Upper Respiratory Tract Disease (URTD) caused by the bacteria Mycoplasma agassizii (Brown et al., 1995), has been reported in many tortoise populations and is the suspected cause of some recent large scale die-offs in Florida. Outbreaks of URTD have been documented in captive and wild populations of the desert tortoise, Gopherus agassizii, and in the gopher tortoise, Gopherus polyphemus (Deimer-Berish et al., 2000). Two hypotheses may explain the presence of URTD in a tortoise population (Deimer-Berish et al., 2000). (1) M. agassizii may be a naturally occurring bacterium found in tortoises but can become pathogenic when a tortoise is stressed (caused by habitat fragmentation, diminished food resources, relocation, drought, captivity, etc.). (2) URTD may be introduced into a population when an already infected tortoise is moved to a new site (Deimer-Berish et al., 2000).
Symptoms of URTD include nasal and ocular discharge, conjunctivitis, palpebral edema (swollen eyelids), chitinous scarring of the shell, labored breathing, lethargy, anorexia and death (McLaughlin, 1997). An infected tortoise may show no outward symptoms and can spread the bacteria whenever it comes in contact with another tortoise. A tortoise may become re-infected once it has had the disease (McLaughlin, 1997).
In June of 2001 a project was initiated to assess the prevalence of URTD in the Wekiva Basin GEOpark in Orange, Seminole, Volusia, and Lake Counties. Included in the GEOpark are Wekiwa Springs State Park, Lower Wekiva River State Preserve, and Rock Springs Run State Reserve (RSRSR). Rock Springs (where the die-off occurred) is a 13, 710 acre Type I Wildlife Management Area. It is composed of a mixture of habitat types including sandhill, scrub, flatwood, hydric, mesic and xeric hammock, swamp and small, marshy ponds. However, the die-off occurred in wellmaintained sandhill. Prescribed burning is used to maintain the quality of the habitat, although drought conditions have limited this activity since 1998.
Upon visual survey of approximately 150 acres of sandhill at RSRSR, approximately 125 dead tortoises were found between August and December 2001. Three marked tortoises were among the dead. Dead tortoises were concentrated in a central area of approximately 100 acres. Most tortoises were found plastron side up and within 5 meters of their possible burrow. A large majority were intact and bleach white, suggesting that they had been there for some time (Dodd, 1995). This population was surveyed in May of 2000 and showed no signs of mortality at that time.
Visual surveys continued from August to November 2001 in an attempt to collect tortoises to be tested for URTD. Because few tortoises were found, it was necessary to switch to bucket trapping to obtain a sufficient sample size. After collection, standard morphometric data was recorded as well as any visually obvious symptoms of URTD. Samples were sent to the University of Florida to be tested using ELISA for exposure to M. agassizii. Of the 22 tortoises tested, 14 (64%) tested positive for exposure to URTD and two tortoises (9%) were suspected of having been exposed to URTD.
Although the exact cause of the die-off has not been determined, many factors are being considered. Local Florida Fish and Wildlife Conservation Commission staff has reported tortoises being dropped-off at RSRSR. This could introduce individuals with URTD and infect the existing population. Strain virulence, burn history and burrow humidity may also be factors.
The occurrence of large-scale die-offs and their association with URTD has become more common in Florida in recent years (Cindy Gates, pers. comm.). Loss of suitable habitat, illegal development practices, drought conditions and a well-intending but under informed public may be contributing factors to its prevalence. Determining the factors affecting the distribution of URTD within and among populations, its virulence and possible solutions warrant future investigation.
Brown, D.R., Crenshaw, B.C., McLaughlin, G.S., Schumacher, I.M., McKenna, C.E., Klein, P.A., Jacobson, E.R., Brown, M.B. 1995. Taxonomy of the tortoise mycoplasmas Mycoplasma agassizii and Mycoplasma testudinis by 16S rRNA gene sequence comparisons. Intl. J. of Syst. Bacteriol. 45:348-350.
Deimer-Berish, J.E., Wendland, L.D., and Gates, C.A. 2000. Distribution and Prevalence of Upper Respiratory Tract Disease in Gopher Tortoises in Florida. J. Herpetol. 34(1):5-12.
Dodd, C.K., Jr. 1995. Disarticulation of turtle shells in northcentral Florida: how long does a shell remain in the woods? Amer. Midl. Natur. 134:378-387.
McLaughlin, G.S. 1997. Upper respiratory tract disease in gopher tortoises, Gopherus polyphemus: pathology, immune responses, transmission, and implications for conservation and management. Unpubl. Ph.D. Dissertation, Univ. of Fla., Gainesville. 110pp.
Speake, D.W. 1981. The gopher tortoise burrow community. Pp. 44-47. In: Proceedings of the 2nd Annual Meeting of the Gopher Tortoise Council. Florida State Museum, Gainesville, FL.