Molecular Identification of Otherwise Unidentifiable “Brown Legged” Rodent Ticks

Biology Honors project funded in part by Department of Biological Sciences (Rachel Niemiec).

Ticks have a profound impact on human health due to the pathogens they carry. For this reason, it is important to know which species are collected from different animal that may serve as reservoirs.

There are three prominent species of “brown legged” ticks in the Hampton Roads area. They are the Gulf Coast tick, Amblyomma maculatum, the Lone Star tick, Amblyomma americanum, and the dog tick, Dermacentor variablis. Each of these ticks is different in its host preference, as well as the pathogens they are able carry and transmit (see information in the "Its tick time" blog posting). This project uses different molecular methods to identify brown legged ticks collected from rodents at several different sites. Identification through morphology can be difficult when the tick is engorged or missing mouth parts from ticks in their first two life stages.

During this study DNA was extracted from the ticks, amplified using PCR, and analysed following restriction enzyme digestion (restriction fragment length polymorphism - RFLP). We also tested the extracted DNA for the presence of Rickettsial DNA .

RFLP analysis indicated that we were able to differentiate the three brown legged ticks found in this area- Dermacentor variabilis, Amblyomma maculatum and A. americanum. We had trouble amplifying DNA from some of the ticks; this may have been due to degradation of DNA over time as many of the ticks had been stored for a number of years.  Most of the ticks tested from rodents were identified as Dermacentor variabilis indicating a preference of the immature stages of this tick for rodents. 

Approximately 25% of the ticks tested were positive for the presence of rickettsial DNA; the species of Rickettsia is unknown at this time.