Joseph A. Smith, DVM
Primates are a diverse taxa that presents unique clinical challenges to the veterinarian. The purpose of this presentation is to introduce the clinician to basic preventative medical procedures and the common diseases associated with non-human primates, with an emphasis on monkeys. More extensive references on primate medicine are available.2-5 The ethics of treating pet primates is highly debated, and should be a consideration that is thoroughly considered prior to the decision to get involved with pet primates. The clinician should also be familiar with the regional and local legal restrictions on primates and how they affect veterinary care of those species.
Primates pose a safety risk due to their ability to inflict serious trauma and due to their zoonotic disease potential. Proper training, including disclosure of risks, should be provided to all hospital personnel, including non-medical staff. The hospital must be equipped with proper equipment, drugs, housing, and personal protective equipment (PPE) to accommodate primate patients. The decision to incorporate primates into a clinical practice should not be taken lightly. Extensive planning, preparation, and training should occur before the first primate patient is ever admitted.
Humans and primates share many infectious diseases. Proper training of staff, procedures for handling animals and samples, and proper PPE can all help to reduce the risk of acquiring a zoonotic disease from primates. Annual tuberculosis (TB) testing of staff is recommended for patient and staff safety. Vaccination of staff for hepatitis B, tetanus, and rabies is recommended. Many labs will not accept primate diagnostic samples due to the zoonotic disease risk, so be sure to check before shipping samples.
With rare exceptions, a thorough physical exam of a primate will require sedation or anesthesia. This also helps to maintain the safety of the clinician and staff and reduces stress to the patient. Primate anatomy can vary greatly, so the clinician should be familiar with each species treated. Scent gland locations, dentition, and gastrointestinal anatomy are some of the features that can vary greatly between taxa. A systematic exam of each body system should occur with every exam, including a thorough oral/dental exam.
Blood is routinely collected from the femoral, brachial, or saphenous veins. The femoral vein is located medial to the palpable femoral artery located in the inguinal region with the leg extended caudally. Holding off this vessel is rarely required. Pressure should be applied afterward to prevent hematoma formation. The brachial vein (ventral surface of the forearm) and saphenous vein (caudal surface of the distal rear limb) are alternative sites for venipuncture and are the preferred sites for IV catheters. Closed collection systems (e.g., Vacutainer brand) are recommended for venipuncture to reduce the risk of exposure to blood. Needles should not be recapped prior to disposal in a sharps container.
TB Testing & Ancillary Diagnostics
Annual TB testing is recommended for all primates. A tuberculin syringe with 25–27 gauge needle is used to inject 0.1 ml of mammalian old tuberculin intradermally in an atraumatic manner. The most common injection site is the upper eyelid, although other sites such as the abdomen have been used. The site should be observed for swelling and erythema 24, 48, and 72 hours post-injection. Any swelling or erythema should be considered a suspect reaction and be followed up with additional diagnostics. Ancillary TB diagnostics include comparative skin testing, thoracic radiography, gastric or bronchoalveolar lavage for mycobacterial PCR or culture, gamma interferon testing, and serologic testing.
Radiographs are a useful screening as well as diagnostic tool. Standard orthogonal positioning applies to primates, except that larger species (e.g., apes) may produce better thoracic images in an upright position.
Annual vaccination for rabies using a killed vaccine is routinely performed. However, this is off-label use and vaccinated primates may be treated as unvaccinated by authorities in cases of bites to humans or other animals. Tetanus toxoid vaccination is also recommended. Protocols usually involve a series of 2–3 injections followed by boosters every 5–10 years or following traumatic injuries. Other vaccines developed for humans (e.g., measles, influenza, polio, etc.) have also been used safely in some primate species. Killed or inactivated vaccines should be used when possible.
Serologic screening tests for a wide variety of viral diseases are available through commercial primate diagnostic labs. Taxa-specific panels are often used as routine screening tests to detect subclinical diseases of concern.
Fresh fecal samples should be evaluated with a direct smear as well as with flotation or centrifugation techniques to screen for protozoa and parasite ova. Special staining may be required to identify and speciate protozoa. Giardia and Cryptosporidium ELISAs can be used as a more sensitive screen for those pathogens. Stool cultures for enteric bacterial pathogens are often part of an annual health screen. Special media and techniques may be required for some bacterial pathogens. Electron microscopy can be performed to check for the presence of viruses in cases of diarrhea of unknown etiology.
