Ovine Ehrlichiosis (tick fever)
Ovine ehrlichiosis, more often called tick fever, is due to a bacteria which settles not in red blood cells but in white blood cells, that is to say in the cells responsible for defending the animal. The disease itself is rarely fatal. Its...
What is it?
Ovine ehrlichiosis, more often called tick fever, is due to a bacteria which settles not in red blood cells but in white blood cells, that is to say in the cells responsible for defending the animal.
The disease itself is rarely fatal. Its real danger lies elsewhere: by disarming the defenses for several weeks, it opens the door to other infections. Many problems attributed to something else start with it.
This explains a well-known sequence in flocks exposed to ticks: first a temporary fever, then, in the weeks that follow, lame lambs with abscesses, pneumonia, animals which do not respond as usual to treatments.
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:
High and sudden fever, which lasts several days with sometimes relapses in waves. This is often the only visible sign.
Dejection, animal which remains lying down, stops ruminating and eats less.
Rapid breathing during fever spikes.
Sudden drop in milk production in lactating females, sometimes more visible than the fever itself.
At the flock level, a general drop in feed intake and animals grazing less, without a single animal appearing really sick.
Abortion in pregnant ewes, particularly when fever occurs at the end of gestation.
In rams, swelling of the bursae and temporary infertility for several weeks: a ram affected during the fighting period can cause an entire breeding season to be missed.
Lambs which fail, no longer grow, and above all which become ill with something else in the weeks which follow.
In many animals, the infection goes unnoticed: only the consequence, a few weeks later, alerts the breeder.
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 bacteria is inoculated by the tick bite. It reaches the blood and enters a category of white blood cells, which it diverts for its own benefit.
These white blood cells being the first defenders of the body, their number drops and those that remain function poorly. The animal finds itself defenseless for several weeks, even after the fever has disappeared.
It is this window of vulnerability that explains most of the damage: the disease opens the way, another bacteria finishes the job.
A cured animal remains carrier for a long time and serves as a reservoir for ticks.
Animals introduced into a tick zone even though they have never been exposed to it have the most severe episodes; local animals often become immunized young.
Pastures in humid and wooded areas, undergrowth, forest edges, fresh meadows and brush: these are the environments where the responsible tick lives.
Spring and autumn, periods of peak tick activity.
Naive animals placed on an infested route for the first time: lambs in their first season, animals purchased elsewhere, herds moved during transhumance.
Lambing or control during tick season: the consequences on reproduction are then maximum.
Absence of a tick control program in a sector that is nevertheless at risk.
Association with other diseases transmitted by the same tick: several agents can be inoculated by a single bite.
Poor diet and internal parasitism, which make everything worse.
Transmission
By tick bite, exclusively in breeding conditions. There is no direct contagion between animals.
The tick in question needs humidity and vegetation that maintains freshness: woods, undergrowth, ferns, forest edges, damp meadows. The risk therefore follows geography as much as the season.
Cases concentrate in spring, with a second wave in autumn.
Sheep, goats and cattle can host the bacteria, as well as wild fauna: the cycle is maintained in an area even without a herd.
The bacteria can infect humans, but through the bite of the same tick and not through contact with a sick sheep.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian takes the temperature of several animals in the group, and not just the one that alerted: in this disease, fever is often the only sign and it passes quickly.
It is based on the context: recent grassing on a tick path, season, humid region, presence of ticks on animals.
A blood smear examined under a microscope can show the bacteria inside white blood cells during the febrile phase. After this stage, the examination becomes negative.
A blood test highlights the drop in white blood cells, which is very suggestive.
Specialized laboratory tests confirm the diagnosis and determine whether other agents transmitted by the same ticks are present.
When faced with abortions, the veterinarian systematically rules out other causes, which are numerous in sheep and some of which are dangerous for humans: this approach must never be abbreviated.
When lambs present with abscesses and lameness a few weeks after being put out to grass, the veterinarian readily traces this disease: the two problems are linked.
Treatment
A particular family of antibiotics, active on bacteria that live inside cells, helps bring down fever quickly. Antibiotics usually used for common herd infections do not work here.
The choice of product, route and duration is up to the veterinarian; no dose or rhythm should be decided alone.
The treatment makes the signs disappear but does not instantly restore the defenses: the animal remains fragile for several weeks. It is during this period that we must avoid other attacks, transport, overcrowding, dust in the sheepfold, sudden change of diet.
An anti-inflammatory can be prescribed by the veterinarian when the fever is very high and the animal is very depressed.
