Department of Pathobiology, Johne’s Testing Center, School of Veterinary Medicine, University of Wisconsin, Madison, WI, USA
Johne’s disease (paratuberculosis), a fatal and contagious gastrointestinal disease of ruminants, has been diagnosed by the Johne’s Testing Center by radiometric culture of the causative agent, Mycobacterium paratuberculosis at 5 of 49 zoos over the past 2 years.
Control of this slowly developing disease can be troublesome in a zoological park. The biology of this disease makes surveillance difficult as clinical and immunologic signs can be subtle and appear late in the disease process. Infection usually occurs in the first few months of life, but markers for diagnosis (e.g., cytokine and antibody production, fecal shedding of the organism) may show up months to years later. The majority of infected animals shed organisms but appear clinically normal. The full impact of herd infection can be masked both by the years that can pass before clinically affected animals are detected and by the dispersion of animals (and the infection) to other collections through breeding exchanges and sale.
There are a number of methods available for surveillance and detection of animals with Johne’s disease. Application of a number of testing techniques can greatly improve the effectiveness of a Johne’s disease control program. Reliable animal identification systems and accurate record keeping are critical to managing this, as with any, disease control program.
Detection of infected animals or herds may rely on some or all of the following techniques:
1. Clinical assessment by keepers, curators, and veterinarians.
2. Necropsy screens of collection and feral animals.
3. Serologic detection (new species-specific and multi-species ELISAs are in development).
4. Bacteriologic culture (biopsy/necropsy tissue, feces, environmental samples).
5. Genetic probe.
Once clinical signs compatible with Johne’s disease are noted in an animal, detection of an immunologic response to infection or detection of M. paratuberculosis itself is necessary to confirm the clinical diagnosis. Clinically affected animals are the most likely to have produced antibody in response to infection and to regularly be shedding the organism. The choice of detection method is influenced by available resources (time as well as money), animal species and Johne’s disease prevalence in the exhibit. For most situations, bacteriologic culture to isolate the organism from fecal samples is the best choice to confirm clinical suspicions. AGID or ELISA testing may be useful for faster verification of the diagnosis in animals with clinical signs consistent with Johne’s disease.
Should the clinical diagnosis be confirmed, further steps are necessary since Johne’s disease is a herd problem as well as an individual animal problem. Once a diagnosis has been made in a single animal, carefully examine herd-mates, offspring, and the environment for signs and pathways of infection. Colostrum/milk used for hand-rearing infants, exposure of young stock to adult manure, exposure to contaminated water in exhibits and fecal contamination of feed bunks are a few of the routes in which the disease may be transmitted to other animals. Consider annual fecal culture screening of all adult animals in the exhibit. Infected animals should be euthanatized or at least isolated and their offspring should be evaluated as well.
Johne’s disease should always be on the list of differential diagnoses generated for a thin animal. The cost of missing the diagnosis in a herd of exotic hoofstock can be so severe that the expense of ruling it out must be accepted. In exhibits where there is any possibility of Johne’s disease (based on clinical assessment, exposure or test results), early detection of infectious animals is critical. Regular (annual) screening of adult animals over a period of years is necessary to reveal and eliminate a herd infection. For optimal fecal culture screens, three samples should be collected some days or weeks apart. This protocol will improve the likelihood of obtaining samples containing organisms from animals shedding M. paratuberculosis intermittently. Picking up samples from a clean stall or pen floor from animals held for a short time or from the ground in the exhibit itself is acceptable for animals that cannot easily be penned and handled.
Control of disease transmission in a herd or exhibit following detection of an infected animal may include:
1. Exhibit sanitation: removal and composting of feces, elimination of standing water, tuberculocidal disinfectant for all tools, boots, etc.
2. Keeper and veterinary staff awareness of clinical signs.
3. Necropsy screens (primary tissues of interest include the distal gastrointestinal tract and associated lymph nodes).
4. Milk and colostrum from Johne’s disease-free sources for hand-reared neonates.
5. Annual herd testing, testing of animals with compatible clinical signs and culling or isolation of test positive animals.
In many zoos, three negative fecal cultures collected some weeks apart are required prior to accepting animals into quarantine at the new site. While in quarantine, an additional fecal culture is recommended, preferably on a sample collected immediately after arrival at the new facility, as it is thought that an animal is more likely to shed the organism when stressed. Testing requirements for export are as specified by the receiving country.
“Children’s Zoo” Animals
Many facilities seasonally introduce new ruminants to the more permanent residents of the Children’s Zoo collection. The source herd for these animals should be assessed for Johne’s disease. An optimal arrangement is to contract with the source herd owners and specify the infectious disease testing protocol for the entire source herd to improve the likelihood that individual animals brought to the zoo are not infected. These source herds may then also serve as sources of M. paratuberculosis-free milk/colostrum.
It is expected that the U.S. Department of Agriculture will define paratuberculosis as a “program disease” in the near future. This means that Congress will allocate funds to stimulate control and/or monitoring of Johne’s disease. While focused on agricultural animals, zoological collections may also be affected by new regulations. Regulatory topics of particular concern are mandatory slaughter of animals with positive fecal culture results and an amendment of CFR 80 to halt interstate movement of fecal culture-positive animals.
An association between M. paratuberculosis and Crohn’s disease, a human inflammatory bowel disease, is still being explored. The public perception of a zoonotic risk and actual risk are not always in synchrony: deflecting both the perception of and a potentially real zoonotic risk is recommended for the zoo community. This can be done by establishing and documenting control programs for Johne’s disease.
Members of AAZV and other individuals with expertise in mycobacterial infections currently are investigating development of guidelines for diagnosis and control of Johne’s disease in zoological collections. These guidelines are expected to support uniform interpretation of test data, pre-shipment test requirements and other aspects of paratuberculosis control of benefit to the zoo community at large.