Parasites That Cause Disease in Nonhuman Primates

Pulmonary acariasis (Pneumonyssus spp) is common in wild-caught Asian and African primates, particularly rhesus monkeys and baboons. Infection is rare in laboratory-reared or captive, privately raised nonhuman primates.

The life cycle of Pneumonyssus is not well understood. Infestations usually do not produce serious clinical signs, but they can cause sneezing and coughing. Lesions include dilatation and focal chronic inflammation of terminal bronchioles. On radiographs, gross lesions are occasionally confused with tuberculous granulomas.

Ivermectin (200–500 mcg/kg, SC, PO, IM, once, repeated every 14 days, if needed) has been used to treat Pneumonyssus infestation in closed breeding colonies.

Mange mites (Psorergates spp, Sarcoptes scabiei) or sucking lice (Pedicinus obtusus) occur occasionally, particularly in feral animals, and can produce dermatoses. Ectoparasites can be difficult to find in some animals because of allogrooming, and empirical treatment might be indicated. Systemic treatment with ivermectin (200 mcg/kg, PO, SC, or IM, every 3 weeks), or topical treatment with moxidectin (0.5 mg/kg) or pyrethrin (per product labeling), repeated once after 3 days if necessary, is recommended. Use of more toxic topical parasiticides should be avoided because of the possibility of ingestion during grooming.

Ticks can be present on animals housed outdoors. Although ticks can be difficult to identify on nonhuman primates, because of the primates' habit of manually removing ectoparasites, ticks can transmit diseases such as Lyme disease to nonhuman primates just as they do in humans.

Fleas occur commonly in New World primates that are associated with dogs or cats in the environment. Premise control measures must be instituted, and baths with a pyrethrin-based shampoo temporarily remove fleas from the animal's coat.

Strongyloides and Trichostrongylus are invasive helminths. Adults can cause enteritis and diarrhea; larvae can cause pulmonary lesions during migration. These helminths, as well as Trichuris, can be treated effectively with thiabendazole (100 mg/kg, PO, every 2–4 weeks, until fecal sample results are negative); ivermectin (200 mcg/kg, SC, once, repeated after 14 days); or fenbendazole (50 mg/kg, PO, every 24 hours for 5 days and repeated once after 21 days). Pyrantel pamoate (10 mg/kg, PO, once) is also an option for nematodiasis in New World monkeys and prosimians. The effectiveness of anthelmintic treatment is enhanced by aggressive environmental hygiene practices.

Oesophagostomum can cause characteristic granulomatous nodules in the large bowel wall where the parasites burrow, develop, and incite the host's immune response. The nodules can rupture and cause peritonitis. Albendazole is the treatment of choice, commonly at 7.5 mg/kg, PO, every 24 hours for 3 days.

Prosthenorchis is an acanthocephalan, common in Central and South American nonhuman primates, that burrows into the mucosa of the ileocecal junction and sometimes perforates the bowel or causes obstruction when present in large numbers. Cockroaches are intermediate hosts, and their elimination, along with strict sanitation, is essential for control of infection. Antiparasitic treatment is generally unrewarding.

Dipetalonema and Tetrapetalonema are filarid worms found in the peritoneal cavity of New World primate species. Although moderate numbers can be present with very limited host reaction, peritonitis and general unthriftiness can result from heavy infections. Diethylcarbamazine (20–50 mg/kg, PO, every 24 hours, for 7–21 days) is the treatment of choice when clinical signs occur.

Lungworms such as Filaroides are commonly found in many South American monkeys. Treatment is indicated when identified to prevent pneumonia, potential scarring/fibrosis of the lungs, or exacerbation of other respiratory etiologies. Diethylcarbamazine (50 mg/kg, PO, every 24 hours for 10 days) has been effective.

Bertiella studeri and other enteric cestodes can be found in feral primates and are treated effectively with praziquantel (5 mg/kg, IM, PO, or SC, once). For some cestodes, higher doses of praziquantel (15–20 mg/kg, PO or IM, once) are needed. Somatic larval (cystic) cestodiasis has been reported.

Flukes can cause respiratory, GI, and hematologic signs. Schistosoma spp are trematode blood flukes, whereas Fasciola spp cause hepatic disease and abscessation (more common in Old World primates). The intermediate hosts of flukes are snails and crustaceans, which nonhuman primates ingest through contaminated water or food. Praziquantel (40 mg/kg, PO or IM, once) is effective as treatment.

Nonhuman primates can serve as hosts of various intestinal amoebas. These organisms are the most common type of parasite to cause diarrhea or GI upset in nonhuman primate species.

Entamoeba histolytica is the principal pathogenic amoeba in nonhuman primates (as in humans), causing serious amoebiasis in many species. Entamoeba histolytica infection can be subclinical, but in a heavy infection, E histolytica can cause severe enteritis and diarrhea, and cysts can occur in large numbers in the feces. The fecal trichrome stain is a useful tool to diagnose these infections, which are often overlooked in direct or flotation fecal examinations.

Giardia inhabits the upper small intestine and can produce subclinical infection or cause pale or watery diarrhea in most nonhuman primate species. Treatment with metronidazole (50 mg/kg, PO, every 24 hours for 5–10 days), fenbendazole (50 mg/kg, PO, every 24 hours, for 3 days), or tinidazole (50 mg/kg, PO, every 24 hours, for 3 days) is recommended.

The apicomplexan parasite Cryptosporidium parvum can also cause diarrhea in nonhuman primates, mainly in young animals. C parvum infection is usually self-limiting in immunocompetent hosts. Parenteral fluids and supportive care might be required for young and immunocompromised animals.

Blood parasites, such as Plasmodium, Leishmania, and Trypanosoma spp, also occur in nonhuman primates. Generally, there is an equilibrium between the parasite and the natural host, with infections rarely causing overt disease, outside of myocarditis with ascites in severely immunocompromised animals.

Transmission of simian malarias to humans, although rare, has occurred in areas where the appropriate arthropod vectors are present. Some nonhuman primate species (eg, owl monkeys) are excellent models for research on malaria. Infectious organisms can be identified on a blood smear or via blood culture or PCR assay. Serological assays are available for Trypanosoma cruzi. Treatment with antimalarials will clear circulating infections; however, recrudescence or reinfection can still occur.

Naturally occurring toxoplasmosis (Toxoplasma gondii) has been reported mostly in Central and South American nonhuman primates. It is often highly fatal for squirrel monkeys (Saimiri spp) and ring-tailed lemurs (Lemur catta). Clinical signs of toxoplasmosis tend to be nonspecific (lethargy, anorexia, diarrhea with or without dyspnea), with rapid progression in concentrated populations such as zoos or breeding facilities. Hepatic focal necrosis and fibrinous pneumonia with edema are common histological findings. Toxoplasma can be demonstrated in blood smears in acute cases of infection.