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Paratuberculosis
Johne's disease, or Johne's disease, is a chronic infection of the intestine of ruminants. The bacteria responsible thickens the intestinal wall, which no longer absorbs nutrients correctly: the animal loses weight even though it continues...
What is it?
Johne's disease, or Johne's disease, is a chronic infection of the intestine of ruminants. The bacteria responsible thickens the intestinal wall, which no longer absorbs nutrients correctly: the animal loses weight even though it continues to eat.
Its most confusing feature is its slowness. Calves become infected in their first weeks of life, but the disease does not appear until years later, in adult cows in full production.
When a first case becomes visible, the infection has already been present in the herd for a long time and other animals are contaminated without showing it. It is often said that one visible sick animal signals several invisible infected animals.
Key point
Disease listed by the World Organization for Animal Health and subject to surveillance programs in many countries. Any suspicion must be reported to the veterinarian, who will indicate the steps to follow.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Profuse, watery diarrhea, without blood or pain, which persists or returns despite usual treatments.
Progressive weight loss while the appetite remains preserved: it is the association which should alert you.
Decrease in milk production and animals that “no longer maintain” their lactation.
Dull and pitted coat, animal which loses its general condition without any other explanation.
Edema under the jaw in advanced stages, linked to loss of protein from the intestine.
Fatigue, weakness, then extreme emaciation.
Before this stage, infected animals appear normal for months or years while already shedding the bacteria in their dung.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease is caused by a mycobacterium, Mycobacterium avium subspecies paratuberculosis.
This bacteria is very resistant in the external environment: it survives for many months in dung, slurry, soil and stagnant water.
It settles in the wall of the intestine, where it causes chronic inflammation. The wall thickens and loses its ability to absorb nutrients and retain proteins.
Incubation is very long: contamination takes place during the first months of life, signs generally appear after two years, often around a period of stress such as calving.
Purchasing animals without knowing the status of the original herd.
Calving in an area soiled by dung, or birthing in collective housing.
Calf left for a long time with its mother on dirty bedding, or suckling on a soiled udder.
Distribution of mixed milk or colostrum from several cows to calves.
Spreading slurry on pastures for young animals.
Common drinking troughs, ponds and stagnant water points.
Large herds, with many introductions.
Transmission
Mainly by ingestion of contaminated dung: soiled udder, dirty litter, soiled water or food, soil of the calving area.
By colostrum and milk from an infected cow, especially when milk from several cows is mixed to feed calves.
From the mother to the calf during gestation, in some cases, particularly in cows at an advanced stage.
Newborn calves are by far the most receptive: the first weeks of life determine the risk for their entire life.
The introduction of an infected animal, without apparent signs, is the main route of entry into an uninfected herd.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian mentions the disease to an adult cow that is losing weight with persistent diarrhea, after ruling out internal parasites, deficiencies and other causes.
The diagnosis is confirmed in the laboratory: search for the bacteria in the dung by genetic analysis or culture, and search for antibodies in the blood or milk.
These analyzes detect sick or highly excretory animals well, but they miss a portion of animals infected at an early stage: a negative result does not guarantee that an animal is free.
At the herd level, screening is carried out over time, with repeated checks, and not through a one-off analysis.
When an animal is eliminated, an examination by the veterinarian makes it possible to confirm the diagnosis and assess the situation of the herd.
Treatment
There is no treatment to cure paratuberculosis. Antibiotics do not rid the animal of the bacteria.
An animal recognized as sick continues to massively excrete the bacteria and contaminates the calves in the herd: the decision to remove it is made with the veterinarian, without waiting until it is in a state of advanced thinness.
An affected animal must not be sold to another breeder or intended for breeding: it would carry the infection.
Its milk and colostrum should never be used to feed calves.
Supportive care may temporarily improve an animal's condition, but it does not change the outcome and delays a decision that is costly to the herd.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Everything revolves around calving and the first weeks of the calf's life.
Calving in a clean, abundantly mulched area, cleaned between each calving, never in an area soiled with dung.
Quickly separate the calf from its mother and house it in a clean place, away from adults and their droppings.
Give good quality colostrum from a single cow of known status, and prohibit mixtures of colostrum or milk from several cows.
Never give calves milk from a suspect cow.
Avoid young animals grazing on plots recently manured with slurry.
Control purchases: favor herds of known status, limit introductions, isolate and have incoming animals checked.
Gradually remove animals tested positive from the herd, starting with the most excretory, according to a plan established with the veterinarian.
Vaccines exist in certain countries but their use is restricted: they hinder the interpretation of tuberculosis screening tests. Their possible use is strictly a decision of the veterinary services.
Possible complications
Extreme weight loss leading to death or euthanasia.
Reduced production, infertility and early culling of animals in full career.
Increased susceptibility to other diseases in infected animals, even before signs appear.
Silent spread in the herd for years, with an economic cost much higher than the number of visible cases.
Restrictions on the sale of breeding animals.
When to see a veterinarian
An adult cow gradually loses weight even though it eats normally.
Watery diarrhea persists or keeps coming back despite treatment and deworming.
Edema appears under the jaw of a emaciated animal.
Many cows are losing condition without obvious cause in the herd.
You are considering purchasing animals and want to know the precautions to take.
You have already had a confirmed case: a control plan must be put in place, otherwise other cases will follow.
Prognosis
For the affected animal, the prognosis is hopeless: the condition deteriorates inexorably.
For the herd, however, the situation can be improved, provided you accept long-term work. Protecting calves at birth gives visible results after several years, while the protected generations replace the previous ones.
Farms that combine calving hygiene, colostrum management and regular screening manage to significantly reduce the disease.
Frequently asked questions
My cow is losing weight but eating well: is it necessarily paratuberculosis?
No, several diseases give this picture, starting with internal parasites and certain deficiencies. But the combination of weight loss and persistent diarrhea in an adult cow always warrants an examination and, often, a search for paratuberculosis.
Does milk from an infected cow pose a risk to humans?
A link with a human disease has been mentioned and studied, but it has not been demonstrated to date. The usual rules apply: consume pasteurized or boiled milk, and do not sell milk from a sick animal.
A single case in my herd, is it serious?
Yes, because a visible sick animal generally indicates several infected animals which are not yet showing anything. Now is the time to put in place measures around calving and a screening plan with your veterinarian.
Can I treat an affected animal with antibiotics?
No. No treatment cures this disease in cattle. The animal continues to excrete the bacteria and contaminates the calves: the decision to remove it is made with the veterinarian.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
EFSA — Autorité européenne de sécurité des aliments
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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