ABOUT TICKS
Ticks are arachnids, which are a class of arthropods that includes ticks, spiders, mites, and daddy longlegs. Ticks in North America fall into one of two families, the hard ticks and the soft ticks. Of these two, the hard ticks (Family: Ixodidae) are of the greatest medical relevance to humans. In Ohio, there are six species of medically important hard ticks: The American Dog Tick (Dermacentor variabilis), the eastern Blacklegged Tick (Ixodes scapularis), the Lone Star Tick (Amblyomma americanum), the Brown Dog Tick (Rhipicephalus sanguineus), the Gulf Coast tick (Amblyomma maculatum), and the Asian Longhorned tick (Haemaphysalis longicornis). Among these, only the first two are currently established in Tuscarawas County.
BLACKLEGGED TICKS
Our current research focuses on the Eastern Blacklegged Tick (Ixodes scapularis). This is the tick species that is able to pass the bacteria that causes Lyme Disease (Borrelia burgdorferi) between humans and other animals, so there is a lot of interest in understanding the ecological factors that explain Blacklegged Tick abundance, Borrelia prevalence within BLT populations, and disease risk to humans.
Blacklegged Ticks have exploded across Ohio since the first population was discovered in Coshocton County in 2010, and little is known about the prevalence of Borrelia in tick populations anywhere in Ohio. Our goal is to create a high resolution map of Borrelia prevalence within tick populations of Tuscarawas County, Ohio and to evaluate landscape factors that may be important for predicting Lyme Disease risk.
LIFE HISTORY OF THE BLACKLEGGED TICK
The key to understanding any species is to know its life history. Like most hard ticks, Blacklegged Ticks (BLTs) have a life history that consists of 4 distinct life stages: egg, larva, nymph, and adult. Ticks feed only once at each life stage. Larvae are active in mid-summer, hatching from eggs laid by adult females the previous winter. They tend to feed on small mammals and birds, and once fed, descend to the leaf litter for a long metamorphosis. After overwintering, larvae metamorphose into nymphs and emerge during the spring and early summer. These ticks are only a bit larger than larvae and feed on a wider range of hosts, including humans. After feeding, nymphs return to the leaf litter and metamorphose into adults, which emerge in late autumn and are active through the winter. This life cycle takes approximately 2 years to complete.
LIFE HISTORY OF A DISEASE
Lyme Disease is caused by a spirochete bacteria called Borrelia burgdorferi (and also by a few other Borrelia species). The habitat of Borrelia is the internal world of vertebrate bodies, and Borrelia is known to be capable of surviving in a wide variety of species of mammals, birds, and lizards. In our region, the best known host species for Borrelia are mice in the genus Peromyscus (Deer Mice or White-footed Mice). White-tailed Deer, which are important hosts for adult BLTs, turn out to be bad habitats for Borrelia, with immune systems that are pretty efficient at eliminating infections. In order for Borrelia to survive in the landscape, it must have a way of getting from one suitable host to another, and the vehicle that they use for this purpose are Blacklegged Ticks. BLTs are generally not born infected with Borrelia, and so they must acquire Borrelia through feeding. This infection could be acquired at any or all three of their blood meals; once infected, ticks remain infected and infectious, so it is the nymphs and the adults that pose a risk of Lyme Disease.
Photo: Deer Mouse (Peromyscus maniculatus) from Missouri Department of Conservation