Gastrointestinal parasitism in macaques (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in Barbary macaques, whether living in parks, sanctuaries, or semi-free settings. Several species of roundworms can colonize the intestines of these pri...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a very common condition in Barbary macaques, whether living in parks, sanctuaries, or semi-free settings. Several species of roundworms can colonize the intestines of these primates, including pinworms, ascarids, and strongyles. These parasites live at the animal's expense, feeding on intestinal contents or blood, and interfere with digestion. The disease is particularly common in young animals and in groups living in crowded captive conditions.
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 macaques show no visible signs, especially if the infestation is light.
When signs do appear, diarrhea or soft stools are most often observed, sometimes with mucus.
The coat becomes dull and the animal gradually loses weight despite sometimes maintaining an appetite.
In young individuals, stunted growth and a swollen or tender belly may be noted.
With heavy infestations, whole worms may be seen in the stools or around the anus.
General fatigue, lethargy, and sometimes vomiting complete the clinical picture.
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 disease is caused by the presence of intestinal nematodes, unsegmented roundworms that settle in the stomach or intestines of the macaque. The most commonly reported species in macaques include pinworms (such as Enterobius), ascarids (similar to Ascaris lumbricoides), and various strongyles. These parasites lay eggs that are shed in feces, which then contaminate the environment.
Young animals, weakened or immunocompromised individuals, and those housed in overcrowded or poorly maintained enclosures are most at risk. Soiled ground, poor faeces management, contaminated water or food also increase risk. Stress from captivity can heighten susceptibility to parasites.
Transmission
Transmission occurs mainly through the fecal-oral route: the animal ingests eggs or larvae present on the ground, food, water, or objects soiled by infected feces. Scratching of itchy anal areas (in the case of pinworms) can also promote self-reinfection. Close contact between individuals in an enclosure or colony greatly facilitates transmission.
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 faecal microscopy (examination of stool under the microscope) to detect parasite eggs. The veterinarian may also look for adult worms visible in the faeces or perform a tape test for pinworms. In some cases, a blood test helps assess the overall impact of the infestation.
Treatment
Treatment consists of administering antiparasitic drugs (dewormers) prescribed and adjusted by the veterinarian according to the parasite species identified. Supportive treatment (rehydration, nutritional supplements) may be given if the animal is markedly weakened. Treatment of the entire group is often necessary to prevent reinfestation.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Regular and thorough cleaning of enclosures, with frequent removal of faeces, significantly reduces environmental contamination. Faecal examinations to screen for parasites are recommended periodically by a veterinarian, even without symptoms. Quarantine and parasite screening of new arrivals before introduction into the group are essential. Good hygiene of water and feed complete these measures.
Possible complications
Untreated heavy infestation can lead to anaemia, severe dehydration, persistent poor growth in young animals, or intestinal obstruction in extreme cases. The weakened animal also becomes more vulnerable to other infections.
When to see a veterinarian
Persistent diarrhoea or abnormal stools.
Worms visible in faeces or around the anus.
Progressive weight loss despite normal appetite.
Swollen or painful abdomen, especially in young animals.
Lethargy, unusual fatigue, or dull coat lasting.
Transmission to humans
Some roundworms in macaques, particularly pinworms and ascarids, can potentially be transmitted to humans, especially in caretakers or visitors in close contact with the animals or their faeces. Proper hygiene measures (hand washing, wearing gloves) are recommended when handling animals or cleaning enclosures.
Prognosis
The prognosis is generally good when infection is detected early and treated properly, with complete recovery in the majority of cases. It becomes more guarded in young animals or weakened individuals if the parasite burden is heavy and neglected, with a risk of more serious complications.
Frequently asked questions
Can a parasitized macaque show no symptoms?
Yes, it's common in cases of light infestation. Only a stool examination by a veterinarian can confirm it.
Can this parasitism be transmitted to humans?
Some roundworms of macaques are zoonotic. Good hand hygiene after contact with the animal or its feces is therefore recommended.
Should you deworm the entire group or only the sick animal?
In captivity, it is often recommended to treat the entire group, as environmental contamination readily affects all individuals.
How to prevent infestation from returning?
Regular cleaning of enclosures, prompt removal of feces, and regular parasitological checks significantly reduce the risk of reinfection.
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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