28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

NSF Project on "URTD and the Environmentally-Threatened Gopher Tortoise"

Mary B. Brown¹, Paul A. Klein², Madan Oli³, Earl McCoy⁴, Henry Mushinsky⁴, Lori Wendland¹, Daniel Brown¹ and Joan Berish⁵
Department of Pathobiology, College of Veterinary Medicine,¹ Department of Pathology, Immunology and Laboratory Medicine, College of Medicine,² College of Wildlife Ecology and Conservation,³ University of Florida, Gainesville, Florida;
⁴Department of Biology, University of South Florida, Tampa, Florida; 
⁵Bureau of Wildlife Diversity and Conservation, Florida Fish and Wildlife Conservation Commission, Gainesville, Florida.

In a unique interdisciplinary program, the National Institutes of Health, the National Science Foundation, and the U.S. Geological Survey combined to sponsor a program initiative "Ecology of Infection Diseases" to elucidate the underlying mechanisms that govern the relationships between anthropogenic environmental changes and the transmission dynamics of infectious diseases. Investigators at the University of Florida, the University of South Florida, and Florida Fish and Wildlife Conservation Commission were awarded a five-year grant under this program. The project is described below.

Infectious diseases are an ever-present risk to wildlife, particularly during situations in which animals are removed from their natural habitat for captive breeding programs or during conditions of stress such as release into new habitats, translocation, ecosystem perturbation, and encroachment on their habitats by urbanization. This is even more important when the species concerned is a keystone species such as the gopher tortoise that is critical to ecosystem health, maintenance of biological diversity of upland habitats, and survival of over 360 vertebrate and invertebrate species. Further, in a long-lived species that does not attain reproductive maturity for 10 to 20 years, a single catastrophic event such as a disease epidemic can result in devastating population losses from which the population may have difficulty in recovering.

Upper respiratory tract disease (URTD) is among the best, if not the best, characterized infectious disease in reptiles. The primary etiologic agent of URTD in both gopher and desert tortoises is Mycoplasma agassizii (4, 5). Serological and molecular diagnostic tests have been developed for the infectious agent, and these diagnostic tests have been applied to both wild and captive populations (1, 2, 3, 6, 8, 11, 12). Finally, the presence of specific antibody has been correlated with the presence of clinical signs and histopathological lesions (7, 8, 9, 10, 11). The next logical step, which is the focus of this project, will be to study the influence of URTD on wild tortoise populations. Our long-term goal is to understand the relationship between URTD and tortoise population dynamics and health, with special emphasis on the impact of anthropogenic effects such as relocation practices and habitat alteration on disease transmission. Our study will address the following hypotheses: 
1. Both natural and anthropogenic-induced population characteristics play a critical role in disease transmission and prevalence. 
2. Habitat factors such as quality, size, and fragmentation influence disease transmission. 
3. URTD has a negative impact on tortoise demographic characteristics, and therefore on the viability of tortoise populations.
4. Mycoplasma strains vary in virulence, and the strain of mycoplasma present in a given population will influence the severity and transmission of URTD. 
5. URTD remains clinically undetectable until a certain threshold (as quantified by seroprevalence) of infected individuals is reached. Beyond that critical threshold, disease spread is more rapid and host population declines may occur.

This research project represents a unique, multidisciplinary approach to understanding the relationship between URTD and the ecology and basic biology of the gopher tortoise. The research includes studies at the population, individual, physiological, cellular, and molecular levels. Causal and predictive models will be developed for the transmission of URTD within wild tortoise populations. The information gained will benefit the long-term survival of the gopher tortoise in its natural habitat by providing new data on the effect of URTD on threatened tortoise populations. URTD represents an intriguing model to study establishment, transmission, maintenance, and consequences of chronic infection within a population. Understanding the dynamics of disease spread in natural wildlife populations may provide valuable new insights into host: parasite: population interactions in this era of emerging infectious diseases.

Figure 1. Conceptual representation of the influence of anthropogenic, host, microbial and habitat factors on disease transmission and population demographics. Major effects on the response variables (disease transmission and population demographics) are depicted by large, shaded arrows. Interaction among forcing variables (anthropogenic, host, habitat and microbial factors) are depicted by small arrows; stippled arrows indicate indirect influences while solid arrows indicate direct influences.

