Because we co-raise kids we test annually for CAE prior to the doe's freshening.  We no longer test for CL as testing is inaccurate, and there are too many false negatives and false positives with this testing.  CL can only be identified by testing the pus from an abscess.  All abscesses are tested if they occur.  We have not had any positive cases of CL in our herd.  Additionally, we no longer test for Johnes disease through the Elisa method as it is not an accurate testing strategy.  We will now do pooled fecal testing yearly on goats over 2 years old since shedding of MAP (the bacteria that causes Johnes)  is unlikely in young animals. You may request a copy of our herd testing results.

In our opinion, testing non-symptomatic animals through ELISA gives a false sense of security that a small herd is negative for Johnes.  Johnes can be in any herd, even herds who "test negative or claim they are a closed, clean herd".   According to Cornell University College of Veterinary Medicine (https://www.vet.cornell.edu/animal-health-diagnostic-center/programs/nyschap/modules-documents/johnes-testing-strategies)  The below statements were taken directly from their website.  I highly suggest reading the full source "Johne's Testing Strategies" as you will be more informed about the reliability of Johne's testing in individual animals and herds.

• Johne’s tests are not perfect in describing individuals’ infection status. One serology or culture test in known infected animals can in average terms be expected to miss over 60% of them; more false negative than true positive results are expected to occur (assume Se range of 25-40%). For Johne’s ELISA serology, testing known uninfected animals is expected to find 2% of them as false positive (Sp in range of 98%, 98% of uninfected cattle test truly negative).

• Johne's tests in individual animals have relatively low ability to detect earlier stages of infection, even in mature cattle. This is due to the relatively low sensitivity (25%-40% range) of serology and fecal tests. Thus, there is a 60-75% chance that an infected animal will test negative on a single test.

• The utility of an individual Johne’s test in immature animals is even more limited. Less than 5%-10% of infected animals may be detected because most are in stages of infection that are too early to detect.

• Before purchasing animals:

• Know the risk within the home herd for Johne’s and other diseases of importance.

• Consider the risk from the possible source.

• Decide on what is an acceptable level of risk for the several other possible diseases one might bring in: BVD; Strep ag, Staph, Mycoplasma mastitis; Salmonella; Neospora; Digital dermatitis; Cryptosporidia, etc.

• If Johne's is a priority, consider Johne’s serology of the source herd - at least 30 mature animals as is recommended in the National Voluntary Johne’s Herd Status Program.

• Johne's tests in individual animals have relatively low ability to detect earlier stages of infection, even in mature cattle. This is due to the relatively low sensitivity (25%-40% range) of serology and fecal tests. Thus, there is a 60-75% chance that an infected animal will test negative on a single test.

To read more go to https://www.vet.cornell.edu/animal-health-diagnostic-center/programs/nyschap/modules-documents/johnes-testing-strategies

 

This was a facebook post from Laurie Hunt when she received a false positive ELISA test in her herd.  Permission granted to copy, paste, and share.

 

Here is my correspondence with Dr. Michael Collins from Johnes. org

He is likely the most educated person in this country on the matter.

Hi Laurie,

Many people test for Johne’s disease (JD) using a blood test, called ELISA. What they fail to understand is that the ELISA is only a rapid, low-cost screening test and cannot definitively diagnose JD. Only by using a fecal PCR test to detect MAP in a fecal sample can a diagnosis of JD be confirmed.

A single negative fecal PCR indicates that the goat is not shedding MAP in its feces at the time of sampling. It significantly raises the probability the goat is not MAP-infected. However, due to the chronic nature of this bacterial infection, repeat testing at one-year intervals is advisable. After 3 negative fecal PCR tests done a year apart by qualified labs you can be 99+% sure the goat is not MAP-infected.

It is very possible that the positive blood test was a false-positive. This is especially true of the goats are in contact with backyard poultry. I posted a news item about this which you can find on this page of my website: https://johnes.org/news/page/3/

I recommend that breeders not use the ELISA but only use the fecal PCR for their annual herd test. To control costs, I further recommend that goat breeders use laboratories that are USDA-approved to pool samples (5 goat fecals per pool).

For owners of commercial, the decision about JD testing requires consideration of more things.

To learn more about JD in goats I encourage you to view the 20 minute video on my site:

https://johnes.org/presentations-and-mini-lectures/

Presentations and Mini-lectures

These short mini-lectures are designed to make Johne’s information readily accessible to everyone. Sometimes thing are better explained in words than in documents. Check back as more presentations will be added in early 2019. MAP is a Zoonotic Pathogen Michael T. Collins, DVM, PhD, DACVM, Professor, University of Wisconsin-Madison, School of Veterinary Medicine. This short 20…

johnes.org

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This link takes you to a UDSA page for a list of approved labs by test type. Scroll down to the one labeled “Johne’s disease – pooling methods”.

https://www.aphis.usda.gov/.../sa.../ct_approved_labs

If this reply does not address all of your concerns, I am happy to talk later today (3-5 pm Central time). Let me know and I will call you.

Mike

Johne's Information Center

Michael T. Collins, DVM, PhD, DACVM

Professor Emeritus

School of Veterinary Medicine

University of Wisconsin-Madison

I talked with him over the phone after this at great lengths. Here are some other things that I now know

1) Johnes is largely contracted by baby goats and very rarely adults. They did a test where they put contaminated feces into a water bucket and let adults drink and the animals that came up positive where next to none. They don't know why.

2) goats will usually carry the disease for 2 or 3 years before they start shedding it. It's a silent disease...So they can be in your herd for a long while with negative test results.

3) a fecal PCR is 100% accurate. You can't have a false positive. The fecal can test negative when they aren't shedding the MAP bacteria yet however

4) at first... they can shed intermittently. When they start wasting, they will shed all the time and then they will die

5) taking intestinal samples to test the ileum and peyer's patches doesn't work on young goats because the damage won't be detected that early. So you can use that to check a deceased goat, but a fecal is still going to be better for herd security.

6) you are more likely to have a false negative than a false positive.

We should all be testing by fecal PCR every year. Once you are clean for 3 years and you aren't bringing in new animals... your clean. That's it. Blood work from WADDL or anyone else doesn't mean you are clean. It's a worthless test. 

 

*The only caveat I would add to this is that outside sources can still bring in disease, since dear are a rumanant I would guess that they could also bring in disease including Johnes so even if you are a closed herd and tested negative 3 years in a row it is still not unforseeable that something else does not bring in disease.  Keep testing!