Beaver gastrointestinal parasitism (roundworms)

What is it?

Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in beavers, whether European (Castor fiber) or Canadian (Castor canadensis).\n\nThese small parasites live in the intestine of the animal and feed at its expense. In small quantities, they are often well tolerated. But when their numbers increase, or in a weakened animal, they can cause a real digestive disease.\n\nThis parasitosis affects both wild beavers and those kept in captivity (zoological parks, wildlife care centers), with an increased risk in captivity due to promiscuity.

Commonly observed signs

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

Causes and risk factors

The disease is caused by different species of nematodes (roundworms) which colonize the beaver's stomach or intestine. These parasites belong to families close to those found in other semi-aquatic rodents.\n\nThe life cycle of these worms generally goes through a phase in the external environment: the eggs are emitted with the stools, develop in water or soil, then are swallowed by the animal when eating or washing.

Young animals, whose immune system is still immature, are more susceptible.\n\nPromiscuity in captivity, a poorly maintained humid environment, water or litter soiled by feces increase the risk of contamination.\n\nStress, an unbalanced diet or a concomitant disease weaken the natural defenses and favor a more severe infestation.\n\nThe high population density in certain natural habitats or enclosures also favors transmission between individuals.

Transmission

Contamination occurs mainly orally, by ingesting parasite eggs present in water, vegetation, soil or the feces of an infested animal. 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 administration of a suitable antiparasitic medication, prescribed and dosed by the veterinarian depending on the species of parasite identified and the condition of the animal.\n\nNutritional support and rehydration may be additionally necessary in weakened animals.

Prevention

Possible complications

A massive and untreated infestation can lead to severe malnutrition, anemia, and make the animal vulnerable to other diseases. In young people, lasting growth retardation is possible. In rare, severe cases, intestinal obstruction linked to a cluster of worms may occur.

When to see a veterinarian

Prognosis

The prognosis is generally good if the infestation is detected and treated in time. Severe and neglected cases, particularly in young people or already weakened animals, can, however, develop more unfavorably.

Frequently asked questions

References

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

ESCCAP — European Scientific Counsel Companion Animal Parasites

Content reviewed by the TunisieVet editorial team · Updated 17 September 2026