Reindeer hypodermosis (varron)
Reindeer hypodermosis, also called varron disease, is a parasitic infestation of the skin caused by the larvae of a fly called Hypoderma tarandi. This fly lays its eggs on the reindeer's coat during the summer. The larvae that emerge then...
What is it?
Reindeer hypodermosis, also called varron disease, is a parasitic infestation of the skin caused by the larvae of a fly called Hypoderma tarandi.
This fly lays its eggs on the reindeer's coat during the summer. The larvae that emerge then migrate through the body of the animal before settling under the skin of the back, where they form characteristic nodules.
It is a very common disease among reindeer and caribou in arctic and subarctic regions. It does not concern reindeer raised outside these geographical areas since the responsible fly is absent there.
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:
During the summer, reindeer attacked by adult flies show intense agitation: they run, shake their heads and try to escape, which can disrupt their eating and rest.
Several months later, in winter and spring, hard, tender nodules appear under the skin on the back. Each nodule contains a larva and has a small breathing hole visible on its surface.
The skin around the nodules may become irritated, crusty, or break through, sometimes oozing some fluid. The coat in this area may be damaged or thinning.
In cases of heavy infestation, the animal may lose weight and appear weakened, as energy is focused on fighting the parasite rather than on growth or reproduction.
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 the larvae of the fly Hypoderma tarandi. The adult female lays her eggs on the reindeer's hair in summer. The hatched larvae penetrate the skin and then migrate inside the body for several months before settling under the skin of the back, where they grow, breathe through a small hole in the skin, then eventually emerge in the spring to fall to the ground and transform into adult flies.
Living in a region where the Hypoderma tarandi fly is present, that is to say the arctic and subarctic areas frequented by reindeer and wild or domestic caribou.
Young animals and weakened animals seem more susceptible to the consequences of heavy infestations.
Hot summers favor the activity of adult flies and therefore the level of infestation.
Herd density and contact with other infested reindeer or caribou increase the risk of exposure to flies.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian makes the diagnosis by observing the characteristic nodules under the skin of the back, especially in winter and spring, when the larvae are well developed.
He can confirm the presence of the larva by examining the breathing opening or by making a small incision to visualize the parasite.
The geographical history of the animal and the season are important elements taken into account, since the disease follows a well-defined annual cycle.
Treatment
Treatment is based on the use of specific antiparasitic products, prescribed and administered by the veterinarian, capable of destroying larvae in migration or already installed under the skin.
In some cases, nodules can be treated locally by veterinary care to avoid infectious complications.
No self-medication should be attempted, the choice of product and timing of treatment being essential for its effectiveness and the safety of the animal.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention is mainly based on antiparasitic treatments applied by the veterinarian at specific times of the year, before the appearance of nodules, to eliminate migrating larvae.
Regular monitoring of the herd makes it possible to identify affected animals and assess the level of infestation from one year to the next.
There is no vaccine against this disease.
Possible complications
A massive infestation can lead to general weakening of the animal, weight loss and reduced production.
Pierced nodules can become secondarily infected by bacteria, causing greater inflammation of the skin.
Damage to the leather is also possible, which can have an economic impact for breeders who add value to the skins.
When to see a veterinarian
Appearance of hard and sensitive nodules under the skin of the animal's back.
Unexplained weight loss or weakening of the reindeer, especially in winter or spring.
Skin lesions that do not heal or appear infected.
Unusual intense agitation behavior during the summer period, which may reflect a fly attack.
Prognosis
The prognosis is generally favorable for lightly infested animals, which naturally eliminate the larvae in the spring without major after-effects.
In the event of a heavy infestation, recovery may be longer and require veterinary support, particularly if infectious complications arise.
A well-conducted antiparasitic treatment, carried out at the right time, significantly improves the comfort of the animal and limits economic losses for the breeder.
Frequently asked questions
Is the reindeer varron dangerous for humans?
No, this disease is specific to reindeer and caribou. It is not transmissible to humans or other common domestic animals.
Why do we see holes in reindeer skin in winter?
These are the breathing holes pierced by the larvae lodged under the skin. Each nodule corresponds to a larva which develops before emerging in the spring.
Can this disease be avoided in farmed reindeer?
A preventive antiparasitic treatment, prescribed by a veterinarian and administered at the right time of year, can significantly reduce the number of larvae that settle under the skin.
Does the infestation heal on its own?
Yes, in the majority of cases the larvae emerge naturally in the spring and the skin heals. But a significant infestation can weaken the animal and require veterinary monitoring.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 15 September 2026
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