This 6-year research program aims to understand the ecological drivers for the geographic variation in Lyme disease risk in eastern North America. More information is available at http://lyme-gradient.tennessee.edu
CNN has a recent article about Powassan virus, spread by blacklegged ticks: http://www.cnn.com/2017/05/03/health/powassan-tick-virus/index.html Here's a map of the locations of Powassan cases in recent years. While the article claims "everyone" is at risk, there is in fact currently no significant risk of this disease for folk in southern states. I know of one report of a patient being treated for Powassan in TN, however I checked with the doctor involved, who says the child contracted the infection on Long Island NY.
Regional variation in tick-borne disease risk deserves more attention than it gets.
For those in Lyme-endemic areas, the risk in late spring through summer comes from the nymphal (teenage) life-stage of the blacklegged tick. The media almost always uses images of the adult ticks in articles about tick-borne disease - be aware that the nymphs are much smaller!
These tick larvae, photographed in mid-January in Tennessee, fed on mouse blood back in September. They spend the winter buried deep in the leaf litter, waiting for Spring and the opportunity to molt into host-seeking nymphs.
Tick eggs hatch into larvae that have 3 pairs of legs (unlike the nymphs and adults that have 4 pairs). Larvae feed once on a host such as a mouse, usually in late summer, at which point they are refered to as "engorged".
These engorged larvae, full of mouse blood, may molt in nymphs within a few weeks, or later in the year may choose to overwinter and not emerge until the following Spring.
Rebecca Eisen and colleagues from the CDC have updated the well-known Dennis et al. (1994) black-legged tick distribution map. Data for counties in several states, particularly Tennessee and Michigan, were contributed by the Lyme Gradient team.
The distribution of tick sightings across the United States between a) 1907–1996 and b) 1907–2015 (D. T. Denniset al.,J. Med. Entomol.1998; R. J. Eisenet al.,J. Med. Entomol.2016).
These engorged female blacklegged ticks fed on deer during the first week of November, and over the past 5 weeks have been converting the blood meal into a clutch of up to 2000 eggs. Now they are beginning to oviposit, down in the leaf litter.