Things like climate change and wildlife management practices are thought to be a factor.
(warmer winters->less ticks die, more deer->more deer ticks)
I already know I will find that more sensitive tests for tick borne diseases have been developed so essentially the definition of these diseases has changed, funding for surveillance has increased, the methods of counting ticks have become more sensitive, etc.
EDIT:
Yep, this looks like a good starting point if anyone is interesting in trying to figure out what is really going on. I'm not sure if I will bother:
"A later surge in interest in ticks and tick-borne pathogens has been inspired by recent claims about the impact of forecasted climate change on the spatial distribution of ticks and associated pathogens (Brownstein et al., 2003; Ostfeld et al., 2005; Diuk-Wasser et al., 2006; Ogden et al., 2008; Jaenson et al., 2009). However, this research has been fraught with difficulty from the outset because of insufficient knowledge about the nature of many tick-pathogen associations (Randolph, 2009; Franke et al., 2013; Medlock et al., 2013). A proper understanding of how abiotic factors shape the transmission cycles of tick-transmitted disease agents awaits a more rigorous analysis that is often limited by the current availability of data and the many indirect mechanisms that bear on them (Kahl et al., 2002; Eisen, 2008).
We assume that the many procedural and analytical errors in current tick and tick-borne zoonotic disease research are often a consequence of a lack of knowledge or of suitable training.
[...]
Typical problems include errors in tick identification (especially of immature instars), premature or erroneous reporting of ticks as new vectors and hosts as reservoirs, superficial data on the abundance and seasonal activity of ticks, inappropriate use of statistical methodology, and uncontrolled laboratory diagnostic procedures. The very ready accessibility of research publications online, at least in abstract form, tends to exacerbate the situation in that, as a result of superficial reading and subsequent citing, an erroneous conclusion can quickly become embedded in the literature. "
The entire ecosystem has been overmanaged to reduce predators, and the consequences are dire.