Surgical techniques are options for permanent contraception. Ovariohysterectomy and castration are not usually recommended in healthy individuals due to hormonal changes that affect behavior and social status. Tubal ligation and vasectomy are more appropriate surgical techniques that maintain hormonal effects. Progestagens (e.g., melengestrol acetate implants, medroxyprogesterone injection, etc.) are the most commonly used reversible contraception options. Gn-RH agonists (e.g., deslorelin) have also been used in primates of both sexes.
Quarantine of all newly acquired primates is highly recommended. Quarantined individuals should be housed in isolation with PPE and procedures in place to prevent spread of disease. A minimum of 30 days is recommended for animals with known medical histories, while 90 days or longer should be considered in individuals with unknown medical histories. A thorough physical exam and all preventative medicine diagnostic screening should be performed during the quarantine period.
Enrichment is the process of providing environmental stimuli to an animal to promote natural behaviors and reduce unwanted behaviors. Enrichment is an important part of primate husbandry due to their high intelligence, and is required by the USDA's Animal Welfare Act. Enrichment can include manipulative items, changes in diet presentation, training programs, changes to the enclosure, and interactions with conspecifics.
Tuberculosis in primates is usually caused by Mycobacterium tuberculosis, and occasionally M. bovis. The disease has a slow, chronic progression with lethargy, anorexia, and respiratory signs. Thoracic lymphadenopathy is the most common radiographic lesion, unlike humans who exhibit pulmonary granulomas. Quarantine and TB surveillance are key to prevention, as treatment is challenging and controversial.
Common enteric pathogens include Yersinia pseudotuberculosis, Y. enterocolitica, Shigella spp., Salmonella spp., Escherichia coli, and Campylobacter jejuni. All can present with diarrhea or other GI signs. Some can cause bloody diarrhea and extraintestinal signs. Treatment is supportive.
Other Bacterial Diseases
Clostridium tetani can cause tetanus and is associated with contaminated wounds. Prevention is with vaccination. Listeria monocytogenes is associated with contaminated food and causes abortion or sepsis/meningoencephalitis of newborns. Streptococcus pneumoniae can be spread through the aerosol route and can cause pneumonia or meningitis. S. zooepidemicus has been associated with lymphadenitis in callitrichids that had access to contaminated horse meat.
Macacine herpesvirus 1 (McHV-1; aka herpes B) causes severe fatal disease in most primates and humans, but minimal lesions in the natural host, macaques. PPE and handling protocols are essential in preventing this serious disease when working with macaques. Other herpesviruses have similar behavior where they are relatively harmless in natural hosts, but potentially fatal in other closely related species. Saimiriine herpesvirus 1 (SaHV-1) found in squirrel monkeys is lethal to owl monkeys and callitrichids. Ateline herpesvirus 1 (AtHV-1) found in spider monkeys is also lethal to callitrichids. Herpes simplex virus (HSV-1, HSV-2), the cause of cold sores in people, has been shown to be lethal to callitrichids, gibbons, and great apes.
Retroviruses such as Simian Immunodeficiency Virus (SIV), Simian Retrovirus (SRV), and Simian T-cell Lymphotropic Virus (STLV-1) are associated with immunosuppression and lymphoproliferative disorders. Evolution of human pathogens from these viruses (e.g., HIV, HTLV) emphasizes the importance of PPE and zoonotic disease control. Foamyviruses are another retrovirus common to many primates that have exhibited transmission to humans. Clinical signs have not been reported from this virus in people or primates.
Paramyxoviruses and Orthomyxoviruses (e.g., Parainfluenza, Influenza) can cause respiratory disease in primates. Severe disease can result when combined with other pathogens. Measles can be acquired from humans and may cause facial erythema/edema, a maculopapular rash, and fever. Vaccination for both measles and influenza have been performed in some primates. Encephalomyocarditis Virus is a Picornavirus found in the Gulf states and is carried by rodent vectors. It can cause sudden death in primates and other species. Lymphocytic Choriomeningitis Virus is also associated with rodents and causes liver and neurologic signs in callitrichids. Hepatitis A is a Picornavirus that may be asymptomatic or cause anorexia and diarrhea in all primate groups following fecal-oral transmission. Hepatitis B is a blood-borne Orthohepadnavirus that might be asymptomatic in gibbons and great apes. Primates are susceptible to rabies, which may be prevented with killed vaccines. A thorough reference on primate virology is available.7
Strongyloides stercoralis, S. fuelleborni, and S. cebus can cause pruritis, dyspnea, or hemorrhagic diarrhea or even death in some primates. The pinworms Enterobius vermicularis and others colonize the cecum/colon and may by asymptomatic or cause perianal itching. The whipworm Trichuris trichiura colonizes the cecum/colon and may cause mucoid/watery diarrhea. The nodular worms Oesophagostomum spp. affect apes and OWPs causing submucosal nodules in the colon or cecum. The spirurid Gonglyonema pulchrum affects the mouth and upper GI tract of NWPs and is transmitted through ingestion of cockroaches.
