Abstract

The aardvark (Orycteropus afer) is the only living representative in the order Tubulidentata, family Orcyteropodidae.² Tubulidentata means "tube teeth" and refers to the unique tubules found within the teeth. The genus name means "burrowing foot," another prominent feature of the aardvark. Aardvarks are completely nocturnal in the wild and feed primarily on ants and termites with their long sticky tongue. This hardy animal is currently found throughout much of sub-Saharan Africa wherever there is suitable habitat but once had a much larger geographic range reaching as far north as Europe.⁶

The aardvark is under CITES Appendix II, yet many authors have reported that aardvarks have decreased in numbers.^6,7 Their specialized diet may render them more vulnerable to habitat change caused by expanding human populations.⁸ In addition, they are also hunted for their meat, hide and claws.⁶ Today's North American population consists of 26 animals held at 10 institutions. Although aardvarks in zoos are living longer, reproduction remains challenging as evidenced by a captive population, which has been decreasing since 1994. Due to the dwindling numbers of captive aardvarks, preventative medicine and veterinary care are even more important for this small North American population.

Brookfield Zoo's (BFZ) first aardvark arrived in 1949. Since that time, 23 aardvarks have been cared for at the zoo; 4 were wild caught and 15 were captive born (11 at Brookfield). In captivity, their diet has primarily consisted of a gruel made from ground raw meat, eggs, milk, cereals, vitamin and mineral supplements. It is our experience at Brookfield that most of the aardvarks fed this diet go on to develop significant dental disease which has included caries formation, periodontal disease, and osteomyelitis. Attempts to approximate the animal's natural diet using dried locusts, flies, ant pupae, crickets and mealworms have been unsuccessful.^2,3

The aardvark's skull is elongated with a very small oral opening just large enough to allow its 30 cm tongue in and out. This unique anatomic feature makes routine dental examination and treatment especially difficult. The dental formula is I 0/0, C 0/0, P 2/2, M 3/3; additional vestigial premolars are sometimes present. In the adult, the teeth are located only in the posterior part of the jaw. The deciduous teeth are numerous, traversed by several parallel vertical canals, and do not erupt. Aardvark's teeth do not erupt simultaneously those nearest the front of the jaw develop first and often fall out as the animal ages. The cheek teeth are quite unusual, as they grow throughout life and are composed of hexagonal prisms of dentin surrounding a tubular pulp cavity. This pattern of growth gives the order its name, Tubulidentata (tubule-toothed).^1,6 The aardvark's teeth lack enamel, which may make them more susceptible to decay, and dental disease.

Previous reports discussing dental disease in aardvarks are few.^3-5 At Brookfield Zoo, dental disease seems more prevalent and difficult to treat in aardvarks compared to numerous other species. All three of the current adult aardvarks (two male, one female) at the zoo have been diagnosed and treated for dental disease. Both of the adult males required many months of treatment to resolve chronic mandibular osteomyelitis caused by complications associated with infected cheek teeth.

Aardvarks are darted with ketamine (Ketaset®, Fort Dodge Animal Health, Fort Dodge, IA, USA; 3 mg/kg) and medetomidine (Domitor®, Pfizer Animal Health, Exton, PA, USA; 0.03 mg/kg) IM, transported to the hospital, maintained on oxygen and supplemental isoflurane (Isoflo®, Abbot Laboratories, North Chicago, IL, USA) and intubated (size 10 long endotracheal tube) as necessary for oral surgery. Initial evaluation includes routine physical examination, oral examination (prior to intubation), hematologic and biochemical evaluation, as well as skull radiographs.

