Abstract

A retrospective study of morbidity and mortality of two-toed sloths (Choloepus didactylus and Choloepus hoffmanni) was conducted to elucidate medical problems diagnosed in captivity in North America. Eighteen out of 39 institutions responded to a request for medical records with a total of 101 animals represented. Findings were tabulated by organ system and divided into age groups. Major causes of morbidity in all groups included parasitemia, dental disease, and trauma. End-stage renal disease accounted for the majority of deaths. Phlebotomy sites included the cephalic, superficial antecubital, jugular, and femoral veins. Multiple anesthetic protocols were described with varying degrees of success.

Introduction

Sloths belong to the order Edentata, suborder Xenarthra, family Bradypodidae. This family contains two genera: Choloepus (the two-toed sloth) and Bradypus (the three-toed sloth). Species differ in anatomy, physiology, behavior, and habits. The term “sloth” applies to Choloepus in this paper. Choloepus didactylus is found in Guyana, northern Brazil, eastern Colombia, and eastern Venezuela. Choloepus hoffmanni is found from Nicaragua through Central America into Panama and then southward into Columbia, Venezuela, Guiana, Ecuador, Peru, Brazil, and Bolivia. Both species are found at the tops of tall trees in tropical rain forests, mixed deciduous forests, and secondary growth forests. They thrive in the high humidity found in the vicinity of rivers. Sloths are almost strictly arboreal but are good swimmers. They do not ambulate well on land.

C. didactylus usually has seven (range: six to eight) vertebrae, while C. hoffmanni usually has six (range: five to six). Sloths have limbs vascularized by rete mirable and an elongated thorax (21–25 pairs of ribs). They can withstand 10–40 minutes of apnea, but do not possess a specific “diving reflex.” Heart rate ranges from 70–130 beats/minute, with a respiratory rate of 13–14 breaths/minute. Mean body temperature is 34.4°C (94°F). Sloths are heterothermic and unable to shiver, but pant and do have sweat glands.⁵ Their thermoneutral zone is above 25°C (77°F), but critical ambient temperatures are from 12°C (53°F) to 30°C (86°F); sunshine can increase body temperature up to a lethal level.¹⁰ Sloths do well in enclosures that range from 24–29.5°C (75–85°F) with humidity at 60–70% (minimum 40%).^3,4 Sloths weigh from 2.7–8.1 kg, but the gastrointestinal contents and urine can account for up to 20–30% of their body weight. Sloths generally defecate and urinate at the same time with a frequency of once every three to eight days. The bladder of an adult sloth can hold up to 1.5 L of urine. Sloths have a low metabolic rate, which is attributed to low thyroid function not hypothyroidism.⁵ In captivity they rest or sleep approximately 20 hours/day. Free-ranging sloths remain active through most of the night resulting in approximately 11 hours of activity/day.⁸ Sloths have one set of teeth their entire life; five upper and four lower. The teeth consist of dentine and vasodentine and are surrounded by cement. There is no enamel. Sloths have a ruminant-like stomach with three compartments. In the wild they eat a variety of plant material including buds, leaves, flowers, fruit, twig tips, and young stems. Animal material may also be consumed when available,⁸ although no documentation was found of this in wild sloths. Meat-based products are added to captive diets because sloths consume it readily when offered.⁵ They eat better when their food is diced as opposed to chunked or sliced.⁸ Vitamin K deficiency has been noted in other xenarthrans and has been added prophylactically to some diets. The sex of sloths can be difficult to determine, as the penis cannot always be expressed, and the testis are intra-abdominal. The opening at the genital protuberance appears more slit-like in the female than the male. Age in captivity can reach over 20 years and has gone beyond 30 years in a few instances.

Materials and Methods

Institutions housing two-toed sloths in North America were contacted and medical records requested for all deceased, transferred, and living animals at their institutions. Eighteen institutions responded with 101 animals represented. Some medical records contained very limited medical information but were included for completeness. Findings were tabulated by organ system and divided into age groups. Divisions include neonates <four weeks, four weeks to four years, four to 10 years, 10 to 15 years, 15+ years, and age unspecified. Disease processes were not separated by species because correct speciation of all animals was not known.

