JOHNE'S DISEASE FACTS
Johne's Disease targets all ruminates. Johne's Disease (JD) is a worldwide problem of domestic and wild animals and is also a potential public health concern. A chronic granulomatous inflammatory intestinal disease, JD results from infection with Mycobacterium avium subspecies paratuberculosis (Map). A German veterinarian first described the disease in a dairy cow in 1865. His name is used as the common name for the disease; it is sometimes referred to as paratuberculosis.
JD is most often seen in ruminants, hoofed animals that chew their cud and have a 3-4 chambered stomach. Some of the more common ruminants are cattle, sheep, goats, deer, antelope and bison. JD has been reported in all these animals but is now recognized to be a serious economic and animal health problem in domesticated ruminants, primarily dairy and beef cattle, sheep and goats. The growing recognition of Map infection in wildlife species is also of great concern since it may limit opportunities to control or eradicate JD from domesticated animals.
JD occurs worldwide. According to the Johne's Information Center, it is estimated that 7.8% of the beef herds and 30% to 70% of the dairy herds in the U.S. are infected with Map. Infection rates in cattle in other countries are generally similar or larger. The disease has been reported in sheep, goats, elk, deer, bison, llamas and wild ruminants in zoos, but accurate estimates of the number of infected animals are not available. A recent report on JD from the National Research Council (NAS) of the US National Academies of Sciences concluded that JD is a significant animal-health problem whose study and control deserves high priority from the USDA and other national and state agencies. It was recognized that the problems associated with JD stem from:
- Difficulties in diagnosis because of an unusually long incubation period and a lack of specific and sensitive diagnostic tests for detecting early infections.
- Vaccines have been ineffective in treating JD.
- An absence of general awareness of the disease and its true economic and animal-health consequences.
Although first described over a century ago, JD is now recognized to be a serious economic and animal health problem throughout the world.
- Affects small intestine in ruminants
- Highest at risk animals are young calves or pre-born.
- Bacterium can survive in contaminated soil for over 1 year.
- Spread in herds can occur by fecal contamination, colostrum, milk, and transplacental.
- Calves can become infected by suckling on “dirty” teat
- For every one “clinical stage” in a herd there are 15-20 silently infected plus additional 6-8 carriers.
Stage I: Silent, subclinical, non-detectable infection, typically this stage occurs in all calves, heifers, and young stock less than two years of age and many adult animals exposed to small doses of disease-causing organism. Infected animals at this early stage are rarely detected with currently available diagnostic tests, including fecal culture or serologic tests (ELISA). This stage progresses slowly over many months or years to stage II.
Stage II: Subclinical infection, typically this stage occurs in older heifers or adults. Animals at this stage appear healthy but are shedding adequate numbers of MAP organisms in their manure to be detected on fecal culture. Blood tests will detect some, but not all animals at this stage. Blood test (ELISA) positive animals should be confirmed positive by fecal culture.
Stage III: Clinical JD, any animal with advanced infection, the onset which is often associated with a period of stress, such as recent calving. Cattle at this stage have intermittent, watery pea-soup manure. Animals lose weight and gradually drop in milk production but continue to have a good appetite. Some animals appear to recover but often relapse in the next stress period. Most of these animals are shedding billions of organisms and are positive on culture. Most are positive on serologic tests (ELISA & AGID). Clinical signs often last several weeks to months before the animals are sent to slaughter in a thin, emaciated condition. In the final and terminal aspects of stage III of the fatal disease, animals become emaciated with fluid diarrhea and develop “bottle jaw”. The carcass may not pass meat inspection for human consumption in the later phases of stage III.
There are multiple industry drivers that take place in the JD market. These encompass both government, economic, and health:
- Reduction in milk production up 25%+.
- Increased costs to feed infected animals to produce.
- Reduction of quality wool in the sheep industry.
- Paratuberculosis in cows causes the largest economic damages for dairy farms worldwide.
- High culling rate which increases costs.
- JD affects trade and hinders exports.
- Increased government regulations.
- Increased veterinarian costs.
- Studies are discovering a link between JD and Crohn’s disease.