Affected animals especially need rest, shade, clean water and palatable food.
Monitoring the lambs in the group in the following weeks is an integral part of the treatment: this is where abscesses, lameness and pneumonia appear which will cause the real losses.
The waiting periods for meat and milk must be requested from the veterinarian and respected.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
The fight against ticks remains the only truly effective lever, and it protects at the same time against other agents inoculated by the same bite. The choice of product family, form and schedule is up to the veterinarian depending on the region and the season.
Avoid, when possible, putting naive animals on the most infested ranges at the time of peak tick activity, particularly lambs in their first season.
Shift lambing and control from the peak of ticks when flock management allows it: this is what limits abortions and loss of fertility in rams.
Clear brush and maintain the surroundings of sheep pens, containment corridors and paths where animals park.
Inspect animals by hand during the season and remove ticks without crushing them, using gloves.
Particularly monitor the lambs in the weeks following turning out to grass on a tick path: this is the time when complications appear.
Maintain a good diet and control internal parasites, so that animals get through the fragile period better.
Possible complications
Lamb tick fever: abscesses appear in the joints, muscles or spine due to the decline in defenses. It is the most classic and most expensive complication among young people.
Pneumonia and respiratory infections which appear in the following weeks.
Worsening of other diseases transmitted by ticks, inoculated by the same bite.
Abortions and weak lambs at birth.
Temporary infertility of rams, with a missed breeding season if the episode falls during the fight.
Fall in milk production which is not made up for in the current lactation.
Slow growth of lambs, rarely recovered.
Animals that respond poorly to usual treatments until their defenses have returned.
When to see a veterinarian
Many animals have a fever in the weeks following being put out to grass on a tick run.
The herd's milk production dropped suddenly without any other explanation.
Sheep abort: this is always a reason to call the veterinarian, several causes of abortion in sheep being dangerous for people.
A ram has swollen bursae or refuses to protrude during the wrestling period.
Lambs become lame, show swelling or are no longer able to stand up a few weeks after being released to pasture.
One flock eats significantly less and grazes for less time without any apparent cause.
The herd's usual treatments seem less effective than usual.
Transmission to humans
The responsible bacteria can infect humans, but contamination occurs through the bite of a tick, never through contact with a sick sheep, its meat or its milk.
The people exposed are those who frequent the same environments as the animals: shepherds, foresters, walkers in wet and wooded areas.
In humans, infection most often results in fever, headache and body aches in the days or weeks following a tick bite. Medical advice is necessary, reporting the bite: there is treatment.
The precautions are simple and protect against all diseases transmitted by ticks, some of which are serious: wear protective clothing and gloves when working among the herd, inspect your body after a day in the vegetation, remove ticks quickly without crushing or piercing them, and never crush them between your fingers.
Prognosis
The febrile episode itself almost always resolves, spontaneously or with treatment, within a few days.
The prognosis actually depends on the following: it is the period of fragility in the following weeks which causes the losses, especially in the lambs.
The consequences on reproduction, abortions and temporary infertility of rams, can cost an entire season even though no animal has died.
At the flock level, farms which control ticks and which delay lambing and control in relation to the peak of ticks do significantly better, year after year.
Frequently asked questions
My sheep had a fever then everything returned to normal: should we still take care of it?
Yes. The fever is only the first part of the story. For several weeks afterwards, the animals defend themselves poorly and easily catch something else. This is the time to monitor the lambs closely and avoid transport, overcrowding and sudden changes in feeding.
My ram has swollen bursae after the tick season, will he become fertile again?
It's possible: infertility linked to this disease is generally temporary and lasts several weeks. The problem is that it often falls in the middle of a period of struggle. Have the ram examined by the veterinarian, other causes of swelling of the bursae exist and are not benign.
Can I catch this disease from caring for my sheep?
Not through contact with animals, nor through their meat or milk. On the other hand, the tick that bites them can bite you too. Wear gloves and covering clothing, inspect yourself after a day in the vegetation and quickly remove any attached tick, without crushing it.
Does this disease exist everywhere in Tunisia?
No. The tick responsible needs humidity and dense vegetation: the risk is concentrated in humid and wooded areas of the North, not in dry regions. In arid areas, other diseases transmitted by other ticks are much more likely. The veterinarian in your area knows what is circulating in your home.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
ANSES — Agence nationale de sécurité sanitaire (France)
Content reviewed by the TunisieVet editorial team · Updated 10 September 2026
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