Morbidity

• Neonates <four weeks (five events)
  • Integument (20%): tropical rat mite
  • Trauma (20%): laceration
  • Gastrointestinal (20%): constipation
  • Misc. (40%): two were hand-reared (poor suckling, maternal neglect)
• Four weeks to four years (39 events)
  • Respiratory system (15%): nasal discharge, either mucoid or mucopurulent
  • Gastrointestinal ailments (38%): stomatitis, intestinal parasites, constipation, enteritis
  • Musculoskeletal (20%): dislocation of the carpus/metacarpus, osteosclerosis, bite or fight wounds, traumatic compression at L2–L3
  • Urinary tract (2.5%): urethritis
  • Integument (20%): burns, alopecia, ulcerative dermatitis, superficial abrasions, decubital sores, cutaneous abscess, pruritis with seborrhea sicca
  • Ocular (2.5%): bilateral conjunctivitis
• Four to 10 years old (56 events)
  • Respiratory (5.4%): nasal discharge
  • Gastrointestinal (18%): intestinal parasites, abdominal and umbilical hernia, dental tartar, dead tooth, enteritis
  • Musculoskeletal (47%): bite or fight wounds, porcupine quills in the mouth, torn/broken nails
  • Urinary (2%): cystitis
  • Reproductive (10%): serosanguinous vaginal discharge, aborted fetus
  • Integument (10%): abrasions, cutaneous abscesses, dermatosis, decubital sores, ulcerative dermatitis
  • Other (7.3%) heat stroke/stress.
• Ten to 15 years old (58 events)
  • Respiratory (3%): nasal discharge
  • Gastrointestinal (39%): dental problems, lingual ulcerations, mycotic glossitis
  • Musculoskeletal (22%): fight or bite wounds, fall, broken nails, puncture wound
  • Urinary (5%): renal calculi, pyelonephritis, urinary tract infection.
  • Ocular (3%): corneal scratch, corneal scar
    
  • Reproductive (9%): mastitis, abortion in second trimester, mid-term abortion
  • Cardiovascular (3%): mineralized descending aorta, first-degree AV block
  • Integument (16%): ectoparasites, abrasions, moist dermatitis, infected puncture wounds, burns, periocular alopecia, generalized alopecia and pruritis
• Fifteen+ years old (57 events)
  • Respiratory (10%): nasal discharge, thoracic mass
  • Gastrointestinal (30%): dental problems, intestinal parasites, oral candidiasis, protozoal enteritis
  • Musculoskeletal (12%): nails ripped off, deformed nail, fight or bite wounds
    
  • Urinary (14%): cystitis, renal calculi, cystic calculi
  • Ocular (12%): cataracts, mucopurulent discharge, foreign body, corneal ulcer, mucoid discharge
  • Reproductive (9%): minimal multifocal fibrinopurulent placentitis, early term abortion, penile discharge
    
  • Cardiovascular (2%): possible calcification of aorta
    
  • Integument (11%): abrasions, external parasites, interdigital dermatitis, aural hyperkeratosis, Bowenoid carcinoma in situ, mucocutaneous ulcers, ulcerative epidermitis, lymphoplasmacytic superficial dermatitis
• Age unspecified (24 events)
  • Respiratory (17%): nasal discharge.
  • Gastrointestinal (29%): intestinal parasites, mycotic stomatitis
  • Musculoskeletal (12.5%): broken nails accounted for all of these incidences
  • Ocular (8%): conjunctivitis, mucopurulent discharge
  • Integument (33%): cutaneous cysts, burns, moist dermatitis, periorbital dermatitis, laceration

Mortality

• Neonates (nine sloths)
  • Aborted fetus’ (22%): early term and second trimester
  • Stillborn (22%): amniotic aspiration, acute fetal distress syndrome
  • Respiratory (11%): drowning
  • Musculoskeletal (11%): perinatal trauma
  • Unknown (33%): no necropsy performed, passive congestion of all organs with no specific disease process identified, possible abortion
• Four weeks to four years (eight sloths)
  • Respiratory (25%): drowning, aspergillosis
  • Cardiovascular (12.5%): systemic septicemia
  • Unknown (62.5%): no necropsy performed
• Four to 10 years old (two sloths)
  • Systemic septicemia; no necropsy performed
• Ten to 15 years old (four sloths)
  • Gastrointestinal (25%): gastric impaction
  • Cardiovascular (25%): terminal septicemia
  • Urinary (50%): end stage renal disease, tubulointerstitial nephritis
• Fifteen+ years old (four sloths)
  • Gastrointestinal (25%): perforating ulcer in fourth chamber of stomach
  • Unknown (25%): euthanatized due to old age, “many age related problems” at necropsy
  • Urinary (25%): renal disease
  • Mixed (25%): end stage kidneys (cystic) with severe diffuse histiocytic to purulent necrotizing bronchopneumonia
• Age unspecified (nine sloths)
  • Gastrointestinal (11%): gastric ulceration
  • Cardiovascular (11%): cardiac valvular disease
  • Unknown (33%): no necropsies performed
  • Urinary (45%): end stage kidney disease, carcinoma of bladder, transitional cell carcinoma of the bladder

Discussion

Parturition was noted in all age groups over four years of age. Overgrown nails were seen in all age groups except neonates. Abnormal nail growth was not uncommon and was associated with osteosclerosis of the distal interphalangeal joints in one case. Nasal discharge was not always associated with a specific etiology, and many of the organisms cultured were considered commensals. Increased humidity improved or resolved clinical signs in many cases. In the sloths that died of pneumonia, nasal discharge was only occasionally seen premortem.² Fungal organisms were seen on tracheal lavage of one sloth with a thoracic mass. Madurella and Penicillium were cultured and the animal responded to anti-fungal therapy.

