Risk of Maternal-neonatal Transmission
of Johne's Disease in Captive Exotic
Hoofed Stock

Johne's disease is a contagious bacterial disease that affects the intestinal tract of hoofed stock. The causative agent is Mycobacterium paratuberculosis. The clinical manifestation of infection is a chronic diarrhea and wasting disease. Infection ultimately results in death. Due to its insidious nature, the pathogen may become well established in a herd before disease is noticed.

Animals acquire the infection by being exposed to and ingesting the bacteria from another infected animal. Young animals are thought to be more susceptible to infection than are adults, but this has not been shown for exotic hoofed stock. Ingestion of the bacterium occurs when the newborn's environment is contaminated with manure from an infected adult animal, or by drinking milk from an infected animal. The milk may become contaminated from the environment (manure-stained teats) or, in the advanced stages of the infection, the bacterium is shed directly into the milk. This has been shown to occur in dairy cattle and is presumed to occur in other species as well.

Because there has been inadequate research on the management of Johne’s disease in exotic, captive animals, little is known about the effectiveness of removing nursing young. Studies demonstrating removal of young as an effective means of managing disease are in densely populated dairy herds, living in heavily contaminated birthing pens. These environments are very different than the field exhibits at the San Diego Zoo's Wild Animal Park, where animal environments are relatively clean and fecal matter is removed on a regular basis. For these reasons, staff has hypothesized that there is no increased risk of Mycobacterium paratuberculosis infection among offspring of test-positive dams in captive animal populations.

In order to test this hypothesis, an epidemiologic study is being conducted comparing risk for infection between offspring that nursed from an infected dam versus the remainder of the population. The management implications of this disease are important to the San Diego Zoo's collection and to zoological institutions throughout the world.