Gastrointestinal parasitism of hamadryas (roundworms)

What is it?

Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in the hamadryas, a baboon native to the Horn of Africa and the Arabian Peninsula, often housed in zoological parks. These worms, like strongyles, roundworms or pinworms, live in the monkey's intestine and feed at its expense. They settle particularly well in groups living in captivity, where promiscuity and repeated contact with excrement favor their transmission from one individual to another. Parasitism can remain discreet in a healthy animal, but become problematic in young, weakened or stressed animals.

Commonly observed signs

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

Causes and risk factors

Several species of roundworms (nematodes) can parasitize the digestive tract of hamadryas, including strongyles, roundworms and sometimes pinworms. These parasites lay eggs which are passed in the stools of the infested animal. In the environment, these eggs become infective after a certain time, then are ingested by another individual who in turn becomes infected, often by bringing contaminated hands or food to the mouth. The cycle thus closes in a loop within the group, particularly in the enclosures where hygiene is difficult to maintain perfectly.

Living in groups and in enclosed spaces, typical of zoological parks, strongly favors the transmission of roundworms between hamadryas. Young animals, whose immune systems are still immature, are more vulnerable to severe forms. A poorly maintained enclosure, with an accumulation of fecal matter or damp bedding, increases the risk of infestation. Stress, linked to a change in environment, overpopulation or an unstable social hierarchy, can weaken natural defenses and encourage the development of parasites already present. The introduction of a new animal not parasitologically controlled also represents a risk factor for the entire group.

Transmission

Transmission occurs via the fecal-oral route: the animal ingests worm eggs present in the contaminated environment (soil, food, water) after their excretion by a parasitized individual. Close contact between animals in captive groups promotes rapid cross-contamination.

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 antiparasitics belonging to the family of broad-spectrum dewormers, chosen by the veterinarian according to the parasite(s) identified. Supportive treatment can be combined in the event of dehydration or marked weight loss, with rehydration and nutritional support. In captive groups, collective treatment of all individuals is often recommended to avoid rapid reinfestation from asymptomatic carrier animals.

Prevention

Possible complications

Heavy, prolonged infestation can lead to anemia from chronic blood loss or poor nutrient absorption. In young animals, lasting growth retardation is possible. In severe cases, dehydration linked to severe diarrhea can be life-threatening, particularly in animals already weakened by other diseases or by young age.

When to see a veterinarian

Transmission to humans

The risk of transmission to humans is considered low but not zero for certain nematodes shared between primates. Compliance with standard hygiene measures (hand washing, wearing gloves) by personnel in contact with animals or their droppings is generally sufficient to limit this risk.

Prognosis

The prognosis is generally favorable when the infestation is detected early and treated appropriately. Most animals recover completely after proper antiparasitic treatment. The prognosis becomes more guarded in very weakened young animals or in the event of delay in treatment, due to the risk of dehydration and secondary complications.

Frequently asked questions

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 23 September 2026