Gastrointestinal parasitism in orangutans (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in Bornean orangutans, both in the wild and in captivity. Several species of nematodes can infect the intestines of these great apes, notably ascarids (...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in Bornean orangutans, both in the wild and in captivity. Several species of nematodes can infect the intestines of these great apes, notably ascarids (similar to those found in humans), strongyles, and pinworms. Most animals harbour a low parasite load with no visible signs, but heavy infestation can affect digestive health and overall condition, especially in young or weakened individuals.
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 parasitised orangutans show no outward signs. When worms are numerous, diarrhoea or soft stools may be observed, along with abdominal swelling or tenderness, loss of appetite, progressive weight loss, and a dull coat. Young animals may show delayed growth. In some cases, adult worms are directly visible in the faeces. Massive infestation can cause vomiting, lethargy, and rarely, intestinal obstruction in very young individuals.
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 results from accidental ingestion of nematode eggs or larvae present in the environment (soil, vegetation, contaminated water) or through contact with contaminated faeces. Some roundworm species have a simple direct life cycle (the egg becomes infective in the environment), while others require an intermediate host such as an insect.
Young orangutans, stressed or immunocompromised animals, and those living in densely populated or poorly maintained enclosures are at higher risk. High animal density, inadequate enclosure hygiene, access to areas contaminated with old feces, and contact with parasitized primates increase the risk. In the wild, proximity to areas frequented by humans or other primates can also promote transmission.
Transmission
Transmission occurs mainly through the faecal-oral route, by ingestion of eggs or larvae present on vegetation, in soil, or in water contaminated by infected faeces. Direct contact with faeces from an infested animal is the primary source of contamination.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian bases diagnosis on clinical observation and especially on a fecal examination (microscopic analysis of stool) to identify parasite eggs and estimate parasite load. Additional tests such as blood work (screening for anemia or inflammatory signs) or abdominal ultrasound may be performed if complications are suspected.
Treatment
Treatment involves administration of antiparasitic drugs (dewormers) tailored to the identified nematode species, under strict veterinary supervision given the species' sensitivity. Nutritional support and rehydration may be provided in cases of weight loss or severe diarrhea. Treatment is always accompanied by environmental sanitation to prevent immediate reinfection.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention relies on strict enclosure and living space hygiene: regular cleaning, prompt fecal removal, and soil moisture management. A preventive deworming program and regular parasitological monitoring of feces (fecal examination) allow detection and treatment of infestations before clinical signs appear. Quarantine and screening of new arrivals to a group limit the introduction of new parasites. Good management of animal density and water quality also help reduce risk.
Possible complications
Heavy untreated infestation can cause dehydration, anemia, growth delays in young animals, or even intestinal obstruction in severe cases. Weakened or immunocompromised animals are at higher risk of severe complications.
When to see a veterinarian
Persistent diarrhea or abnormal stools lasting several days
Visible worms in the feces
Unexplained weight loss or loss of appetite
Swollen, hard, or visibly painful abdomen
Marked lethargy or repeated vomiting
Growth delay in a young animal
Transmission to humans
Some species of intestinal roundworms found in orangutans, particularly roundworms similar to those seen in humans, can potentially spread to people through accidental ingestion of infective eggs, especially with close contact or poor hygiene. The risk remains limited but justifies hygiene precautions for caregivers and visitors in close contact.
Prognosis
The outlook is generally good when the infestation is caught early and treated promptly, with return to normal health. Severe or neglected cases, particularly in young animals or those already weakened, can lead to more serious complications requiring intensive care.
Frequently asked questions
Is an orangutan that carries worms necessarily sick?
No. A low parasitic burden is often well tolerated and causes no visible signs. It is mainly a heavy infestation that can impact health.
How can you tell if an orangutan is infested with parasites?
The diagnosis is based primarily on a microscopic examination of stool samples performed by a veterinarian, which allows for the detection of parasite eggs even in the absence of visible signs.
Can you catch these worms through contact with an orangutan?
The risk exists but remains limited. Some of the orangutan's nematodes are similar to those found in humans, and transmission is theoretically possible in cases of close contact with contaminated feces, which underscores the importance of hygiene measures.
Should all captive orangutans be systematically dewormed?
Many zoos implement regular parasitological monitoring and preventive worming programmes tailored by the veterinary team based on faecal analysis results.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
CDC — Centers for Disease Control and Prevention
ESCCAP — European Scientific Counsel Companion Animal Parasites
Content reviewed by the TunisieVet editorial team · Updated 29 August 2026
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