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Sheep yersiniosis
Yersiniosis is an infection of the intestine caused by bacteria of the Yersinia genus. It mainly affects young growing sheep, weaned and antenais lambs, and results in diarrhea that resists usual treatments. Its particularity, which explain...
What is it?
Yersiniosis is an infection of the intestine caused by bacteria of the Yersinia genus. It mainly affects young growing sheep, weaned and antenais lambs, and results in diarrhea that resists usual treatments.
Its particularity, which explains almost everything, is that these bacteria like the cold: they multiply at low temperatures, in water, in soggy soil and in wet fodder. Cases therefore occur in winter and early spring, in cold, rainy and windy weather, while most digestive problems in sheep tend to strike in the hot season.
The disease typically breaks out after stress: weaning, transport, change of diet, undernutrition, prolonged bad weather without shelter.
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:
Watery diarrhea, often greenish or grayish, sometimes with mucus and traces of blood.
Soiled hindquarters, wool stuck to tail and thighs.
Rapid weight loss in animals which until then were growing: it is this sudden decline which strikes the breeder.
Despondency, animals which remain lying behind the lot, and which no longer follow.
Refusal to eat and dehydration.
Fever in some animals, often moderate and short-lived.
Pale mucous membranes when diarrhea persists.
A few deaths, generally among the most affected or weakest animals.
In a batch, several animals are affected over a few days to a few weeks, while the others remain apparently healthy.
Detail that often puts us on the trail: animals do not improve after correctly administered deworming.
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 responsible bacteria live in the external environment and in the digestive tract of many animals, particularly wild birds, rodents and cats, which eliminate them without becoming ill.
They multiply at low temperatures: cold water, soggy soil, wet fodder and damp litter constitute excellent reservoirs.
Animals become contaminated by swallowing these bacteria with water, soiled grass or fodder that has fallen to the ground and been trampled.
The presence of the bacteria is not enough: there is almost always a triggering factor that lowers the defenses, weaning, transport, undernutrition, prolonged cold and humidity.
Once installed, it inflames the wall of the intestine, which lets water leak and no longer absorbs it: hence diarrhea and rapid weight loss.
Combination with digestive worms and coccidiosis is common, which further confuses the picture.
Weaned and growing lambs: these are by far the most affected.
Cold and humid period, end of winter and beginning of spring, prolonged episodes of rain and wind.
Weaning, transport, sorting, batch or building change, especially when these events are grouped together in the same week.
Sudden change in diet, insufficient ration, period of scarcity.
Lack of shelter from wind and rain on the plots.
Drinking from puddles, streams and dirty water troughs.
Fodder distributed on soggy and trampled ground, instead of a rack.
Food stocks accessible to birds and rodents.
Animals already weakened by digestive worms or coccidiosis: problems often accumulate in the same animals.
Transmission
Transmission occurs through the mouth, from a contaminated environment: water, wet ground, fodder fallen on the ground, damp litter.
Wild birds and rodents contaminate food stocks and water troughs: these are important relay points, often neglected.
Sick animals eliminate the bacteria in their droppings and in turn contaminate the lot and the plot.
Cold and humidity promote the survival and even multiplication of bacteria in the environment, unlike most germs: a rainy winter is a risky season.
There is no contagion through simple contact between clean and dry animals: it is the environment that causes the disease to circulate.
Human beings can be contaminated by the same routes: unsafe water, soiled food, dirty hands after contact with sick animals or their bedding.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Faced with diarrhea in weaned lambs, the veterinarian cannot conclude anything by eye: coccidiosis, digestive strongylosis, salmonellosis and yersiniosis give similar symptoms and are treated differently.
He therefore takes samples: analysis of droppings to look for parasites and coccidia, and culturing to look for bacteria. This culture requires special conditions, so it is necessary to specify to the laboratory that yersiniosis is suspected, otherwise it may go unnoticed.
The autopsy of a dead animal is particularly useful: lesions of the intestine and lymph nodes quickly guide the diagnosis. Don't make a dead lamb disappear in the middle of a bout of diarrhea.
The veterinarian looks for the triggering element: date of weaning, change of ration, weather of the previous weeks, presence of shelter, quality of water and fodder.
A valuable guide for the breeder: a batch of lambs which does not improve after a correctly administered dewormer should seek something else, and not receive a second dewormer.
Treatment
Call the veterinarian as soon as several animals in a group have diarrhea: this is when you can still protect the others.
The treatment combines antibiotics, chosen by the veterinarian and if possible guided by a laboratory analysis, and rehydration, which remains the measure that saves the most affected animals.
Do not give an antibiotic on your own initiative and do not reuse a leftover bottle: the choice of product depends on the germ, and poorly conducted treatment maintains resistance without curing the animal.
