Questions and Answers

About Johne’s Disease in

Cattle

Q. What is Johne's disease, and what animals can

get it?

A. Johne's (pronounced "Yo-nees") disease is an

infectious bacterial disease of livestock that primarily

affects the intestinal tract. Johne’s disease should be

considered a herd problem as well as an individual

animal problem.

Cattle, sheep, and goats are most commonly

affected. The disease has been reported in several

species of wild ruminants, both captive and free ranging. In addition, a few reports of isolated cases in

nonruminants (including nonhuman primates) have

been reported, but none of the affected species are

believed to be sources for Johne’s disease in cattle.

Some studies have cultured the microbe from, or

detected its genetic components in, humans.

However, the significance of these findings as they

relate to any human disease has yet to be determined.

Q. What causes Johne’s disease?

A. Johne’s disease is caused by the bacterium

Mycobacterium avium subspecies paratuberculosis

and is often called by the acronymn MAP. MAP is a

distant relative of Mycobacterium bovis which causes

tuberculosis (TB) in humans and animals, but MAP

does not cause TB.

MAP bacteria grow and multiply inside the cells

of an animal’s immune system and are excreted in

the feces, and to a lesser extent in milk and saliva.

When the microbe is excreted, it can contaminate the

soil or water. Outside the host animal, the organism

multiplies poorly—if at all—but it can survive over a

year in the environment because of its resistance to

heat, cold, and drying. The primary cause of the

spread of Johne‘s disease is contact with the feces or

saliva of an infected animal.

Q. What are the signs of disease?

A. Because of the slow, progressive nature of the

infection, signs of Johne’s disease may not show up

until years after initial infection. When they finally do

occur, the signs are long-lasting diarrhea and weight

loss despite good appetite. Affected cattle do not

generally have a fever. Some infected animals

appear malnourished and weak; others just have

chronic diarrhea. Signs of Johne’s can easily be confused with those of several other diseases. In the

infected cow or heifer, noticeable signs commonly

start within a few weeks after a stressful event, like

calving.

Q. What causes the signs of disease?

A. The bacteria are taken up by specialized cells in

the part of the small intestine called the ileum, where

nutrients are absorbed from feed. As the body tries

to rid itself of these bacteria, the immune response

causes a thickening of the intestinal lining, preventing

it from functioning normally. This leads to poor

absorption of nutrients and eventual diarrhea. As a

result, although animals may be feeling and eating

well, they begin to lose weight gradually.

Q. Is Johne’s disease fatal?

A. Yes, once clinical signs of the disease appear, the

animal will not recover and will continue to deteriorate until it dies.

Q. Is there a cure for Johne’s disease?

A. No, a cure has not yet been found.

Q. How can I tell if my herd is infected?

A. Some animals may be infected, appear normal,

and be culled before they show any clinical signs.

Some owners may never realize that their herd is

infected. One hint in these herds could be that herd

production is going down or is not as high as it

should be, especially in 3- to 6-year-old cows. In

attempting to find the cause of low-herd production,

owners should test several ill-appearing animals for

Johne’s disease. In other herds, owners who see

one or more cows with diarrhea or weight loss should

consider Johne’s disease as a possible cause.

Environmental samples from cattle congregating

areas can also be cultured to determine if MAP, the

bacteria that causes Johne’s, is present on the premises.

Q. How can some cattle be infected with MAP, yet

not show signs?

A. Infectious diseases, including Johne’s disease,

typically pass through four stages. Stage I is initial

infection. The animal is infected but not showing

signs of disease. It may be shedding small numbers

of microbes into the environment that are not

detectable by diagnostic tests. In Stage II, the infection is progressing and the animal still does not show

any clinical signs. Nevertheless, the disease-causing
organism may be excreted in large numbers—enough

to infect other animals nearby. Infection is detectable

by fecal culture or DNA probe techniques but not

often by blood tests. In Stage III, a sick animal shows

the early signs of disease, and many types of diagnostic tests can detect the infection. Animals in Stage

IV show obvious clinical disease readily recognizable

by the trained observer and detectable by diagnostic

tests. It may take 2 or more years for Johne’s disease

to progress through all of these stages in an individual

animal.

A single herd affected by Johne’s disease, may

have animals in each of the four stages of disease.

For each animal showing obvious signs of Johne’s

disease (Stage IV), 5 to 15 times as many animals at

various stages of infection may be present but not

showing signs.

Q. What are common sources of MAP bacteria?

A. The most common source is feces, or manure.

While protected in fresh manure, the MAP organism

can remain alive in the environment for over a year,

depending on conditions. Ingestion of food tainted by

manure containing the microbe is the most common

way animals become infected.

MAP typically enters a herd via an infected, but

healthy-looking, animal in Stage I. As the disease

progresses in that animal, the frequency and number

of bacteria being excreted into the environment

increase. Every day, billions of Johne’s microbes may

be excreted from an animal in Stage III or IV of the

disease.

Another source of infection is milk from infected

dams. The likelihood of MAP being excreted in milk of

infected females increases as the disease progresses.

Studies suggest that 36 percent of cows with Johne’s

in Stage III and IV could have MAP in their colostrum.

In beef herds, where calves remain with their mothers

and nurse daily, the chance for transmission of the

infection through colostrum and milk is high. MAP

bacteria may be excreted directly through the mother's milk and they can be present on the outside of

teats and contaminated feces.

Prenatal exposure may be a source of infection for

calves. Becoming infected before birth is possible for

a fetus if its mother is in the late stages of Johne’s

disease. Studies have shown that, in dams with

Stage III or IV disease, from 8 to 40 percent of fetuses are infected while still in the womb. Risk for infection of the fetus is low from mothers in disease Stages

I and II, however.

Pond water and pastures contaminated with

infected feces are other potential sources of infection.

Q. Can humans get Johne’s disease?

A. Johne’s disease is not currently known to be transmissible to humans. However, there is a human disease called Crohn’s disease that resembles Johne’s

disease. One theory about the cause of Crohn’s disease is that, in genetically susceptible people, some

cases of Crohn’s disease may be incited by MAP.

Evidence for this theory is not conclusive, and uncertainty about potential risk to public health from this

organism persists. Crohn’s disease is not known to

occur more often in people exposed to the manure of

MAP-infected animals. MAP has been isolated from a

few humans with Crohn's disease, as have numerous

other bacteria and viruses.

Recent research from the U.S. Department of

Agriculture’s Agricultural Research Services indicates

that commercial pasteurization does inactivate the

MAP bacteria in milk. However, some researchers

still have concerns about MAP as a potential source

of human exposure in undercooked meat, unpasteurized milk products, and water.

Because of continued potential public-health concerns relating to Johne’s disease, animal-production

industries must give it more attention.

Q. Where can I obtain more information on

Johne’s disease?

A. For more information on Johne’s disease, contact

USDA–APHIS–VS

Center for Animal Health Programs

4700 River Road, Unit 46

Riverdale, MD 20737

Phone: (301) 734–4194

or visit the APHIS Web site at

<www.aphis.usda.gov>.

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