Production Animal Services is pleased to announce the release of the new IDEXX Mycobacterium paratuberculosis Antibody Test Kit for U.S. and Canadian customers. The new kit detects antibodies for Mycobacterium avium subsp. paratuberculosis (MAP) in serum, plasma and milk samples.

Designed to help dairy and cattle producers manage the impact of MAP (also known as Johne's disease), this USDA-licensed ELISA offers the following benefits:

• Sensitivity and specificity superior to other tests on the market. Excellent test performance minimizes the need for retesting and ensures quick turnaround time.
• Approval for use with milk samples (as well as serum and plasma samples). U.S. and Canadian dairy producers can save money by requesting MAP testing on the milk samples they routinely collect to evaluate milk quality. No extra sample collection is required.
• Laboratory efficiency and accuracy. Laboratories benefit from proven technology, the flexibility of having a single kit that can be run with milk, serum or plasma samples, and the simple and rapid test protocol.

The new kit's milk claim will reduce the cost of testing for U.S. and Canadian dairy farmers, while having a positive impact on dairy productivity.

Diagnostic Specificity (Milk) 99.8%

†Presumed-negative animals, based on herd history

Key points:

• 633 of 634 samples correctly identified as negative
• Specificity = 99.8% (95% CI, 99.0%–100%)

Diagnostic Sensitivity (Milk) 74.2%†

Key points:

• 124 U.S. and European fecal-culture-positive samples
• The new IDEXX Mycobacterium paratuberculosis Antibody Test Kit correctly identified 92 of 124 samples as positive.
• Sensitivity = 74.2%† (95% CI, 65.8%–81.1%)

†Expected sensitivity in typical field populations is lower.

Overall Performance

Performance Compared to Competitor ELISA

The IDEXX Mycobacterium paratuberculosis Antibody Test Kit demonstrated better sensitivity than Competitor A, when used with milk samples.

†Sample status was determined by fecal culture or samples were from herds with known positive status. For positive samples, suspect results were treated as negative (not detected); for negative samples, suspect results were treated as positive (detected).

‡Sample status was determined by fecal culture or samples were from herds with known positive status.

The IDEXX Mycobacterium paratuberculosis Antibody Test Kit Offers Benefits to Laboratories, Veterinarians and Producers Worldwide

Multiple sample types:

• Milk and plasma claims, in addition to a serum claim, using proven Insitut Pourquier* technology (small ruminant claim available outside the U.S.)

Accurate results:

• Excellent specificity and sensitivity; out-performs the sensitivity of other ELISAs used with milk
• Consistent lot-to-lot performance and within-lot performance

Rapid turnaround time:

• Simple, rapid test protocol with results in less than 2 hours
• Familiar ELISA format—no retraining needed
• Suitable for manual, semiautomated or fully automated work flows
• Compatible with xChek* software for fast result interpretation

Dependable supplier:

• Kits produced in an ISO-certified facility
• Reliable and steady supply, with support you can trust

Ordering Information

In U.S./Canada:

• IDEXX Mycobacterium paratuberculosis Antibody Test Kit
• Reference number: 99-14444
• For use with bovine serum, plasma and milk

Outside U.S./Canada:

• Pourquier Paratuberculosis Screening ELISA
• Reference number: P07130
• For use with bovine serum, plasma and milk, and with serum and plasma of sheep and goats

Compare the New IDEXX* Mycobacterium paratuberculosis Antibody Test Kit to the HerdChek* M. pt. Ab ELISA

The differences between the new IDEXX Mycobacterium paratuberculosis (M. pt.) Antibody Test Kit and its predecessor, the HerdChek M. pt. Ab ELISA, are outlined below.

Kit Components

Kit Protocols

The easy-to-learn protocol is similar to the protocol for the HerdChek M. pt Ab ELISA, but the kit can be used with milk and plasma, as well as with serum.

Results Interpretation

The test calculates the ratio of the sample value to the positive control value (S/P) and includes a suspect zone. Color development in the test indicates a positive result.

Events Around the World

• Chapecó, Brazil—April 6–8
  XI Simpósio Brasil Sul de Avicultura
  cleovet@nucleovet.com.br
• Thaba Nchu, South Africa—April 7–9
  Livestock Health and Production Group Congress
  http://www.vetlink.co.za
• Melbourne, Australia—April 12–14
  2010 Foot and Mouth Disease (FMD) International Symposium and Workshop
  http://www.fmd2010.com.au/
• Vancouver, British Columbia, Canada—April 18–21
  59th Western Poultry Disease Conference and ACPV Workshop
  http://www.cevs.ucdavis.edu/confreg/index.cfm?confid=455
• Utrecht, The Netherlands—April 20–22
  VIV Europe 2010
  http://www.viveurope.nl/en/Bezoeker.aspx
• Athens, Georgia, USA—April 26–30
  AMEVEA Programa XII Seminario Internacional de Patología y Producción Aviar
  http://www.amevea.org/
• Florianópolis, Brazil—May 11–13
  AveSui 2010 América Latina
  http://www.avesui.com/AveSui2010/WebSite/Home/Default.aspx
• Berlin, Germany—May 27–29
  8th International Symposium on Turkey Diseases
  http://www.vetmed.fu-berlin.de/einrichtungen/kliniken/we15/termine/Turkey_Diseases_2010/index.html

Please Join IDEXX in Supporting the World Food Program

Last December, IDEXX started a partnership with the United Nations World Food Program (WFP). WFP is the largest humanitarian agency fighting hunger worldwide, both in emergency situations, such as Haiti, and through longer-term efforts to help communities build their capabilities for a safe and sufficient water and food supply.

"The Production Animal Services, Water and Dairy businesses all contribute to food production efficiency and food/beverage safety worldwide. We believe a partnership with WFP in general, and assistance for those affected by the Haiti disaster in particular, reinforce our values," said William Goodspeed, Corporate Vice President of Production Animal Services, Water and Dairy.

In Haiti, WFP is coordinating logistics for the United Nations, the International Red Cross and other organizations on the ground. As of February 2, WFP reached around 850,000 earthquake victims. The agency has also reestablished basic logistics and telecommunications infrastructure in Haiti, but much more support is needed.

To find out what you can do to help, or to learn more about WFP, please visit the WFP Web site.

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