Gastrointestinal parasitism in polar bears (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a common digestive condition in polar bears, both in the wild and in zoos. These parasites live in the animal's intestines and feed at the animal's expense, which can weaken it...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a common digestive condition in polar bears, both in the wild and in zoos. These parasites live in the animal's intestines and feed at the animal's expense, which can weaken its overall health, especially in young individuals or weakened animals. In most cases, the infestation remains mild and well tolerated, but it can become problematic when the number of parasites is high or when the bear is already stressed or ill.
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:
Clinical signs are often mild, especially with light infestation. Diarrhea (sometimes chronic), occasional vomiting, a dull and less glossy coat, loss of appetite, or conversely a normal appetite despite gradual weight loss may be observed. In young cubs, growth retardation or a swollen belly may be noted. In heavy infestations, worms or worm fragments may sometimes be visible directly in the stool. Overall lethargy and poor condition are possible when the parasite burden is high.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Infestation is caused by intestinal nematodes (roundworms), some species of which are shared with other carnivores or are closely related to species found in brown bears. The bear becomes infected by ingesting eggs or larvae present in the environment, in water, or through consuming prey (fish, seals, carrion) carrying infective larvae. Transmission can also occur from mother to cubs, particularly during nursing for certain worm species.
Young bears, particularly recently weaned cubs, are more susceptible due to an immature immune system. Stress, captivity, crowding with other animals, unbalanced nutrition, or a poorly maintained environment with repeated fecal contamination increase the risk of parasite buildup. Animals weakened by other diseases or malnutrition are also more vulnerable to severe infestations.
Transmission
Infection occurs mainly through the mouth, by ingesting worm eggs present in the environment (soil, contaminated snow, water) or by consuming prey carrying larvae (fish, seals). Transmission from mother to cubs can also occur, particularly through milk for certain parasites.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is based on microscopic examination of feces (fecal flotation), which reveals parasite eggs. The veterinarian may also look for adult worms directly visible in the stool. Blood work can be useful to assess the overall impact of infestation, including anemia and nutritional status. In some cases, abdominal ultrasound may be added to the evaluation.
Treatment
Treatment consists of antiparasitic medication (anthelmintics) suited to the species and parasite type identified, prescribed only by a veterinarian. Nutritional support may be given if significant weight loss occurs. Follow-up testing with another fecal examination verifies treatment effectiveness.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention depends on good enclosure and environmental hygiene, with regular cleaning of areas soiled by feces. Regular veterinary check-ups with fecal examination allow early detection of infestation. A preventive worming program tailored by the veterinarian can be established, especially for young animals or those in captivity. High-quality nutrition also helps maintain the animal's natural resistance.
Possible complications
With severe untreated infestation, possible complications include anemia, dehydration from chronic diarrhea, marked growth retardation in young animals, and general weakness that makes other infections more likely. In rare severe cases, intestinal obstruction from worm accumulation can occur in young animals.
When to see a veterinarian
Persistent or worsening diarrhea
Unexplained weight loss despite normal appetite
Visible worms in the stool
Swollen or tender abdomen in a cub
Marked lethargy linked to digestive upset
Prognosis
The prognosis is generally good when the infestation is detected and treated promptly, especially in healthy adults. In young animals or those already weakened, a heavy untreated infestation can have more serious consequences for growth and overall condition, but remains usually favorable with appropriate care.
Frequently asked questions
Can a polar bear in captivity catch worms even without contact with other animals?
Yes, because parasite eggs can persist for a long time in the environment (soil, water, enclosures) and contaminate the animal regardless of direct contact with another infested animal.
Is gastrointestinal parasitism dangerous for the adult bear?
In healthy adults, infestation often remains subtle and well tolerated. It becomes more concerning in cases of high parasitic burden or if the animal is already weakened.
How do you know if a polar bear has worms?
Diagnosis is made through a veterinary examination of feces under a microscope, which allows parasitic eggs to be detected, even when no visible signs are present.
Should all polar bears in zoos be systematically dewormed?
The decision rests with the park's veterinarian, who adjusts the worming frequency based on faecal examination results and the facility's health status.
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 30 August 2026
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