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Ovine paratuberculosis
Johne's disease, also called Johne's disease, is a chronic infection of the intestine caused by a very resistant bacteria, a cousin of tuberculosis but which is not tuberculosis. The bacteria gradually thickens the wall of the intestine, wh...
What is it?
Johne's disease, also called Johne's disease, is a chronic infection of the intestine caused by a very resistant bacteria, a cousin of tuberculosis but which is not tuberculosis.
The bacteria gradually thickens the wall of the intestine, which loses its ability to absorb food. The animal eats normally but no longer gets anything from its ration: it loses weight slowly, over months, until it dies of exhaustion.
Two characteristics make it a particularly feared disease in herds. First, it is incurable: no treatment cures an affected animal. Then, it is silent for years: lambs become contaminated in their very first weeks of life and only show signs in adulthood, after having already sowed the bacteria everywhere.
Key point
Johne's disease is not visible: when the first animal loses weight, the bacteria has already been circulating in the herd for years. A thin animal with a preserved appetite, which does not respond to any dewormer, warrants a veterinary visit for the entire herd, not just for itself.
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:
Slow and steady weight loss, over several months, while the animal continues to eat and the ration is correct. This is the major sign, the one that should raise the alarm.
Dull, brittle wool, which comes off in patches; the animal remains dirty and poorly finished despite care.
Reduced milk production, lighter lambs, ewes that never recover after lactation.
Fatigue, animal which stays behind the herd and often lies down.
Pale mucous membranes in advanced stages, and soft swelling under the jaw due to protein leaking from the intestine.
Soft, poorly molded droppings, or diarrhea that comes and goes. In sheep, this sign is inconsistent and often arrives late: its absence never rules out the disease.
In the end, the animal remains lying down, never gets up again and dies despite all care.
At the herd level, we especially notice a series of thin animals that do not respond to anything: no deworming, no mineral supplements, no change in ration.
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 very resistant mycobacterium, which survives for months, sometimes more than a year, in damp soil, manure, water from puddles and ponds.
Infected animals shed huge amounts of bacteria in their droppings, often long before they appear ill.
Contamination occurs mainly in the first weeks of life: the lamb swallows the bacteria by sucking on a soiled udder, by licking dirty litter, or by drinking contaminated water.
The bacteria can also pass into the colostrum and milk of an infected female, and sometimes cross the placenta in severely affected females.
Once entered, the bacteria settles in the wall of the intestine and remains there for years without causing anything. The signs most often only appear after two years, sometimes much later, and often during stress: giving birth, lactation, transport, scarcity, drought.
Purchase of animals without knowing the health situation of the herd of origin: fairs, markets, over-the-counter transactions.
Lambing in an overcrowded sheepfold, on dirty and damp bedding, with soiled udders.
Mixing lambs with adults and their droppings from the first days of life.
Distribution of raw mixed milk from several females: a single infected female then contaminates numerous lambs.
Watering in ponds, puddles and streams receiving runoff from smoked plots.
Spreading of fresh manure on plots then grazed by young people.
Mixed breeding combining sheep, goats and cattle on the same areas.
Moist and poor soils, which favor the survival of the bacteria.
Habit of keeping and caring for thin animals for a long time instead of culling them.
Transmission
The main route is the ingestion of droppings, directly or through litter, water, soiled fodder and dirty udders.
Colostrum and milk from an infected female also transmit the bacteria to her lamb.
Young people are by far the most receptive; adults become infected much more difficult.
The introduction of a purchased animal is the main gateway to a disease-free herd. This animal may appear in perfect health and have already been eliminating the bacteria for months: no examination upon purchase guarantees that it is healthy.
Equipment, boots, vehicles and manure spreading carry the bacteria from one farm to another.
Buildings and plots remain contaminated long after the sick animals have left.
Sheep, goats and cattle share the same bacteria: the mixture of species maintains circulation.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Faced with a thin animal with a preserved appetite, the veterinarian begins by eliminating the other causes of chronic weight loss in sheep: digestive parasitism, poor teeth, deficiencies, chronic lung diseases, internal abscesses, tumors. Several of these causes can be treated, hence the importance of not concluding too quickly.
A very telling field reference: an animal which continues to lose weight despite correctly administered dewormer and sufficient nutrition must suggest paratuberculosis. Repeating deworming without results is a warning sign, not a solution.
The tests available are the search for bacteria in droppings and the search for antibodies in the blood. They detect sick animals well, but let a large proportion of infected animals pass which do not yet show signs. A negative result therefore never guarantees that an animal is healthy: this is the major limitation of screening.
For this reason, screening is carried out at the herd level and is repeated over time, rather than focusing on an isolated animal.
The necropsy of an affected animal is very informative: thickened and wrinkled intestine and large lymph nodes are characteristic. It is often the examination that finally makes the diagnosis in a herd. Do not let an animal die of weight loss disappear without talking to the veterinarian.
