Removing Disease as a Roadblock to Desert Tortoise Conservation
Our mission in the Wildlife Disease Laboratories is to help remove disease as a roadblock to wildlife conservation. Our conservation programs face enough obstacles as it is – we don’t want disease to be one of them.
Unfortunately, disease problems have long been an obstacle to Mojave desert tortoise recovery. The problems were first identified over 20 years ago, when biologists recognized that population declines were occurring over large regions of the Mojave Desert. Many of the tortoises in these declining populations had evidence of upper respiratory tract disease. One of the main causes of this syndrome was determined to be a mycoplasma infection. Mycoplasmas are small bacteria that lack a cell wall and are generally transmitted by close contact.
It might seem surprising that a disease much like a severe cold in a person could cause death in a desert tortoise, but having an inflamed and congested nasal cavity not only results in excessive moisture loss in an already deadly dry environment, it makes it difficult for tortoises to find food and water by smell.
Although the evidence was only circumstantial, the population declines were attributed primarily to this mycoplasma infection. Because of concern that movement of desert tortoises for management purposes could spread this disease, strict mycoplasma testing requirements were put in place before any tortoise translocations could occur.
In spite of the intense focus on this disease, the major problem for desert tortoises has always been habitat loss. Solar energy developments in the Mojave Desert are now dramatically accelerating the pace and increasing the scale of habitat loss. Desert tortoises have to be moved out of the way of these developments quickly and efficiently, otherwise they could be buried by earth movers.
While well intentioned, the long-standing diagnostic testing requirements are now causing a significant bottleneck in urgently needed tortoise translocations because of the time and expense required for the testing.
Although surveillance testing can be in important tool in preventing disease spread, diagnostic tests are imperfect and are especially problematic in tortoises, which can take three months or more after infection to develop a positive test. Our challenge, therefore, is to remove this bottleneck so tortoises can be moved out of harm’s way, but without causing inadvertent spread of disease to other tortoises.
In order to address this problem, we took a three-pronged approach. First, we provided evidence that the existing diagnostic testing protocol would not accomplish the goal of preventing movement of Mycoplasma-infected tortoises.
Second, we launched a rapid research effort to identify all of the disease agents of concern in desert tortoises so we could put Mycoplasma infections in their proper context.
Finally, we organized a disease risk assessment workshop, the goals of which were to review all of the available disease data for desert tortoises, assess and prioritize the risks associated with each identified disease agent, and to develop efficient and effective disease risk mitigation strategies that would allow tortoise translocations to proceed in a timely manner.
For the workshop, we assembled a team of experts from across the country and we carefully evaluated each potential disease threat. We then developed more simple and streamlined disease mitigation strategies that don’t involve expensive and time-consuming surveillance tests. This will now allow field biologists to rapidly assess the health of wild tortoises and move them quickly, but safely, to new locations out of harm’s way. Ultimately, our goal is to help secure a future for desert tortoises by removing disease as a roadblock to their recovery and conservation.
Bruce A. Rideout, DVM, Ph.D., DACVP
Director, Wildlife Disease Laboratories
San Diego Zoo Institute for Conservation Research