My PhD research in a nut [tortoise] shell...

My research aims to determine interactions between ticks, tick-borne pathogens, the Mojave desert tortoise and the Mojave Desert burrow ecosystems. My goals are threefold: 1) Identify ticks found in Mojave Desert burrow ecosystems 2) Model of tick species distribution and pathogen prevalence across the Mojave 3) Determine Borrliacidal (Borrelia killing) effects in desert tortoise blood. 

In the southwestern United States, soft ticks (Ornithodoros spp.) commonly parasitize the threatened Mojave desert tortoise (Gophurus agassizii).  Three Ornithodoros tick species occur throughout the Southwest (O. hermsii, O. parkeri, O. turicata) and desert tortoise habitat. However, most literature classifies ticks found on desert tortoises by genus only. These ticks are difficult to identify microscopically and as a result, the species of these ticks are debated. 

These ticks carry Borrelia, the pathogen that causes tick-borne relapsing fever (TBRF) in a people. TBRF causes periods of high fever for a period of about 3 days, followed by an afebrile period that lasts about 7 days only to be followed by another febrile period. This cycle of febrile and afebrile periods continues until treated with antibiotics. Although tortoise population decline is partially credited to disease, disease and parasitism are not often linked despite extensive parasitism by ticks. This is why my research will focus on developing 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.

No research exists on how ticks and tick-born pathogens interact with desert tortoises. However, the Western fence lizard (Sceloporus occidentalis) is reported to have an enzyme in its blood that has a borreliacidal (Borrelia killing) effect on ticks after they ingest it.  This enzyme is related to a thermolabile protein that destroys spirochetes in the midgut diverticula of feeding ticks. Thus, this enzyme makes the tick incapable of transmitting disease. In areas with a high abundance of western fence lizards there is a reduced risk of transmitting disease.  A thermolabile hemolytic agent (complement) exists in turtle serum, but it’s function has not been studied in tortoises. So far, 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.   This research prove to have important public health impacts as we learn the tortoise’s role in the mitigation of tick-borne disease and the tick’s role in the spread of disease throughout the Mojave desert.
 

Have any questions about my work? Feel free to contact me.