A tick living in your county does not mean the disease does

Of the many tick species in the world, **only a few bite people and transmit
the bacteria, viruses and parasites that cause human disease.** The CDC
publishes maps of where those few are distributed across the contiguous United
States.

The caveat that comes with the maps

**Even though a specific tick species is found in a region of the United
States, it does not necessarily mean it transmits a specific disease in that
area. Disease transmission is influenced by multiple factors beyond mere
tick presence.**

A tick transmits a pathogen only if the pathogen is circulating in the local
animal hosts it feeds on. The same species can be abundant in two states and
a meaningful risk in only one.

So a distribution map answers "could this tick be here", not "is this disease
here" — and reading it as the second is how a risk gets over- or
under-estimated.

For detailed information about ticks in your county, the interactive tick
surveillance maps are the right source.

Two boundary notes

• Populations may be found outside the shaded areas. A map is a summary,
  not a fence.
• Naturally occurring populations of these ticks do not occur in Alaska —
  though the brown dog tick occurs in Hawaii.

An example of how granular this gets

The American dog tick was recently split into two species. ***Dermacentor
variabilis*** is widely distributed east of the Rocky Mountains, with
limited areas to the west; the newly described D. similis is found
west of the Rockies.

**More research is needed to understand the role of these species in disease
transmission** — which is the same caveat again, now applying to a species
that did not formally exist until recently.

Source: Centers for Disease Control and Prevention.