Primate Parasites: Internal and External – NAVLE Study Guide

Overview and Clinical Importance

Parasitic infections in non-human primates (NHPs) represent a significant health concern in captive and wild populations, with important zoonotic implications for animal handlers and veterinarians. Both internal parasites (helminths and protozoa) and external parasites (ectoparasites) can cause substantial morbidity and mortality in primate populations. Understanding these parasites is essential for the NAVLE examination, particularly regarding diagnosis, treatment, and prevention strategies.

Internal Parasites: Helminths

Nematodes (Roundworms)

Strongyloides fulleborni (Threadworm): Prevalence of 44.8% in some African NHP populations. Causes diarrhea, weight loss, and in severe cases, disseminated strongyloidiasis in immunocompromised animals. Diagnosis via larvae in feces using Baermann technique or fecal flotation. Transmitted through skin penetration or ingestion of contaminated food/water.

Trichuris spp. (Whipworm): Most predominant helminth in captive primates (63.5% prevalence reported). Adult worms reside in cecum and colon. Clinical signs include mucoid diarrhea, anemia, and rectal prolapse in heavy infections. Eggs are barrel-shaped with bipolar plugs on fecal flotation.

Oesophagostomum spp. (Nodular worm): Causes nodular lesions in the large intestine. Clinical signs include diarrhea and weight loss. Prevalence approximately 15.2% in African NHPs. Diagnosis through identification of eggs in feces and visualization of nodules on necropsy.

Enterobius vermicularis (Pinworm): Causes perianal pruritus. Adult females migrate to perianal area to deposit eggs. Diagnosis using cellophane tape test. More common in captive populations.

Ascaris spp.: Large roundworms causing intestinal obstruction in heavy infections. More common in young animals. Eggs are thick-shelled and easily identified on fecal flotation.

Trematodes and Cestodes

Schistosoma mansoni: Blood fluke affecting Old World primates in endemic areas. Prevalence approximately 4.3% in some populations. Causes hepatosplenomegaly and portal hypertension. Eggs with lateral spine found in feces or urine depending on species.

Cestodes are less commonly reported in primates but can include various species transmitted through ingestion of intermediate hosts.

Internal Parasites: Protozoa

Protozoan parasites are often more prevalent than helminths in many primate populations, with overall prevalence reaching 47.3% in some zoological institutions.

Amoebae

Entamoeba histolytica: Pathogenic amoeba causing amoebic dysentery with bloody diarrhea and flask-shaped colonic ulcers. Prevalence 24.8% in some populations. Cysts have 1-4 nuclei with central karyosome and fine peripheral chromatin. Zoonotic - can infect humans.

Entamoeba coli: Non-pathogenic commensal. Most prevalent protozoan (64.8% in some studies). Cysts have greater than 4 nuclei (typically 8) with eccentric karyosome and coarse peripheral chromatin. Important to differentiate from E. histolytica.

Flagellates

Giardia duodenalis: Causes acute or chronic diarrhea, weight loss, and malabsorption. Cysts are oval with 4 nuclei and median bodies visible on iodine stain. Trophozoites have characteristic 'falling leaf' motility. Zoonotic genotypes can transmit between primates and humans.

Ciliates

Balantidium coli: Large ciliated protozoan (40.3% prevalence in some populations). Causes balantidiasis with dysentery. Trophozoites are large, ciliated, with visible macronucleus and micronucleus. Zoonotic potential from primate handlers.

Coccidia and Other Protozoa

Cryptosporidium spp.: Causes watery diarrhea, especially in immunocompromised animals. Oocysts are small (4-6 micrometers), acid-fast positive on modified Ziehl-Neelsen stain. Zoonotic.

Cyclospora spp.: Larger than Cryptosporidium (8-10 micrometers). Autofluorescence under UV light. Causes cyclosporiasis with prolonged diarrhea.

