Epidemiology of Infectious and Other Diseases in Agassiz’s Desert Tortoise

Science Center Objects

Agassiz’s Desert Tortoise (Gopherus agassizii) was listed as threatened in 1990 under the Endangered Species Act. WERC’s Dr. Kristin Berry leads studies on the cause of diseases in populations of Agassiz’s Desert Tortoise across the Mojave and western Sonoran deserts in southern California.

What causes infectious diseases and other illnesses in desert tortoises? The summaries below offer insight into WERC projects that improve our ability to prevent the spread of infectious disease, to study the effects of upper respiratory tract disease on tortoise mortality, determine the frequency of herpesvirus infections in tortoise populations, and identify toxicants and other factors that cause shell diseases and other illnesses.

Desert Tortoise Mortality

Dr. Kristin Berry studies the causes of poor health and mortality in Agassiz’s desert tortoises (Gopherus agassizii) in the Mojave Desert. The U.S. Department of Defense, U.S. Bureau of Land Management, National Park Service, and California Dept. of Fish and Wildlife are responsible for managing key habitat for this threatened species. To provide these agencies with the information they need, Dr. Berry is defining the characteristics of diseased and healthy tissues and identifying the pathogens (viruses, bacteria, etc.) and toxicants (mercury, lead, arsenic, etc.) that affect tortoise health. She also collaborates with geochemists and geologists to understand how toxicants build up in tortoises’ tissues, whether from breathing particles, direct contact, or ingestion of plants, soil, or trash.


Identifying Causes of Shell Disease in Desert Tortoises

After the listing of Agassiz’s desert tortoise as a threatened species, several populations have continued to decline. Shell disease is associated with elevated mortality in tortoises living in the Colorado Desert and in the eastern Mojave Desert. WERC’s Dr. Kristin Berry leads efforts to identify and understand the causes of shell disease in populations of desert tortoises in California. Study results will support the U.S. Bureau of Land Management and U.S. Fish and Wildlife Service in management actions to stabilize and improve the trends in desert tortoise populations, with the ultimate goal of facilitating recovery of the species. Dr. Berry’s project also delivers important information to the USGS Mineral Resources Program and can assist resource managers in making wise land-use decisions in the urban-wildland interface, as well as in wildlands.


Upper Respiratory Tract Disease in Agassiz’s Desert Tortoise

Dr. Berry leads long-term projects on the epidemiology of upper respiratory tract disease (URTD) in the California deserts. Specifically, she studies distribution and chronicity of URTD caused by two species of bacteria: Mycoplasma agassizii and M. testudineum. Her research supports efforts by the U.S. Bureau of Land Management, Fish and Wildlife Service, and Department of Defense to detect disease and trauma in Agassiz’s Desert Tortoise early, rapidly assess their health, and recover their populations.