Host factors associated with blood parasite infections in aquatic turtles in Georgia

Student Candace Cooper worked with Professor Michael Yabsley during summer 2013 studying Haemogregarine parasites in turtles. This is the abstract from her summer project.

Abstract. Haemogregarines are common intraerythrocytic protozoan parasites of reptiles. Of the four genera of haemogregarines that infect reptiles, Haemogregarina is the most common genus reported from aquatic turtles. The life cycle of these parasites includes leeches as definitive hosts and vectors and aquatic turtles as the intermediate hosts. Previous research has suggested that turtle behavior may play a role in risk of infection and parasitemia with Haemogregarina spp. The objective of this study was to better understand what factors (e.g. basking habits, seasonality, etc.) affect both parasitemia and prevalence of infection. Additionally, to determine if multiple Haemogregarina spp. infect aquatic turtles, we genetically characterized a subset of samples. We hypothesized that Haemogregarina infection prevalence and parasitemia levels would differ between basking and non-basking turtle species and with season as both factors would alter contact rates with leeches. Six different aquatic turtle species were trapped with baited hoop nets in eight locations in Clarke County, Georgia. Giemsa-stained blood smears were analyzed to determine prevalence of haemogregarines and parasitemias based on number of infected cells per 7,000 cells examined. To date, significantly higher prevalence were noted for non-basking species (n=103, 88%) compared with basking species (n=286, 43%). Similarly, non-basking species (0.41%) had significantly higher parasitemias compared with basking species (0.016%). Among the four most commonly sampled species, the non-basking musk turtles (Sternotherus odoratus and S. minor) (0.51%) had higher parasitemias (p=0.0001) compared with the non-basking common snappers (Chelydra serpentina) (0.147%). The parasitemias of the three basking species were different with sliders (Trachemys scripta) (0.022%) having significantly higher parasitemia (p=0.028) than painted turtles (Chrysemys picta) (0.012%) and river cooters (Pseudemys concinna) (0.007%). No differences in prevalence or parasitemia were noted between genders. These data support the importance of turtle behavior (basking or non-basking) in prevalence and parasitemia levels. Lower prevalence and parasitemias in basking species could be attributed to a reduction in leech exposure, an increase in the host immune response, biology of different haemogregarine species, or another unknown factor. To address Haemogregarina species diversity, a segment of the 18s rRNA region (~600bp) was amplified and sequenced. Sequences were highly similar but three groups, possibly different species of Haemogregarina, were identified. Each group contained a diversity of turtle species (including basking and non-basking species) and five turtles showed evidence of infection with two different strains. Additional research is needed to better understand the ecology of these understudied parasites of turtles.

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