Using the HT-J test for detection or diagnosis of Johne's disease

Species:

Cattle, Sheep, Alpacas and Goats.

Specimen:

Faeces. Pooled or single samples. If pooled in laboratory, pooling fees apply.

Container:

Yellow top pot.

Pooling:

Bovine 5, Ovine 50, Caprine 50 and Alpaca 5. If pooled in the lab, a pooling fee applies.



KNOW YOUR DNA

Mycobacterium avium subspecies paratuberculosis (Map) is a slow growing mycobacterial agent which causes Johne’s disease (JD). Diagnosis of JD by culture is a long and complex procedure requiring multiple steps and tests to achieve a positive or negative result.

High Throughput Johne’s PCR (HT-J test) detects DNA consistent with the causative agent of JD (Map) . It is very specific to Map and results are usually obtained within 2-4 weeks. The HT-J test has been approved for herd tests in Australia and New Zealand by the Subcommittee on Animal Health Laboratory Standards (SCAHLS).

The benefits of running a HT-J test are: it is far quicker than faecal culture which can take months, it does not require the slaughter of animals for histology or tissue culture and it is more sensitive than the ELISA blood test.

Diagnosis of JD by faecal culture is a long and complex procedure requiring multiple steps and analyses to achieve a positive or negative result.

THERE ARE 4 STEPS:

1. Preparation
2. Liquid media culture
3. DNA testing of cultured organisms by PCR
4. Acid-fast staining using the Ziehl Neelsen stain
We no longer perform solid media culture.

HOW TO USE HT-J

The HT-J test is used to assess herd/flock infection status by using pooled faecal samples. The test can also be used on faeces sampled from individual animals, however, negative results are not definitive (at an individual animal level), as shedding can be absent or occur intermittently early in the course of infection. Other tests, such as ELISA and faecal culture are still required to confirm individual status.

Diagnosis of JD by HT-J means the herd/flock is likely to be infected. Further testing by culture may be required.

When negative HT-J test results are found across the whole herd/flock with sampling from high risk animals (e.g. animals greater than 2 years of age) then this indicates that the herd/flock is not shedding JD bacteria (Map). JD results should always be reviewed in the context of the history of disease on the property.

It is worth keeping in mind that although the HT-J test gives a quick result, if positive results are reported, it will take approximately 3 months for a confirmed diagnosis, if further JD testing by faecal culture is required.

THE FOUR STEP PROCESS TO CONFIRM JOHNE'S DISEASE IN HT-J POSITIVE/INCONCLUSIVE SAMPLES

         
Step Test
Procedure
Time
Frame
Alternate
Terminology
Purpose
1 Preparation ≈ 1 week Decontamination phase To prevent overgrowth by non Map organisms
2 Liquid media culture ≤ 12 weeks
  • Liquid M7H9C
To accelerate growth of Map
3 PCR ≈ 2 week
  • DNA testing
  • Strain typing
To detect DNA insertion sequences IS900 and IS1311 (in Map grown in liquid media) and determine strain type
4 ZN staining Done in same week as PCR
  • Acid fasting
To demonstrate acid fast staining of organisms grown in liquid media (other mycobacteria will also produce positive results)

Reference: Australian and New Zealand Standard Diagnostic Procedure, July 2015

PRICING (excluding GST)

         
Request Pooled 4 week TAT Pooled 2 week TAT Single 4 week TAT Single 2 week TAT
High Throughput Johne’s
(HT-J) PCR
(1-30 samples)
$90.00 $164.40 $85.00 $142.40

To order the HT-J test please send required samples on ice packs in eskies to Gribbles Veterinary Pathology along with your submission form (available to download at gribblesvets.com.au/veterinarians/ordering-a-test). Please write High Throughput Johne’s PCR in testing instructions.

Samples need to arrive in the laboratory within 48 hours of collection. Please keep this in mind when scheduling sample collection.

Paratuberculosis (Johne’s disease) is a notifiable disease. Refer to www.agriculture.gov.au/pests-diseases-weeds/animal/notifiable for reporting obligations in your state or territory.