Gastrointestinal Parasitism in Siamangs (Roundworms)
The siamang is a large gibbon native to the forests of Southeast Asia, often housed in zoological parks. Like many primates, it can harbor roundworms (nematodes) in its digestive tract. These parasites live in the intestine and feed at the...
What is it?
The siamang is a large gibbon native to the forests of Southeast Asia, often housed in zoological parks. Like many primates, it can harbor roundworms (nematodes) in its digestive tract. These parasites live in the intestine and feed at the animal's expense, causing progressive deterioration of its general condition. Infestation is common both in captivity and in the wild, but becomes problematic when the parasite burden is high or the animal is already in a weakened state. Good enclosure hygiene and regular veterinary monitoring help limit this risk.
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:
Signs are often subtle at first, especially if few worms are present. Diarrhea or soft stools may be observed, sometimes accompanied by worms visible to the naked eye. The animal may lose appetite, lose weight gradually, and develop a dull coat that is less well-maintained. A swollen or bloated abdomen, general fatigue, and lack of enthusiasm are also possible. In young siamangs, growth retardation may appear if the infestation is long-standing or severe. In severe cases, dehydration and marked lethargy may develop.
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 gastrointestinal nematodes, a group of roundworms that includes in particular ascarids, strongyles, or pinworms depending on the species encountered in primates. These parasites lay eggs that are shed in the feces of the infested animal. Other siamangs or animals sharing the enclosure may then become infested by ingesting these eggs, present on the ground, food, or contaminated water. Some parasite cycles also involve passage through the soil or through an intermediate host before becoming infectious again.
Young animals, debilitated or immunocompromised individuals are more prone to severe infestation.
A poorly maintained enclosure with accumulation of fecal matter promotes parasite egg survival in the environment.
Crowding with other primates, unchanged soil, and insufficient hygiene of water or food also increase risk.
Stress, environmental changes, or unbalanced diet can weaken the animal and worsen symptoms.
Transmission
Transmission occurs mainly by the fecal-oral route, that is, by accidental ingestion of parasite eggs present in an environment contaminated by infested feces. The ground, water, food, or objects in the enclosure may be contaminated. Some parasites require a maturation period in the external environment before becoming infectious.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is mainly established through microscopic fecal examination, called fecal flotation, to detect worm eggs.
Multiple samples may be needed because egg shedding is not always constant.
A complete clinical examination assesses the animal's general condition, hydration, and weight.
In some cases, additional blood tests help evaluate the impact of infestation on the body.
Treatment
Treatment relies on antiparasitic agents from the deworming family, selected by the veterinarian based on the worm type identified.
Nutritional support and rehydration may be given if the animal is weakened.
Complete environmental cleanup is essential alongside treatment to prevent rapid reinfection.
Post-treatment fecal examination verifies the effectiveness of the protocol chosen by the veterinarian.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Regular and thorough enclosure cleaning with frequent removal of feces substantially reduces contamination risk.
Disinfecting surfaces and limiting stagnant moisture, which favors parasite egg survival, is advised.
Regular fecal tests performed by a veterinarian allow detection of infestation before symptoms appear.
A preventive deworming program, tailored by the veterinarian to the facility or sanctuary setting, is often recommended.
Isolating new arrivals during parasitic screening also limits the introduction of new parasites to the group.
Possible complications
Untreated heavy infestation can lead to anemia, severe weight loss, and general weakening of the animal.
Young animals may experience lasting growth retardation.
In rare cases, intestinal obstruction from a mass of worms can occur, which constitutes an emergency.
Chronic infestation also weakens the immune system, making the animal more vulnerable to other diseases.
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 or painful abdomen to the touch
Marked lethargy or apparent dehydration
Growth retardation in a young siamang
Transmission to humans
Some intestinal roundworms from primates can, in rare cases, infest humans, particularly animal care staff or visitors in close contact with the animals or their feces.
Adherence to basic hygiene measures, such as handwashing after any contact with the enclosure, limits this risk.
Wearing gloves during enclosure cleaning is recommended for animal care personnel.
Prognosis
The prognosis is generally favorable when infestation is detected and treated early.
Appropriate treatment combined with good enclosure hygiene usually results in complete recovery.
The prognosis becomes more guarded in cases of heavy, chronic infestation, or in an animal already weakened by other causes.
Frequently asked questions
Can a symptomatic siamang contaminate other zoo animals with worms?
Yes, if the enclosure is shared or poorly maintained, parasite eggs present in feces can contaminate other primates or susceptible animals nearby.
Should a siamang be dewormed even without visible symptoms?
Yes, regular parasitological screening is recommended because many infected gibbons show no visible signs, especially in the early stages.
Is gastrointestinal parasitism dangerous for humans?
The risk exists but remains limited with good hygiene practices; handwashing and wearing gloves when cleaning enclosures are generally sufficient to protect against it.
How long does antiparasitic treatment last?
The duration and exact protocol are determined by the veterinarian based on the type of worm identified and the severity of the infestation; a stool examination is then performed to verify the effectiveness of the treatment.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
ESCCAP — European Scientific Counsel Companion Animal Parasites
CDC — Centers for Disease Control and Prevention
Content reviewed by the TunisieVet editorial team · Updated 02 September 2026
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