Johne’s disease

By CS McConnel, Veterinary Medicine Extension

Recently a case presented to WADDL that served as a reminder of the challenges related to managing Johne’s disease (MAP, Mycobacterium avium subspecies. paratuberculosis) within goat herds. This case involved a 5-year-old doe (we’ll call her Jane) that was purchased with intake serology performed via ELISA (enzyme-linked immunosorbent assay). This test identifies antibodies produced by a MAP-infected animal. At that time Jane was deemed negative via the ELISA. A year later she was ELISA test negative again as part of annual surveillance within her new herd. Jane was sold to another herd a year later without having been tested and soon thereafter became debilitated and died. At that time her feces was tested for MAP via PCR (polymerase chain reaction) and she was determined to have died of Johne’s disease.

Although additional inquiries suggested that Jane had been somewhat of a “poor doer” prior to being sold the second time, her history of negative serologic results from ELISA belied her infection with MAP. Unfortunately, this is fairly common. According to the go-to for Johne’s information (, ELISAs “are designed for rapid, low-cost screening of large numbers of animals. ELISAs are less sensitive than MAP-detection assays (PCR and culture), typically being positive in roughly 30%-50% of the animals that MAP-detection assays will identify as MAP-infected. This is generally because antibody production occurs later in the course of a MAP infection, months or even years after an infected animal has been passing MAP bacteria in its feces.” The good news is that ELISAs are >99% specific which means that there is a <1% chance that a positive ELISA is a false-positive. The bad news is that surveillance using ELISAs clearly can miss infected animals and deliver a false sense of security.

It is worth noting that unfortunately fecal PCR has limitations as well. Infected animals that are shedding MAP do not necessarily shed consistently. That means that any given fecal sample has the potential to miss the bacteria’s presence. Conversely, it is possible for MAP to be detected in feces as a result of bacterial pass-through as opposed to true infection. In other words, if a herd with infected animals is housed together with the potential for fecal-oral contamination, it is possible for the MAP bacteria to be ingested and pass through the GI tract without establishing an infection—those bacteria can be identified within the feces and falsely indicate infection in that individual.

Overall, a producer should consider impacts of Johne’s disease through the lens of both current infection prevalence and/or disease transmission. As such, the following approaches have been laid out to provide some guidance in managing the diagnosis of Johne’s disease for goat owners. These recommendations and much more can be found in the Frequently Asked Questions at Johne’s Information Center.

Question: Is MAP present in my herd?

Recommendation: Use targeted testing (ELISA or fecal PCR) of oldest or thinnest goats (10% or more of the herd).

Question: How many of my goats are infected?

Recommendation: A good estimate can be made by blood testing (ELISA) all goats after their second kidding or older.

Question: What test should I use to control MAP in my infected herd?

Recommendation: For commercial herds, blood testing (ELISA) on all goats after their second kidding or older is economical. See the Control section for further information.

Question: What test should I use to eradicate Johne’s disease in my herd?

Recommendation: Breeders must work to eradicate MAP. Pooled fecal culture is an economic way to eliminate the infection in the herd.

Question: Does this skinny goat have Johne’s disease?

Recommendation: After ruling our parasites, fecal PCR is best. Even better is necropsy (autopsy) where a pathologist examines the tissues and a microbiologist attempts to detect MAP in tissues by PCR.

Question: What test do I need to sell and transport this goat?

Recommendation: This is determined by the agency managing the shipment or the receiving owner. If I were advising the buyer, I would recommend a test on source herd (all adults or at least 30 head) by fecal PCR (pooling acceptable). Buying young animals from such a herd is reasonable safe. If the herd owner can show you 3 years of whole-herd negative test results that would be even better.