Upper Respiratory Tract Disease
An Update - January 1998

by Grace S. McLaughlin

Over the past several years, the various members of our team (including Elliott Jacobson, Mary Brown, Paul Klein, Dan Brown, Isabella Schumacher, and myself) have presented numerous papers at the Desert Tortoise Council meetings on URTD, and have had several papers published in Journal of Wildlife Diseases, Chelonian Conservation and Biology, Infection and Immunity, and other journals.

We now know:

That URTD is caused by a Mycoplasma, and that Pasteurella testudinis by itself does not cause URTD, although it may be an opportunistic pathogen. Both herpesviruses, which have been isolated, and iridoviruses have been associated with respiratory disease in European tortoises. However, those diseases are also characterized by necrotic lesions in the mouth, and involvement of numerous organ systems.

Mycoplasmosis affects primarily the upper respiratory tract (nasal passages and nasal cavities). The mucosal and olfactory epithelia are damaged, possibly leading to loss of olfactory capabilities, and affecting various behaviors, such as foraging and social interaction.

Members of our team (Schumacher and Klein) developed a diagnostic blood test for antibodies against the Mycoplasma, and Dan Brown developed a polymerase chain reaction to detect mycoplasmal DNA. These are used in conjunction with culture techniques to determine a tortoise's status with respect to the mycoplasma.

We have found, in gopher tortoises, that the organism is spread by direct contact between tortoises, but that it does not appear to be transmitted through eggs. We also failed to detect transmission in a small environmental transmission study.

The disease is still very difficult to treat, and the long term prognosis is not good. Some tortoises (perhaps less than 20%) do seem to be able to clear the organism, but many harbor the bacteria within the nasal cavities for years, suffering recurrence of signs on an annual basis or when stressed.

Additional References:

1. Jacobson et al., 1991. Chronic upper respiratory tract disease of free-ranging desert tortoises, Xerobates agassizii. J. Wildlife Diseases 27: 296-316.
2. Schumacher et al., 1993. Detection of antibody to a pathogenic Mycoplasma in the desert tortoise (Gopherus agassizii). J. Clinical Microbiology 31: 1454-1460.
3. Brown et al., 1994. Mycoplasma agassizii causes upper respiratory tract disease in the desert tortoise. Infection and Immunity 62: 4580-4586.
4. Jacobson et al., 1995. Mycoplasmosis and the desert tortoise (Gopherus agassizii) in Las Vegas Valley, Nevada. Chelonian Conservation and Biology 1(4): 279-284.
5. Schumacher et al., 1997. Relationship between clinical signs of upper respiratory tract disease and antibodies to Mycoplasma agassizii in desert tortoises from Nevada. J. Wildlife Diseases 33(2): 261-266.
6. McLaughlin, G. S. 1997. Upper respiratory tract disease in gopher tortoises (Gopherus polyphemus): Pathology, secondary immune responses, transmission, and implications for conservation and management. Ph.D. Dissertation, University of Florida.

Grace McLaughlin was a Wildlife Ecologist/Epidemiologist in the Gopher Tortoise Upper Respiratory Tract Disease Project at Gainesville, Florida. She now lives and works in her native California.