Reindeer gastrointestinal parasitism (roundworms)

What is it?

Gastrointestinal parasitism of reindeer includes infestations by roundworms (nematodes) which live in the stomach and intestine of the animal. These parasites are very common in reindeer kept in herds, especially in arctic and subarctic regions.\n\nThey do not always cause visible disease. But when the parasitic load becomes significant, especially in young animals or during periods of nutritional stress, they can cause real weight loss and weaken the entire herd.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

Several species of gastrointestinal nematodes can infest reindeer, including worms in the abomasum (one of the compartments of the stomach) and the intestine. The eggs of these worms are passed in the stool, develop in the external environment and then are swallowed by the animal when grazing on lichen or contaminated vegetation.\n\nInside the host, the larvae transform into adult worms which attach themselves to the digestive wall, feed on blood or tissues, and disrupt digestion and absorption of nutrients.

Young animals (fawns) are more vulnerable because their immunity to parasites is not yet mature.\n\nThe high density of the herd favors contamination of the pasture by eggs and larvae. Climatic conditions also play a role: a mild and humid spring or summer favors the development of infesting larvae on the pasture.\n\nNutritional stress, particularly at the end of winter when fat reserves are low and available lichen is reduced, reduces the animal's defenses against parasites.\n\nRepeated movement on the same pastures without sufficient rest of the land also increases the risk of infestation.

Transmission

Contamination occurs orally: the animal ingests infective larvae present on lichen or pasture vegetation, contaminated by the feces of carrier animals. There is no direct transmission between animals without passing through the external environment.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

Treatment is based on the use of appropriate antiparasitic medications (wormers), prescribed and dosed by the veterinarian depending on the parasitic species identified and the situation of the herd.\n\nNutritional support treatment may be combined to help weakened animals replenish their reserves. The decision to treat the entire herd or only the most affected animals depends on the veterinary assessment of the overall parasite load.

Prevention

Possible complications

A severe and untreated infestation can lead to marked weight loss, significant anemia and general weakening which makes the animal more vulnerable to other diseases or to winter cold.\n\nIn fawns, significant growth retardation can compromise their survival during the first winter. In extreme cases, the combination of parasitism with a harsh winter or lack of food can lead to death.

When to see a veterinarian

Prognosis

The prognosis is generally good if the infestation is detected and treated in time, with good recovery of body condition. It becomes more reserved in animals already weakened by cold, undernutrition or young age, where complications can be serious or even fatal.

Frequently asked questions

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

ESCCAP — European Scientific Counsel Companion Animal Parasites

FAO — Organisation des Nations unies pour l'alimentation et l'agriculture

Content reviewed by the TunisieVet editorial team · Updated 15 September 2026