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Johne’s Disease Diagnostic Testing

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Johne’s Disease

Johne’s disease is a contagious, chronic, and usually fatal infection that primarily affects the small intestine of ruminants. It is found worldwide. Signs of Johne’s disease in cattle include weight loss and diarrhea with a normal appetite but are rarely evident until two or more years after infection. The causative bacteria are Mycobacterium avium subspecies paratuberculosis (MAP), and transmission is primarily fecal/oral to calves less than six months of age.

Based on the 2007 Dairy NAHMS study, about 68 percent of U.S. dairy herds have at least one cow that tests positive for Johne’s with herd prevalence approaching 100 percent in large dairy herds. In the typical herd, for every obvious case of Johne’s disease among dairy cattle on the farm, 15 to 25 other animals are likely infected. The clinical case represents only the “tip of the iceberg” of Johne’s infection. Infected animals often shed the organism through feces even before they show clinical signs, which allows for continued, unnoticeable infection of herd mates.

Sample Types

  • Milk
    • Fresh, frozen or preserved
    • Individual
  • Serum ( Fresh)
  • Fecal (Fresh)
    • Pooling available for AntelBio™️ STRATA-G™️ Johne’s PCR test minimum of 3 samples required for pooling strategy
  • Sheep and goats can only be tested with the blood ELISA

WHEN TO USE

  • Test milk or blood at dryoff or in early lactation (must be at least 7 days post freshening)
  • Test fecal samples at any stage after 2 years of age
  • Animals that are within 7 days of freshening have a high probability of giving false positive results when tested because of the presence of colostral antibodies.

Testing Strategies

  • Test milk or blood from recently fresh or soon to be dry cows with ELISA. Testing at these stages ensures every cow is screened annually and can be managed according to her results.
  • Verify positive animals with fecal PCR.
  • For low prevalence herds, skip ELISA screening and go straight to fecal PCR for more sensitive detection to find infected animals sooner.

Results interpretation

Reported as Positive, Negative or Suspect

ELISA

Positive

Antibodies against MAP were detected in the sample. Antibodies are proteins produced by the immune system in response to an exposure to Mycobacterium Avium Paratuberculosis.

Next Step Follow up with PCR
Negative

No BLV antibodies were present in the sample.

Next Step Recheck annually with ELISA
Suspect

MAP antibodies were detected in between the cutoff values and cannot be classified as positive or negative. This may occur due to early infection or low antibody concentration.

Next Step Retest with ELISA in 2-3 months or consider confirmatory testing with PCR.

PCR

Positive

MAP DNA was detected in the sample; this animal is shedding the bacteria and therefore may transmit infection.

Next Step If not removed from the herd, retest annually with PCR.
Negative

MAP DNA was not detected in the sample

Next Step Retest annually with PCR
Suspect

MAP DNA was detected in between the cutoff values and cannot be classified as positive or negative. This may occur due to early infection or low antibody concentration.

Next Step Retest in 2-3 months with PCR
CATTLE
Test Type Positive Negative Suspect
Milk ELISA >0.3 <0.2 0.2 – 0.3
Blood ELISA >0.55 <0.45 0.45 – 0.55
Fecal PCR <38.2 Undetected 38.2 – 40
GOATS & SHEEP
Test Type Positive Negative Suspect
Blood ELISA >0.55 <0.45 0.45 – 0.55

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Additional Information

Testing Supplies

FAQs

What is Johne’s disease and how does it spread?
Johne’s disease is a chronic intestinal infection in cattle, sheep, and goats caused by Mycobacterium avium subspecies paratuberculosis (MAP). The disease spreads primarily through the fecal-oral route, most often infecting young calves under six months of age. Infected animals can shed MAP bacteria in their manure long before showing symptoms, making early Johne’s disease testing critical for herd management.
What are the signs of Johne’s disease in dairy cows?
Typical Johne’s disease symptoms include chronic diarrhea, weight loss, and maintained appetite, though signs usually appear two or more years after infection. Because visible symptoms only represent the “tip of the iceberg,” many infected cows go unnoticed while spreading the bacteria to herd mates.
What types of tests are available for Johne’s disease?

CentralStar offers several Johne’s disease testing options:

  • Milk or Blood ELISA
    • Detects antibodies; ideal for annual herd screening at dry-off or early lactation.
  • Fecal PCR
    • Detects MAP DNA; identifies shedding animals.

Note: For sheep and goats, only blood ELISA is recommended.

When should Johne’s disease testing be done?
Milk or blood samples are best performed at dry-off or early lactation (at least 7 days post-freshening). Fecal PCR can be performed at any stage after 2 years of age. Annual testing leads to early detection and prevention of further herd contamination.
How do I interpret Johne’s test results?
  • ELISA Positive: MAP antibodies detected; confirm with PCR.
  • ELISA Negative: No antibodies detected; retest annually.
  • PCR Positive: MAP DNA detected; bacteria is being shed in the feces
  • PCR Negative: No MAP DNA detected; retest annually
  • Suspect Results: Retest in 2–3 months for confirmation.

Results are typically available within 5–10 days after sample receipt.

CentralStar’s laboratories provide sample analyses on milk, blood, fecal, and tissue samples for a variety of production, disease and health-related traits. More than 6 million samples are processed annually using state-of-the-art equipment and techniques including infrared spectroscopy, flow cytometry, ELISA, PCR, and more.

CentralStar laboratory services are intended solely for the detection of specific microorganisms or viruses in approved sample types. These services do not evaluate, certify, or guarantee the safety of milk for human consumption. It is recommended that interpretation of the results provided, and management decisions based on these results be done under the advisement of a veterinarian.