Similar research funding opportunities for investigating the multi-factorial causes of morbidity and mortality in the desert tortoise exist. There are several keys to obtaining significant funding from sources such as the National Science Foundation and National Institutes of Health. First, interdisciplinary teams of scientists representing broad disciplines must be established. Secondly, the projects must be hypothesis driven and represent strong science with cutting edge technologies. Third, because the factors influencing morbidity and mortality are undoubtedly multi-factorial, individuals with a strong training in theoretical modeling should be part of the team. Fourth, publication track record is a major evaluation tool for NSF and NIH reviewers. Therefore, it is imperative that team members publish their studies in the strongest peer-reviewed journals available. Data that is not accessible through standard search engines will likely be lost to the scientific community at large. Finally, the NIH and NSF web sites provide a wealth of information as to specific programs that are available. Successful applications are those that present their research questions and projects within the framework of interest of the specific funding agency or program.

References

1. Berry, K. H. 1997. Demographic consequences of disease in two desert tortoise populations in California, USA. In Proceedings: conservation, restoration, and management of tortoises and turtles--an international conference. J. Van Ebbema, ed. Wildlife Conservation Society Turtle Recovery Program and the New York Turtle and Tortoise Society, New York, N.Y. p. 91-99.

2. Brown, M. B, K. H. Berry, I. M. Schumacher, K.A. Nagy, M. M. Christopher, and P.A. Klein. 1999. Seroepidemiology of upper respiratory tract disease in the desert tortoise in the western Mojave desert of California. J. Wildl. Dis. 35:716-727.

3. Brown, D. R., B. C. Crenshaw, G. S. McLaughlin, I. M. Schumacher, C. E. McKenna, P. A. Klein, E. R. Jacobson, and M. B. Brown. 1995. Taxonomy of the tortoise mycoplasmas Mycoplasma agassizii and Mycoplasma testudinis by 16S rRNA gene sequence comparisons. Int. J. Syst. Bacteriol. 45: 348-350. 

4. Brown, M. B., I. M. Schumacher, P. A. Klein, K. Harris, T. Correll, and E. R. Jacobson. 1994. Mycoplasma agassizii causes upper respiratory tract disease in the desert tortoise. Infect. Immun. 62: 4580-4586. 

5. Brown, M. B., G. S. McLaughlin, P.A. Klein, B.C. Crenshaw, I. M. Schumacher, D. R. Brown, and E.R. Jacobson. 1999. Upper respiratory tract disease in the gopher tortoise is caused by Mycoplasma agassizii. J. Clin. Microbio. 37(7): 2262-269.

6. Diemer Berish, J. E., L. D. Wendland, and C.A. Gates. 2000. Distribution and prevalence of upper respiratory tract disease in gopher tortoises in Florida. J. Herpetology 34(1): 5-12. 

7. Homer, B.L., K. H Berry, M. B. Brown, G. Ellis, and E.R. Jacobson. 1998. Pathology of diseases in wild desert tortoises from California. J. Wildl Dis 34(3): 508-523.

8. Jacobson, E. R., M. B. Brown, I. M. Schumacher, B. R. Collins, R. K. Harris, and P.A. Klein. 1995. Mycoplasmosis and the desert tortoise (Gopherus agassizii) in Las Vegas Valley, Nevada. Chel. Cons. Biol. 1: 280-284. 

9. McLaughlin G. S. 1997. Upper respiratory tract disease in gopher tortoises, Gopherus polyphemus: pathology, immune responses, transmission, and implications for conservation and management. Ph. D. Dissertation, University of Florida, Gainesville. 110 pp. 

10. McLaughlin G. S., E.R. Jacobson, D. R. Brown, C. E. McKenna, I. M. Schumacher, H. P. Adams, M. B. Brown, and P.A. Klein. 2000. Pathology of upper respiratory tract disease of gopher tortoises in Florida. J. Wildl. Dis. 36(2): 272-283. 

11. Schumacher, I. M., D. B. Hardenbrook, M. B. Brown, E. R. Jacobson, and P. A. Klein. 1997. Relationship between clinical signs of upper respiratory tract disease and antibodies to Mycoplasma agassizii in desert tortoises from Nevada. J. Wildl. Dis. 33:261-266. 

12. Schumacher, I. M., M. B. Brown, E. R. Jacobson, B. R. Collins, and P. A. Klein. 1993. Detection of antibodies to a pathogenic mycoplasma in desert tortoises (Gopherus agassizii) with upper respiratory tract disease. J. Clin. Microbiol. 31: 1454-1460.