27th Annual Meeting and Symposium of the
Desert Tortoise Council, March 22-24, 2002
Abstracts

Clinical Implications of the Anatomy and Architecture of the Nasal Cavity of Tortoises

Elliott R. Jacobson
College of Veterinary Medicine, University of Florida, Gainesville, Florida 32610

The nasal cavity of chelonians occupies a large space cranial to the eyes and brain. This is a particularly prominent structure in tortoises. Cranially, the nasal cavity is continuous with the external nares. A heavily collagenous septum separates the cavity into both left and right portions. Caudally the nasal passageways are continuous with the internal nares (choanae). The nasal cavity varies in structure from cranial to rostral and at a histological level differs ventrally and dorsally. Ventrally the mucosa consists of both mucous and ciliated cells while dorsally it is primarily olfactory. There is a vary rapid transition from one type of epithelium to the other. The olfactory lobes of the brain send projections to the dorsal aspect of the cavity and only a small distance separates the brain from the nasal cavity.

In studying mycoplasmosis and herpesvirus infection in tortoises, the nasal cavity is the main site of involvement in the former and one of several sites of involvement in the later. In mycoplasmosis, the causative agent appears to first become established in a ventral recess that is continuous with the nasal passageway. Subsequently it spreads dorsally. In diagnosing both mycoplasmosis and herpesvirus infection, collection of samples (flushes) from the nasal cavity are routinely done in order to attempt isolation of these pathogens or identification of gene sequences using polymerase chain reaction. However collecting good representative samples of the cavity is often more difficult than first anticipated. Saline or a culture media is often flushed into and out of each nares or may be completely flushed through the nares and fluid escaping from the oral cavity of the animal collected as a "free catch". When the nasal cavity is examined, both by dissection and through specialized imaging such as the reconstruction of a three-dimensional CAT scan, the complexity of the cavity and the inherent difficulties of acquiring a representative sample from the entire cavity can be appreciated. Placing the tortoise in dorsal recumbency (carapace down) and the head tilted down, may allow the fluid used in the flush to have a better opportunity to come in contact with more dorsal regions of the cavity. Because the cavity may become occluded in chronically ill animals, trephaning both sides of the cavity and inserting catheters for subsequent flushing should be considered.