Entameba histolytica can colonize the large intestine and cause ulcerative colitis and extraintestinal lesions, but should not be confused with commensal protozoa such as Entameba coli and others. Balantidium coli is often nonpathogenic, but can cause ulcerative colitis, especially during times of stress. Both Entameba and Balantidium can be treated with metronidazole or paromomycin. Giardia intestinalis infections may be asymptomatic or cause mucoid diarrhea. ELISA testing can help detect infections, which can be treated with quinacrine, metronidazole, or tinidazole. Toxoplasma gondii is a systemic protozoal disease associated with cat feces or consumption of intermediate hosts. Toxoplasmosis causes more severe disease in lemurs and NWPs. Treatment with atovaquone shows some promise. Encephalitozoon cuniculi can mimic toxoplasmosis in NWPs.
Primates usually give birth at night with the fetus presenting head first. Breech presentation is the most common cause of dystocia, although diabetes and pelvic malformations can also be a cause. Endometriosis is the presence of hormonally responsive endometrium in an abnormal location and is common in primates. Treatment is ovariohysterectomy. Leiomyomas are benign smooth muscle tumors of the uterus that can affect reproduction or cause space-occupying clinical signs.
Diabetes is reported in primates and is most often Type 2 caused by amyloid deposition in islets of the pancreas. Obesity is a predisposing factor. Gestational diabetes also occurs and can lead to fetal macrosomia. Obesity is also common and often caused by improper diet and inadequate exercise. Obesity is associated with insulin resistance, endocrinopathies, adipokine changes, osteoarthritis, and heart disease.
Renal disease from glomerulonephritis (caused by chronic antigen-antibody formation) or from interstitial nephritis can lead to chronic renal failure. Cardiac diseases reported in primates include fibrosing cardiomyopathy, dissecting aortic aneurysms, and atherosclerosis. Cardiomyopathies are the leading cause of death for all captive great ape species.6 Osteoarthritis/spondylosis is common in older primates, and can be treated with traditional regimens.1
Like humans, primates are unable to synthesize vitamin C and therefore require it in their diet. Signs of deficiency (scurvy) include gingival hemorrhage, periodontal bone resorption, epiphyseal fractures, and anemia. NWPs have a higher vitamin D requirement than OWPs and cannot convert vitamin D2 to D3. Exposure to UV light and a proper diet is important in these species.
Primates can get many neoplasms, but those reported with increased incidence include colonic adenocarcinomas in cottontop tamarins, myelolipomas in Goeldi's monkeys, and lymphoproliferative disorders in individuals infected with SIV or STLV-1.
Periodontal disease and tooth root abscesses are common and can be prevented with proper diet and routine dental care. Dental fractures often require endodontic therapy or extraction. Canine teeth should not be altered for non-medical reasons.
Traumatic injuries are common in primates and should be handled with routine treatments except that sutures should all be buried to prevent picking. Tail tips may need to be amputated if severely traumatized. Abscesses often are the result of focal punctures caused by bite wounds.
Amyloidosis (type AA) is common in primates and often secondary to chronic inflammatory processes. The disease may manifest as hepatosplenomegaly, chronic renal failure, chronic weight loss, or diarrhea. Treatment is aimed at the underlying condition.
Behavioral disorders such as stereotypic behavior and self-injurious behavior (e.g., alopecia, trauma) can be problematic in primates. Environmental modifications and behavioral modifications may be needed to get to the root of the problem. If self-injurious behavior is severe, neuroleptics or SSRIs may be necessary.
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2. Bennett BT, Abee CR, Henrickson R, eds. Nonhuman Primates in Biomedical Research: Diseases. Academic Press, San Diego, California. 1998.
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6. McManamon R, Lowenstine L. Cardiovascular disease in great apes. In: Fowler ME, Miller RE, eds. Fowler's Zoo and Wild Animal Medicine: Current Therapy, Volume 7. Elsevier, St. Louis, Missouri. 2012:408–415.
7. Voevodin AF, Marx PA, eds. 2009. Simian Virology. Wiley-Blackwell, Ames, Iowa.