Slaughterhouse returns can also alert you to an established infection.
Treatment
There is no treatment that cures paratuberculosis. Antibiotics do not cure it: the bacteria is protected within the wall of the intestine itself.
A diagnosed animal must be removed from the herd without delay, along with its descendants, because it massively contaminates the environment and especially the young.
Dietary support and supplements may temporarily improve an animal's appearance, but do not change the outcome. Above all, they delay the decision and prolong the contamination of the herd: this is the most common trap.
The course of action is decided with the veterinarian and concerns the flock, not the individual: identify affected animals, cull, protect newborns, review lambing management and purchasing policy.
Eliminate affected animals according to current regulations and do not leave their corpses or waste accessible to other animals.
The decision to slaughter an animal still in condition is made with the veterinarian, taking into account the rules applicable to the slaughterhouse.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention is entirely based on two ideas: not letting the bacteria enter, and protecting newborns.
When purchasing: favor animals from herds whose health situation is known, avoid purchasing over the counter from strangers, and systematically quarantine. A thin animal should never be purchased, regardless of its price.
Lamb in a clean and dry place, on abundant and renewed litter, with cleaned udders.
Separate lambs from adults and their droppings as soon as possible, and do not graze them on the most soiled areas.
Avoid raw formula milk of unknown origin for artificial breastfeeding.
Cull the offspring of females recognized as affected: there is a high chance of them already being infected.
Water from the tank rather than from ponds and puddles, and avoid grazing the young on freshly manured plots.
Immediately cull any animal that loses weight without explanation, instead of trying to get it back for months.
Set up, with the veterinarian, a regular screening plan in affected herds: control takes place over several years, not over one season.
Vaccination
Vaccines against paratuberculosis exist and are used in sheep and goats in certain countries. They do not eliminate the infection: they reduce the number of animals which develop the disease and the quantity of bacteria eliminated in the environment.
Their use is regulated and sometimes subject to authorization, in particular because vaccination interferes with the interpretation of tuberculosis screening tests. It also often leaves a lasting local reaction at the injection site.
Availability and conditions of use vary depending on the country: the question should be asked to the veterinarian, who will indicate what is possible locally and if this is of interest in your situation.
In all cases, vaccination does not replace lambing hygiene, nor caution when purchasing, nor the culling of affected animals: it complements rigorous breeding management, never in its place.
Possible complications
Weight loss to the point of exhaustion and death of the animal, despite all care.
Decrease in fertility, births and milk production in affected herds.
Lighter and more fragile lambs, born to infected mothers.
Increased susceptibility to other diseases in malnourished animals.
Long-lasting contamination of buildings and plots, which affects several years after the disappearance of the sick animals.
Slow, diffuse and difficult to quantify economic loss, often wrongly attributed to parasitism or food.
Difficulty selling breeding stock and cleaning up the herd once the disease has set in.
When to see a veterinarian
An animal slowly loses weight even though it eats normally.
Several animals in the herd lose weight without explanation over the months.
An animal does not react to dewormer, supplements, or change of ration.
A soft swelling appears under the jaw in a emaciated animal.
Intermittent diarrhea sets in in an animal that has been losing weight for a long time.
A thin animal dies: ask for an autopsy before putting it to death, it is often this which gives the diagnosis.
You are considering buying breeding stock: talk to the veterinarian before purchasing, not after.
Prognosis
The prognosis of an affected animal is clear: there is no cure, the progression is towards weight loss and then death.
The prognosis of the herd depends entirely on the precocity and firmness of the reaction. A farm where we identify early, where we cull without hesitation and where we protect the lambs can significantly reduce the number of cases over the years.
A farm where thin animals are kept and cared for, where lambing is done in the mud and where people continue to buy without precaution sees the disease take a lasting hold and weigh on all results.
Sanitation is a long-term job, which is measured in years and is worked out with the veterinarian.
Frequently asked questions
My sheep is losing weight but he eats well, and I have dewormed several times without result. What is happening?
This is exactly the picture that should make you think of paratuberculosis. Several other causes exist, such as poor teeth or chronic lung disease, and some are treatable. But repeating the dewormer does not help: have the animal examined, and talk to the veterinarian about the entire herd.
Can we treat an affected animal?
No. There is no treatment that cures this disease, and antibiotics do nothing. Keeping an affected animal by feeding it better only delays the maturity while massively contaminating the litter, the plots and especially the lambs.
Is this dangerous for my family?
Transmission to humans has not been demonstrated. A link with human intestinal disease has been mentioned and is the subject of work, without established proof to date. As a simple precaution, it is reasonable not to consume raw milk from an affected herd and to wash your hands after handling the animals.
How can I avoid bringing her into my herd?
By buying as little as possible, and never blindly: find out about the herd of origin, refuse any thin animal and quarantine. Then, protect the lambs, which become contaminated in their first weeks: clean and dry lambing, cleaned udders, rapid separation from adult droppings.
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 11 August 2026
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