F406
Johnes Disease
(Mycobacterium paratuberculosis)

Introduction: Johnes disease, pronounced YO-knees (or paratuberculosis), is a chronic bacterial disease of the intestinal tract in ruminants (sheep, goats, cattle, deer, antelope, and llamas). This disease is difficult to identify in its early stages and is usually fatal. Johnes disease occurs in a large variety of animals and is widely distributed across all regions of the United States.

Causative Agent: Johnes disease is caused by bacteria called Mycobacterium paratuberculosis. This organism is highly resistant to the infected animal’s immune defenses and can survive in the environment for over a year. Infected animals harbor the organism for years before they develop clinical signs or test positive for the disease.

Sources of Infection: The disease typically enters a flock/herd when an infected, but healthy looking animal is brought into a healthy flock/herd. The infection then spreads to non-infected animals when they ingest fecal material from another infected animal. Once outside the animal, the bacteria are quite hardy and may live for months in water, feed, and feces. In the later stages of infection, the bacteria are found in the milk of infected animals. Young animals can become infected by drinking milk from infected ewes/does. Research also suggests that an infected mother can pass the disease to the fetus during pregnancy. Animals younger than 6 months old are the most vulnerable to infection. Certain animals in the flock or herd may not be infected, others may be infected but not shed the bacteria, while some may be infected and shed the bacteria to other animals. Different animals may move from one category to another throughout their life.

Clinical Signs: Clinical signs rarely appear until the animals are 1-2 years of age or older. Signs usually first appear following lambing/kidding, a severe stress, or under conditions of poor management. Severe weight loss that progresses to complete emaciation is the most common sign. Unlike Johnes infections in cattle where diarrhea is extremely common, infected sheep and goats rarely have diarrhea (soft, non-formed pellets). The skin and hair may be dry, flaky, and rough. Generally, only one or two animals in a flock or herd have clinical signs. Infected animals frequently eat well and look bright, but appear unthrifty. They generally do not have a fever. This disease develops so slowly that by the time the owner becomes concerned there may be a widespread problem within the flock/herd.

Diagnosis: An excellent way of identifying an animal with Johnes disease is by running a fecal culture or fecal smear. This test detects the bacteria that cause the infection. At least six fecal pellets should be collected from each suspect animal and sent to the diagnostic laboratory as soon after collection as possible. If the transport to the laboratory will take an extended amount of time, the fecal material should be frozen. Infected animals that are not shedding the organism in the feces will not test positive on this type of test.