Parasitic Diseases of Nonhuman Primates
Newly imported nonhuman primates harbor numerous parasites. Some are commensal; others can be made self-limiting by strict sanitation and good husbandry. However, some can cause serious diseases or debilitation and should be removed by specific treatment. Captive-raised New World primates housed indoors (ie, with their caretakers) are rarely found to have intestinal parasites; however, this may not be the case when they associate with sandboxes and various outdoor enclosures. Fecal examinations should be part of the routine clinical annual examination.
Pulmonary acariasis (Pneumonyssus spp) is common in wild-caught Asian and African primates, particularly rhesus monkeys and baboons. Infection is rare in laboratory-raised or captive, privately raised nonhuman primates. The life cycle of Pneumonyssus spp is not well understood. Infestations usually do not produce serious symptomatic disease, although they may cause sneezing and coughing. Lesions include dilation and focal chronic inflammation of terminal bronchioles. The gross lesions may occasionally be confused with tuberculous granulomas. Ivermectin (200 mcg/kg, SC, PO, IM, repeated in 14 days) has been used for treatment in closed breeding colonies.
Mange mites (Psorergates spp, Sarcoptes scabiei) or sucking lice (Pedicinus obtusus) are seen occasionally, particularly in feral animals, and may produce dermatoses. Systemic treatment with ivermectin, 200 mcg/kg, PO, SC, IM, repeated every 3 wk, or topical treatment with pyrethrin, repeated after 3 days if necessary, is recommended. Use of more toxic topical parasiticides should be avoided because of the possibility of ingestion during grooming. Fleas are commonly seen 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 will temporarily remove fleas from the animal's haircoat.
Oesophagostomum may cause characteristic granulomatous nodules in the large bowel associated with development of the worms and with an immune reaction of the host. The nodules may rupture and cause peritonitis. Strongyloides and Trichostrongylus are invasive—adults may cause enteritis and diarrhea, larvae may cause pulmonary lesions during migration. These helminths, as well as Trichuris, can be treated effectively with thiabendazole at 100 mg/kg, administered PO at intervals of 2–4 wk; ivermectin at 200 mcg/kg, SC, repeated in 14 days; or febendazole at 50 mg/kg/day, PO, for 3 days and repeated in 14 days. The effectiveness of anthelmintic treatment is enhanced by aggressive environmental hygiene practices. 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. Dipetalonema and Tetrapetalonema are filarid worms found in the peritoneal cavity of New World species; large numbers may be present with very limited host reaction. Lungworms such as Filaroides are commonly found in many South American monkeys.
Bertiella studeri and other enteric cestodes may be found in animals of feral origin and are treated effectively with praziquantel (5 mg/kg, IM, PO, or SC, once). For some cestodes, 15–20 mg/kg, PO or IM, once, will be needed. Somatic larval (cystic) cestodiasis has been reported. Flukes may cause respiratory, GI, and hematologic signs. Schistosoma sp is a blood fluke, whereas Fasciola sp infect the liver and may cause hepatic disease and abscessation (more common in Old World primates). The intermediate hosts are snails and crustaceans, which are ingested through contaminated water or food. This is of zoonotic concern. Praziquantel at 40 mg/kg, PO or IM, in a single dose has been effective.
Nonhuman primates may serve as hosts of various intestinal amebae. Entamoeba histolytica is the principal pathogenic form in nonhuman primates (as in people). It has only rarely been reported as pathogenic in monkeys, mostly in South American spider and woolly monkeys. However, it can be a serious infection in marmosets and has caused serious enteritis in great apes. In a heavy infection, it may cause severe enteritis and diarrhea, and cysts may be demonstrated in the feces in large numbers. The fecal trichrome stain is a useful tool to diagnose these types of infections, which are often overlooked in a direct or flotation fecal examination. Giardia inhabit the upper small intestine and may cause watery diarrhea. Treatment with metronidazole (50 mg/kg/day, PO, for 5–10 days) is recommended. Cryptosporidium parvum may also cause diarrhea in nonhuman primates, mainly in young animals. Successful treatment in marmosets with paromomycin has been reported. This infection is usually self-limiting in immunocompetent hosts.
Blood parasites, such as Plasmodium, Leishmania, and Trypanosoma spp, are also found. Generally, there is an equilibrium between the parasite and the natural host, with infections rarely causing overt clinical disease. Transmission of simian malarias to people, although rare, has occurred in areas where the appropriate mosquito vectors are present. Some nonhuman primate species (eg, owl monkeys) are excellent models for malarial research.
Naturally occurring toxoplasmosis (Toxoplasma gondii) has been reported in Central and South American primates. Clinical signs of infection tend to be nonspecific (lethargy, anorexia, diarrhea). Hepatic focal necrosis and fibrinous pneumonia with edema are common histologic findings. Toxoplasma can be demonstrated in blood smears in acute cases. (See also Toxoplasmosis.)