The Desert Tortoise and
Upper Respiratory Tract Disease
by Elliot Jacobson, DVM, MS, PhD
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
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.
Still, predisposing factors such as poor nutrition (resulting from habitat degradation), drought, and release of captive desert tortoises ill with URTD into the wild are more than likely involved. This whole issue of problems resulting from release of ill pet desert tortoises needs to be publicized because this practice should not continue. Until we know more, it is safe to assume that captive ill tortoises can transmit this disease to both captive and free-ranging clinically healthy tortoises.
Until recently, no antibiotics or combination of antibiotics have been efficacious for treating tortoises ill with URTD. Believing that Mycoplasma and Pasturella may be the most important organisms in URTD, antibiotic therapy with a combination of 10 mg/kg of body weight doxycycline (UDL Laboratories, Inc., Rockford, Illinois), given orally once per day for 30 days and ceftiofur (Naxcel, Upjohn Co., Kalamazoo, Michigan), given as an intramuscular injection once per day for two weeks, was considered the therapy of choice.
Dr. Walter Rosskopf, a veterinarian in private practice in Los Angeles, California, has reported success with this combination (personal communication). An alternative antibiotic which also appears to be efficacious is injectable enrofloxacin (Baytril, Mobay Corp., Shawnee, Kansas) at 8 mg/kg once per day for two weeks. Dr. Rosskopf also uses a daily nasal flush consisting of a combination of: 49.5 cc saline; 0.25 cc enrofloxacin; and 0.25 cc of tylosin (Elanco Co., Lily Corp., Indianapolis, Indiana). A small quantity (up to 0.5 cc) of this combination can be flushed up both nares of the affected tortoise utilizing a syringe and attached catheter of appropriate diameter. This should be continued for several weeks (at least until the rhinitis has abated). It is important to maintain tortoises at an optimum environmental temperature during the course of treatment.
Results of clinical trials with these new drugs and drug combinations for treating tortoises ill with URTD are extremely promising for captive tortoises. Unfortunately the situation for ill free-ranging tortoises is not as promising. Since this disease more than likely is multifactorial, schemes for managing URTD in free-ranging populations are going to be difficult to develop and implement. Tortoise hobbyists can make a major contribution by getting the word out that captive tortoises should not be released back into the wild. More than likely this practice has contributed to the spread of URTD in wild populations of desert tortoises.
1 Lawrence, K. & Needham, J. R. (1985) Rhinitis in long term captive Mediterranean tortoises Testudo graeca and T. hermanni). Veterinary Record 117: 662-664. 2 Jackson, O. F. & Needham, J. R. (1983) Rhinitis and virus antibody titers in chelonians. Journal of Small Animal Practice 24: 31-36. 3 Snipes, K. P., Biberstein, E. L. & Fowler, M.E. (1980) A Pasturella sp. associated with respiratory disease in
captive desert tortoises. Journal of American Veterinary Medical Association 177: 804-807. 4 Snipes, K. P. & Biberstein, E. L. (1982) Pasturella testudinis sp. nov.: a parasite of desert tortoises. International Journal of Systematic Bacteriology 32: 210-210.
Article reprinted with permission from the Desert Tortoise Preserve Committee, Inc.