About This Project

Ornithodoros ticks occur in the Mojave desert and frequently parasitize desert tortoises. These ticks carry the pathogen Borrelia, which is responsible for tick-borne relapsing fever. We aim to determine pathogen prevalence and species of ticks collected from tortoises to further understand infection kinetics of Borrelia in tortoises. Borrelia may cause disease in tortoises, but it's also possible there is an enzyme in tortoise blood that kills Borrelia.

Ask the Scientists

What is the context of this research?

An enzyme found in lizard blood reportedly kills Borrelia once a tick ingests it (Lane and Quistad 1998). This enzyme makes the tick incapable of transmitting disease, but there is no research of this borreliacidal enzyme in tortoises. We have tested a sub-sample of 170 ticks collected from tortoises for Borrelia, all tested negative for the pathogen. These ticks were collected from habitats where a known human infection occurred. Thus, we hypothesize there is a factor in tortoise blood interacting with Borrelia in the tick similar to the enzyme found in lizards. Even the species of these ticks are debated, as they are difficult to I.D. (Jacobson 1994). This research will support tortoise conservation and improve public health.

What is the significance of this project?

Mojave desert tortoises are listed as threatened by the U.S. Fish and Wildlife Service and vulnerable by the IUCN. Tortoises are parasitized by ticks that carry Borrelia which causes tick-borne relapsing fever. TBRF is endemic in the western U.S. and reported in tortoise habitat. Although tortoise population decline is partially credited to disease, disease and parasitism are not often linked despite extensive parasitism by ticks. This is why we will create a model of tick distribution and tick-borne disease prevalence throughout the Mojave desert which will be used to understand zoonotic disease dynamics of tick-borne vectors in tortoises in the Mojave desert, hopefully improving public health and encourage conservation of the desert tortoise.

What are the goals of the project?

The goals of this project are threefold: 1) Identify ticks found in Mojave Desert tortoise habitat, 2) Model tick species distribution and pathogen prevalence across desert tortoise habitats, 3) Determine borreliacidal (Borrelia killing) effects in desert tortoise blood. These aims will identify ticks and tick-borne pathogen prevalence in desert tortoise habitats and test hypotheses regarding mechanisms involved in borreliacidal components of tortoise blood. We aim to sample 1000 ticks collected throughout tortoise habitats and conduct in vitro Borrelia killing experiments on desert tortoise blood sampled from captive tortoises. This data will help us understand the tortoise's role in its relationship between ticks and tick-borne disease throughout the Mojave ecosystem.