Comparison of DNA and Carbon and Nitrogen Stable Isotope-based Techniques for Identification of Prior Vertebrate Hosts of Ticks.

Identification of the vertebrate hosts upon which hematophagous arthropods feed provides key information for understanding the ecology and transmission of vector-borne diseases. Bloodmeal analysis of ticks presents unique challenges relative to other vectors, given the long interval between bloodmeal acquisition and host-seeking, during which DNA degradation occurs. This study evaluates DNA-based and stable isotope-based bloodmeal analysis methodologies for the lone star tick, Amblyomma americanum (Linneaus, 1758), in an experimental study with chicken as the known host. We subjected ticks of different ages and environmental rearing conditions to three DNA-based approaches and a stable isotopic analysis, which relies on the natural variation of nitrogen ((15)N/(14)N) and carbon ((13)C/(12)C) isotopes. While all three DNA-based approaches were successful in identifying the bloodmeal host of the engorged nymphs, only the probe-based RT-PCR was able to detect host DNA in aged ticks, the success of which was low and inconsistent across age and rearing treatments. In contrast, the stable isotope analysis showed utility in determining the host across all ages of ticks when isotopic values of ticks were compared with a panel of candidate vertebrate species. There was a positive shift in both δ(13)C and δ(15)N in adult A. americanum until 34 wk postnymphal bloodmeal. Through analyzing the isotopic signatures of eight potential vertebrate host species, we determined that the magnitude of this isotopic shift that occurred with tick age was minor compared with the heterogeneity in the δ(15)N and δ(13)C signatures among species. These results suggest that stable isotopes are a useful tool for understanding tick-host interactions.