A dewormer given alone does not solve anything if it is yersiniosis. It can nevertheless be justified at the same time when the analyzes also show parasites, which is common in these animals.
Remove sick animals from the lot, shelter them from wind and rain, on dry bedding, with clean water and good quality fodder.
Immediately improve the conditions for the entire lot: shelter, food, clean water, fodder distributed in the rack and not on the ground. Without this correction, cases continue despite treatment.
Respect the withdrawal times for meat and milk prescribed products.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Spread out the stress factors: do not wean, transport, sort and change the ration in the same week.
Take care of the weaning period, which is the most risky: gradual food transition, sufficient ration, homogeneous and stable batches.
Providing shelter from the wind and rain on the plots during the cold season: this is often the measure that is missing.
Distribute the fodder to the rack or trough, never on wet and trampled ground.
Guarantee clean water: clean drinking troughs, prevent drinking from puddles and streams.
Protect food stocks from birds and rodents, and control rodents in buildings.
Simultaneously control digestive worms and coccidiosis, which weaken the same animals at the same age.
Monitor batches of weaned lambs closely during cold and wet periods, and have them analyzed at the first instance rather than waiting.
Wash your hands after handling sick animals or their bedding: the bacteria also affects humans.
Possible complications
Death from dehydration in the most affected animals, especially when treatment has been delayed.
Sustainable growth delay, which penalizes the entire lot until the sale and does not completely catch up.
Anemia and general weakening after prolonged diarrhea.
Permanently soiled hindquarters, which attracts flies as soon as the heat returns and prepares the ground for myiasis.
Increased susceptibility to other diseases in weakened animals.
Episodes that repeat each winter as long as shelter, water and weaning management are not corrected.
Possible contamination of the human environment, particularly children.
When to see a veterinarian
Several weaned lambs from the same batch have diarrhea during a cold, wet period.
Animals lose weight quickly even though they were growing.
Diarrhea contains mucus or traces of blood.
An animal is dehydrated, slaughtered, or no longer gets up: consult the same day.
Animals do not improve after deworming: do not re-deworm, have them analyzed.
Lambs die during an episode of diarrhea: keep the body cool for the veterinarian.
A person on the farm presents fever, diarrhea and stomach pain during the episode: they must consult a doctor and report contact with the animals.
Transmission to humans
The bacteria responsible for yersiniosis in sheep can also infect humans. Contamination occurs through unsafe water, contaminated food, and hands put in the mouth after contact with sick animals, their droppings or their litter.
In humans, the infection causes fever, diarrhea and especially right-sided abdominal pain which can resemble an attack of appendicitis, particularly in children and adolescents. Joint pain may appear in the weeks that follow. Medical advice is necessary, and it is useful to report contact with sick animals to the doctor.
These bacteria multiply in the cold, including in foods kept in the refrigerator: refrigeration therefore does not protect, only correct cooking does.
The precautions are simple: gloves for handling sick animals and soiled bedding, washing hands with soap after each contact and before eating, clothing and boots reserved for breeding, and young children kept away from affected premises.
Do not drink untreated water on the farm and do not consume raw milk from sick or treated animals.
Prognosis
Animals treated early, rehydrated and returned to shelter most often recover well.
Those who have lost a lot of weight have stunted growth which weighs on the lot until sale.
Some losses are common among the most affected animals, especially when treatment has been delayed by dewormers given blindly: it is the time lost which costs the most.
At the scale of the lot, progress depends as much on correcting conditions as on treatment: shelter from wind and rain, sufficient food and clean water weigh as much as medicine.
Frequently asked questions
My weaned lambs have diarrhea in the middle of winter, even though I have dewormed them. For what ?
Because they might not be worms. Yersiniosis strikes lambs weaned in cold, wet weather, and no wormer does anything about it. A flock that does not improve after a properly administered dewormer should be analyzed, not dewormed a second time.
How to distinguish it from coccidiosis?
We cannot distinguish them by eye: same age, same season, same diarrhea, and they often overlap. Only an analysis of droppings, supplemented by culturing, allows us to make a decision. Tell the veterinarian that you suspect yersiniosis, because its investigation requires special laboratory conditions.
Why does this disease appear in winter and not in summer?
Because the bacteria multiplies in the cold, in water, in soggy soil and wet fodder. This is the opposite of most germs. The cold and the rain also weaken animals already stressed by weaning: the two effects are cumulative.
Can I catch it myself?
Yes, it's a zoonosis. In humans, it causes fever, diarrhea and right-sided stomach pain that sometimes resembles appendicitis, especially in children. Wear gloves when caring for sick animals, wash your hands with soap, and seek medical attention when reporting contact with the herd.
References
EFSA — Autorité européenne de sécurité des aliments
CDC — Centers for Disease Control and Prevention
Content reviewed by the TunisieVet editorial team · Updated 11 August 2026
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