A severe case of malocclusion in a gray squirrel (Sciurus carolinensis) from Louisiana.
Malocclusion is a common form of oral disease found in rodents and rabbits (Hoff & Hoff 1996). This disease is the result of a misalignment of teeth and can affect dental eruption, occlusion, and attrition (Smith 1984; Van Der Merwe 1997). Rodents characteristically possess ever growing upper and lower incisors with enamel located only on the anterior side of the tooth. The gnawing behaviors of these animals quickly wear down the teeth and maintain the length of the incisors. Malocclusion can decrease wear on the teeth, resulting in incisors that grow to unusual lengths. This can impose several negative effects on the animal including difficulties in feeding, leading to starvation and death (Miles & Grigson 1990).On 28 February 2011, a free-ranging male gray squirrel (Sciurus carolinensis) with extreme malocclusion was harvested in a residential area of Sulphur, Louisiana (30.23[degrees]N, 93.36[degrees]W). Upon first examination, the left lower incisor was growing outside the oral cavity, up along the rostrum. Skinning further revealed that the top incisors possessed varying degrees of curling. The top right incisor had grown on the labial side of the cheekteeth (Fig. 1A). It had penetrated the masseter muscle near the PI and had completed a full turn. The top left incisor had grown between the rows of cheekteeth where it had curled up and penetrated the palatine (Fig. 1B). This tooth becomes slender and dark colored approximately 7 mm from the alveolus where it appears to be decaying. The lower incisors had grown up and to the left (Fig. 1C) and had come into contact with the left upper incisor where some tooth attrition had occurred on the mesial side of the lower right incisor and distal side of the top left incisor. To our knowledge, this is the first published case of malocclusion in a gray squirrel.
The cause of malocclusion in this individual may be the result from a lengthening in the mandible; a condition referred to as mandibular prognathism. This is a common cause of malocclusion in rabbits (Verstraete & Osofsky 2005). To determine if this condition existed, we averaged the length of the left mandible and maxilla of ten male gray squirrels in Louisiana and compared those to our individual. The average mandibular length of gray squirrels was 30.69 mm and average maxilla length was 17.78 mm, whereas our individual measured 32.53 mm and 17.32 mm, respectively. This suggests that the mandible of our individual was approximately 2 mm longer than the average, whereas the maxilla length showed little difference. This condition would cause abnormal occlusion ultimately leading to excessive incisor growth. Typically mandibular prognathism has a genetic origin (Fox & Crary 1971).
This individual weighed 375.31 g and the external measurements (mm) were: total length, 446; tail length, 209; hind foot length, 64; and ear length, 32. The weight and external measurements correspond to those of other gray squirrels previously collected in Louisiana (Lowery 1974). Difficulties in chewing as a result of malocclusion can lead to starvation and ultimately death for some rodent species (Miles & Grigson 1990; Hoff & Hoff 1996). However, examination of the gastrointestinal tract of this individual revealed an abundance of plant material suggesting that the individual was still able to ingest some food. No other skeletal anomalies were noted. This individual was deposited as a voucher specimen in the W.A.K Seale Vertebrate Museum, McNeese State University (Accession no. 9357).
Aside from the malocclusion, the only other abnormality observed in this specimen was a mild case of bilaterally symmetrical alopecia located in the shoulder regions (Figure ID). A possible cause of the hair loss could be a deficiency in diet due to the malocclusion (Lynch et al., 2012). Preferred foods of the gray squirrel include mast crop from multiple species of deciduous trees including oaks (Quercus) and hickories (Carya) that produce hard mast (Koprowski 1994). Examination of the GI tract showed extensive amounts of soft vegetative material with little to no hard mast. It is possible that the malocclusion caused the individual to diverge from a normal nutritious diet to one that was less nutritional, but more easily masticated. Other than the mild case of alopecia near each shoulder, the individual appeared to be in good health.
Literature Cited
Fox. R.R., & D. D. Crary. 1971. Mandibular prognathism in the rabbit: Genetic studies. J.Hered., 62(l):23-27.
Hoff, G.L., & D.M. Hoff. 1996. Dental anomalies in mammals. Pp. 203-211. in Noninfections diseases of wildlife (A. Fairbrother, L.N. Locke, and G.L. Hoff eds.), Manson Publishing. London, UK, xx+219 pp.
Koprowski, J.L. 1994. Sciurus carolinensis. Mammalian Species, 480: 1-9.
Lowery, G.H., Jr. 1974. The Mammals of Louisiana and Its Adjacent Waters. Louisiana State University Press, Baton Rouge, xx+565 pp.
Lynch, M., R. Kirkwood, R. Gray, D. Robson, G. Burton, L. Jones, R. Sinclair, &
J.P.Y. Arnould. 2012. Characterization and causal investigations of an alopecia syndrome in Australian fur seals (Arctocephalus pusillus doriferus). J. Mammal., 93(2):504-513.
Miles, A.E. W., & C. Grigson. 1990. Colyer's variation and diseases of the teeth of animals. Cambridge University Press, Cambridge, UK, xx+672 pp.
Smith, H.C. 1984. Malocclusion of Incisor Teeth in a Red Squirrel, Tamiasciurus hudsonicus. Can. Field Nat., 98(4):506-507.
Van Der Merwe, M. 1996. Maloclussion in an African rodent. Is it necessarily fatal? J. Zook. 243(4):689-694.
Verstraete, F. J. M., & A. Osofsky. 2005. Dentistry in pet rabbits. Compendium, 27(9):671-684.
JDH at: jhoffman@mcneese.edu
Sara E. Douga (1) and Justin D. Hoffman (2)
(1) Harold and Pearl Dripps Department of Agricultural Sciences (2) Department of Biological and Health Sciences McNeese State University, Lake Charles, LA 70609.
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| Title Annotation: | GENERAL NOTE |
|---|---|
| Author: | Douga, Sara E.; Hoffman, Justin D. |
| Publication: | The Texas Journal of Science |
| Article Type: | Report |
| Geographic Code: | 1USA |
| Date: | Feb 1, 2013 |
| Words: | 948 |
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