Enterocytozoon bieneusi: Microsporidian causing chronic diarrhea and wasting in immunocompromised primates. Requires special staining (modified trichrome) or molecular diagnostics for identification.

Diagnostic Methods for Internal Parasites

External Parasites: Ectoparasites

Ectoparasites in non-human primates include ticks, mites, lice, and fleas. These parasites can cause direct damage through blood feeding, dermatitis, and pruritus, as well as serve as vectors for various zoonotic diseases.

Ticks (Acari: Ixodidae and Argasidae)

Common genera: Haemaphysalis, Ixodes, Amblyomma, Rhipicephalus. Ticks are three-host parasites that feed on blood at each life stage (larva, nymph, adult). Clinical significance includes anemia, tick paralysis, and transmission of pathogens (Babesia, Ehrlichia, Borrelia).

Diagnosis: Visual identification on physical examination. Ticks typically attach in areas with thin skin (ears, axilla, groin). Remove ticks carefully to avoid leaving mouthparts embedded.

Mites

Sarcoptic mange (Sarcoptes scabiei): Burrowing mite causing intense pruritus, alopecia, and crusting lesions. Lesions typically start on face, ears, and limbs. Highly contagious and zoonotic. Diagnosis via skin scraping revealing mites, eggs, or fecal pellets.

Laelaptidae (gamasid mites): Free-living or parasitic mites found on primates. Can cause dermatitis and transmit pathogens. Collected by combing fur.

Trombiculidae (chigger mites): Larval stages are parasitic. Cause pruritic papules and dermatitis. Seasonal prevalence in wild populations. Microscopic identification required.

Lice (Phthiraptera)

Lemurpediculus spp. (sucking lice): Found on lemurs and other primates. Feed on blood causing anemia in heavy infestations. Diagnosis through visual identification or combing. Eggs (nits) attached to hair shafts.

Clinical signs: Pruritus, alopecia, anemia in heavy infestations, secondary bacterial infections. Lice are host-specific and transmitted by direct contact.

Fleas

Less common in primates than in other mammals. When present, can cause flea allergy dermatitis and transmit pathogens. Echidnophaga gallinacea (sticktight flea) has been reported in some primate species.

Treatment and Management

Antiparasitic Drugs for Internal Parasites

Ectoparasite Control

Topical treatments: Ivermectin (pour-on or injectable), fipronil, selamectin for mites and lice. Multiple treatments typically required (14-21 day intervals) to break lifecycle.

Environmental management: Thorough cleaning and disinfection of enclosures, bedding replacement, treatment of all animals in contact to prevent reinfection.

Tick removal: Manual removal using fine-tipped forceps, grasping as close to skin as possible. Avoid crushing tick body to prevent pathogen transmission.

Exam Focus: Know that macrocyclic lactones (ivermectin) are effective against both internal nematodes and external parasites, making them useful for comprehensive parasite control programs in primate facilities. However, repeated use can select for resistance.

Prevention and Biosecurity

Quarantine Protocols

• Minimum 30-60 day quarantine for new arrivals
• Multiple fecal examinations during quarantine period (minimum 3 samples)
• Complete physical examination including ectoparasite screening
• Prophylactic deworming upon arrival and before release from quarantine

Routine Screening Programs

Annual fecal examinations for all captive primates. More frequent screening (quarterly) for breeding colonies or research facilities. Old World Monkeys show higher parasite prevalence (93.6%) compared to New World Monkeys (40.0%) and prosimians (37.1%), requiring more intensive monitoring.

Zoonotic Disease Prevention

Critical zoonotic parasites: Strongyloides fulleborni, Entamoeba histolytica, Balantidium coli, Giardia duodenalis, Cryptosporidium spp., Schistosoma mansoni.

Handler protection:

• Personal protective equipment (gloves, gowns) when handling primates or fecal material
• Hand hygiene protocols strictly enforced
• Immunocompromised individuals should avoid primate contact
• Prompt fecal removal and proper disposal