Aardvarks with dental disease have occasionally shown symptoms including difficulty chewing, ptyalism, anorexia and pain. Due to their small mouth opening and the caudal location of the cheek teeth, oblique skull radiographs appear to be the most sensitive method to detect dental disease in this species. Early signs of tooth abscessation include subtle pocket formation between the molars and the jaw. Significant erosive lesions may develop and teeth can even be completely detached but are not able to fall out because the mouth does not open far enough. Both maxillary and mandibular cheek teeth are affected; however, mandibular teeth are more commonly associated with osteomyelitis. The first clinical sign of osteomyelitis has been a slow-growing, firm, ventral, mandibular mass with or without a draining tract. Radiographs at this site may reveal abscessed teeth, bony lysis, periosteal proliferation, cyst formation, bony sequestra, fractures and retained tooth roots. Loose teeth can occasionally be removed with extra-long forceps (before endotracheal tube placement). More frequently, diseased teeth are sclerosed to surrounding bone and a buccal approach is required for extraction. Removal of retained tooth roots, bony sequestra, cyst ablation and debridement of proliferative lesions have required a ventral approach to the mandible. Curettage and debridement of mandibular lesions is accomplished with rongeurs and a round bur on a high­speed dental hand piece. Placement of ticarcillin-impregnated methylmethacrylate beads within the mandibular lesions appears to significantly aid in treatment of osteomyelitis.

Purulent malodorous material is routinely associated with the roots of affected teeth and bacteria isolated include Arcanobacterium sp., Bacteroides sp., Streptococcus sp., Staphylococcus sp., Enterococcus sp., Aerococcus sp. Arcanobacterium pyogenes-associated infections have been the most difficult to resolve and required long-term antibiotic therapy, dental extraction, and multiple surgeries to remove bony sequestra. Antibiotics used to treat aardvarks with dental disease include amoxicillin (±clavulanic acid), enrofloxacin, clindamycin, ceftiofur, metronidazole and tetracycline. Possible complications encountered during the treatment of dental disease in aardvarks include lingual swelling, hypoglossal nerve damage with subsequent tongue tip trauma necessitating amputation (secondary to attempts at retrograde pharyngeal intubation), and cheek wound dehiscence. The tongue begins to swell if it remains outside the oral cavity for even short periods of time and should be maintained within the mouth during dental procedures. Retrograde laryngeal intubation is not necessary as tracheal intubation can be done blindly with the animal in lateral recumbency with its head extended if at an appropriate depth of anesthesia. Auscult respirations and advance the endotracheal tube into the larynx at inspiration. Secure endotracheal tube to the mandible since the animals appear to be obligate nasal breathers.

Recently the aardvark diet has been changed at BFZ to eliminate the raw ground meat, which got caught in between teeth and likely contained high levels of bacteria. The diet now consists of ground dry cat food and leaf eater monkey biscuit mixed with water. It is our hope that the change in the aardvark's diet at Brookfield Zoo will help decrease the incidence of dental disease in this species.

Literature Cited

1.  Dieterich, R.A. 1986. Tubulindenta. In: M.E. Fowler (ed.) Zoo and Wild Animal Medicine. (2nd ed.). W.B. Saunders Co., Philadelphia. Pp. 595–597.

2.  Gierhahn, D. 2000. Aardvark, Orycteropus afer. North American Regional Studbook (3rd ed.). Chicago Zoological Society, Brookfield, IL USA.

3.  Goldman, G.A. 1986. A review of the management of the aardvark in captivity. Int Zoo Yb. 24/25:286–294.

4.  Gracis M. 1998. Root abscess in an aardvark (Orycteropus afer). J. Vet. Dent. 15:144.

5.  Karteoz, P. 1993. A Colour Atlas of Veterinary Dentistry and Oral Surgery. Wolfe Pub., London. Pp. 232–234.

6.  Nowak, R.M. 1999. Walker's Mammals of the World. (6th ed.). The Johns Hopkins Univ. Press., Baltimore. Pp. 1048–1049.

7.  Smithers, R.H.N. 1983. The Mammals of the Southern African Subregion. Pretoria: Univ. Pretoria.

8.  Van Aarde, R. J. 1985. Aardvark. In: D. MacDonald (ed.) The Encyclopedia of Mammals. New York. Pp. 466–467.