Candida was present in several cases of glossitis/stomatitis. The diagnosis was based on cytologic exam of oral lesions. E. coli, Aeromonas, Enterobacter, and Salmonella have been cultured from feces of animals with enteritis, but their contribution to the disease process is unknown. Salmonella was also cultured from the gastrointestinal tract of animals without clinical disease and has been reported in asymptomatic free-ranging animals.⁶ Intestinal parasites included strongyles, hookworms, flukes, ciliates, flagellates, tapeworms, strongyloides, nematodes, coccidia, and trematodes. Dental diseases included tartar, dead teeth, points on cheek teeth, overgrown canines, mild gingivitis, fractured teeth, periodontal disease, gingival hyperplasia, malocclusion, excess wear, and abscessed teeth. More dental disease was reported in the older animals, especially points that were causing oral ulcerations/lacerations.

Bite or fight wounds occurred frequently, and slow introduction of sloths in enclosures large enough to provide a territory for each animal is recommended. Fighting was alleviated in some cases when more food pans were added to the enclosure, with hanging branches placed close enough to allow animals to eat comfortably. Over half of the bite wounds reported became infected. Burns from hot water pipes in the enclosure were common. Torn or broken nails were suspected to occur from entrapment of nails in portions of the exhibit, especially air or heating vents.

Urinary tract infections were reported frequently. While the cause the infections was not always known, E. coli was cultured in a few instances, and Streptococcus Group D was isolated from an animal with pyelonephritis. Pyuria did not always accompany bacteriuria. Flagellates and fungi were identified in urine sediment collected by cystocentesis. These conditions were not treated, and their clinical significance was not determined. Renal calculi were diagnosed radiographically multiple times. Cystic calculi were associated with rectal prolapse in one animal.⁹ Calculi were composed of calcium, magnesium, ammonium, and phosphorus in one sloth, while another animal had crystals containing magnesium phosphate hydrate, carbonate apatite, and protein.⁹ Previously urinalysis values reported for sloths differ from those recorded in the medical records reviewed.⁷ Isosthenuria was noted in clinically normal animals. Water deprivation tests are not recommended in this species, as death occurred in some of the sloths when attempted.⁵

Kidney disease was a frequent cause of death. Blood values obtained prior to death in animals which died from renal failure did not consistently show azotemia. The death from gastric impaction was secondary to interstitial nephritis and dystrophic calcification of the stomach. Gastric mucosal mineralization was identified in another animal that died with end stage renal disease. Mineralization of the descending aorta was visualized radiographically in more than one animal.

Phlebotomy sites included the superficial antebrachial or the cephalic vein, the jugular vein using ultrasonic location in some cases, the femoral vein using doppler detection,¹ and a quicked nail. Cardiocentesis and the dorsal vertebral vein have been reported as phlebotomy sites.^3,4 The dorsal vertebral vein is a 10 mm diameter vein that lies extradurally to the right of the spinal cord in the dorsal region, with nerve roots passing dorsal to it.⁵ Heparin and EDTA were utilized as anticoagulants, but hematologic profile studies use EDTA.^1,11,12

Various anesthetic protocols have been utilized including isoflurane for induction and maintenance; ketamine 2–6 mg/kg for sedation; ketamine plus halothane, nitrous oxide and oxygen, and Telazol 2–6 mg/kg. During translocation of 202 wild sloths, four anesthetic protocols were evaluated,¹⁰ including acepromazine 0.1 mg/kg + ketamine 10 mg/kg; xylazine 1 mg/kg + ketamine 10 mg/kg; tiletamine + zolazepam 10 mg/kg combine; and medetomidine 0.04 mg/kg + ketamine 3 mg/kg. The two protocols recommended for 30–40 minute procedures (including minor surgeries) were medetomidine 0.04 mg/kg + ketamine 3 mg/kg or xylazine 1 mg/kg + ketamine 10 mg/kg.¹⁰ Atipamezole at five times the medetomidine dose is recommended for reversal. Intubation can be very difficult in sloths.

Although early reports recommended reduction in dosage and frequency of medication due to the large stomach and low metabolic rate,³ subsequent articles suggest this is not necessary. The injectable route may be preferable due to the unknown effect of oral medications on the forestomach and vice versa. Selection of oral medications should be guided by ruminant protocols, and the use of doxycycline or certain sulfa drugs is recommended.⁴

The clinical presentation of a sick sloth was similar in many cases and included weakness, dehydration, anorexia, and weight loss. Routine physical examination of sloths was not common. Animals were generally evaluated only when problems arose, which may have resulted in disease processes being missed if the clinical signs did not warrant evaluation of the animal under anesthesia. Routine health assessments of sloths under anesthesia is encouraged and should include whole body radiographs, blood collection for complete blood counts and serum chemistry evaluation, and cystocentesis for urinalysis.

Acknowledgments

I would like to thank the following institutions for submitting medical records: Alexandria Zoo, Brevard Zoo, Caldwell Zoo, Calgary Zoo, Cleveland Zoo, Columbus Zoo, Mesker Park Zoo, Milwaukee County Zoo, Montreal Zoo, National Zoo, Riverbanks Zoo, Reid Park Zoo, St. Louis Zoo, Toledo Zoo, Toronto Zoo, Tulsa Zoological Park, Valley Zoo, and the Zoo England Zoo.

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