A disease characterized by a mild to severe nasal discharge has been seen for many years in captive tortoises in Europe, England, and the United States. Although a complete list of the number of tortoise species known to develop this disease is unavailable, it would be fair to say that until proven otherwise, all species of tortoises should be considered susceptible. In England this disease is commonly seen in Greek (Testudo graeca) and Hermann's (Testudo hermanni) tortoises.1
Attempts at demonstrating or incriminating a causal agent have been unsuccessful. Because of negative findings and the failure to incriminate a specific bacteria, a virus has been considered a possible cause of this disease.2
At Veterinary Medical Teaching Hospital, University of Florida, species of tortoises presented with nasal discharge include Greek tortoises, leopard tortoises (Geochelone pardalis), radiated tortoises (Geochelone radiata), Indian star tortoises (Geochelone elegans), and gopher tortoises (Gopherus polyphemus). This disease has also been commonly seen in captive desert tortoises (Xerobates (Gopherus) agassizii).3
In studies conducted on captive desert tortoises a bacterial organism, Pasturella testudinis, has been isolated and incriminated as a possible cause of this disease.4
However P. testudinis has also been isolated from healthy tortoises and the significance of this organism remains unknown.
Respiratory disease in wild tortoises
In 1988, desert tortoises at the Desert Tortoise Natural Area, Kern County, California were seen with clinical signs of illness similar to that of captive desert tortoises. Signs included a mucopurulent discharge from the nares, puffy eyelids, eyes recessed into the orbits, and dullness to the skin and scutes. Based upon these clinical signs, the term Upper Respiratory Disease Syndrome (URDS) was used to characterize this syndrome.
In surveys of the Desert Tortoise Natural Area in 1989 and 1990 it became clear that many desert tortoises were ill with this disease and shells of many tortoises indicated that there was a major die-off. Other surveys indicated that free-ranging desert tortoises with URDS also were seen in other areas in the Western Mojave Desert, around Las Vegas, Nevada, the Beaver Dam Slope of Utah/Arizona, and sporadically in low numbers in the Sonoran Desert of Arizona.
In May 1989, with a contract from the U.S. Bureau of Land Management, we initiated studies on desert tortoises ill with URDS in an attempt to elucidate the responsible pathogens. In the course of these studies the pathology of this disease was better understood and findings indicated that the upper respiratory tract was the major site of involvement. Based on these findings the disease was found to be a chronic upper respiratory tract disease and the acronym URDS was used. Today, URTD more appropriately designates this illness and should replace URDS.
The search for the cause
Microbiologic investigations with URTD failed to incriminate a virus as a potential causal agent. Pasturella testudinis was isolated from most of the ill animals examined and a previously unidentified Mycoplasma was also isolated from ill tortoises. Electron microscopy studies confirmed the presence of Mycoplasma on the surface membranes of the upper respiratory tract of desert tortoises ill with URTD. Based upon what we know in birds and mammals, P. testudinis and Mycoplasma, either individually or in combination could be responsible for this disease.