Gastrointestinal parasitism in black bears (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in black bears, both in the wild and in captivity. It mainly involves infestation with ascarids (roundworms similar to those found in dogs) that live in...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in black bears, both in the wild and in captivity. It mainly involves infestation with ascarids (roundworms similar to those found in dogs) that live in the animal's intestines. Most healthy adult bears carry a few worms without showing signs, but a heavy parasite burden can weaken the animal, particularly young cubs which are more vulnerable.
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:
Many infected bears show no visible signs.
When the worm burden becomes heavy, a swollen or bloated belly may be observed, especially in young bears.
The animal may have a reduced appetite, lose weight, or grow more slowly than normal.
The coat may become dull and less shiny.
Vomiting or diarrhea, sometimes with visible worms, may occur.
General fatigue and depression are possible in cases of severe infestation.
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 condition is caused by intestinal nematodes, mainly ascarids belonging to a genus similar to that found in canids, as well as other roundworms that can colonize the bear's intestines. These parasites lay eggs that are passed in the feces, contaminating the environment and potentially being ingested by another bear or by the same animal (reinfection).
Cubs and young bears are more susceptible because their immune system is still immature.
Close contact in captivity, rehabilitation centers, or areas of high wild population density increases the risk of transmission.
An environment soiled by old droppings and poorly cleaned favors the buildup of infective eggs.
A weakened, malnourished, or stressed animal has less resistance to infestation.
Transmission can also occur from mother to offspring, particularly during nursing or through close contact at the den.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian diagnoses the condition by performing fecal analysis (coproscopy) to identify worm eggs under a microscope. In some cases, direct observation of worms in vomit or feces also helps guide the diagnosis. A blood panel may be useful to assess the animal's overall health and check for signs of anemia or malnutrition in cases of severe infestation.
Treatment
Treatment is based on administering antiparasitic medication appropriate for roundworms, prescribed and dosed by the veterinarian according to the animal's weight and condition. Nutritional support may be offered as a supplement if the animal is weak or underweight.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Regular veterinary check-ups with fecal analysis make it possible to detect an infestation before symptoms appear.
In captive settings or rehabilitation centers, frequent enclosure cleaning and prompt removal of feces limit environmental contamination.
Good nutrition and low stress levels strengthen the animal's natural resistance.
Preventive antiparasitic treatments can be established by the veterinarian depending on the circumstances (captivity, rehabilitation, young animals).
Possible complications
In young bear cubs, heavy infestation can cause marked growth delay, dehydration from repeated diarrhea, or even intestinal blockage in extreme cases where the worm mass obstructs the digestive tract. An animal already weakened by other causes (injury, illness, lack of food) tolerates parasitism less well.
When to see a veterinarian
The bear cub or bear has unusual abdominal swelling.
Worms are visible in vomit or feces.
The animal is losing weight or failing to gain weight normally.
Diarrhea or vomiting persists for several days.
The animal appears depressed, weak, or refuses to eat.
Prognosis
The outlook is generally good when infestation is detected and treated promptly, especially in adults. In young cubs or animals already weakened, severe untreated infestation can have more serious consequences for growth and overall health.
Frequently asked questions
Is a black bear carrying roundworms always sick?
No. Many adult bears harbor a few worms with no visible symptoms. The problem mainly occurs when the parasitic load becomes significant, particularly in young animals.
How does a bear catch these worms?
Most often by ingesting parasite eggs present in an environment contaminated with feces, or through transmission from mother to offspring during the first months of life.
Can this parasitism be transmitted to humans?
This risk is not documented in any significant way for this specific parasitic disease of black bears; direct contact with a wild bear should be avoided in any case for many other safety reasons.
Should all captive bears be systematically treated?
The decision rests with the veterinarian, who assesses whether preventive treatment is justified based on faecal analysis results, the animals' age, and housing conditions.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
AVMA — American Veterinary Medical Association
Content reviewed by the TunisieVet editorial team · Updated 26 August 2026
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