Sunday, August 9, 2015

Answer to Case 360

Answer: Amblyomma americanum, the Lone Star tick.

An important clue to this case is the presence of a single macula (dot or 'lone star') on the dorsum of the tick from which its name is derived. It is important to keep in mind, however, that other ticks can have maculae on their dorsal surface and therefore characteristics of the the anal groove and mouth parts, as well as the presence or absence of festoons are important for confirming the identification of the tick. Festoons can be particularly challenging to appreciate when the tick is engorged such as in this case, but they can usually be seen using careful examination with a dissecting microscope and lateral light. Below, the presence of faint shadows suggest the presence of festoons (arrow heads).

The CDC has a nice genus-level pictorial tick key that you can access here:

Some of you might have been slightly thrown off by the geographic location of this tick (Connecticut). Despite it's name, the Lone Star tick has a distribution far outside of the 'Lone Star state' of Texas. In fact, the range now expands far up into the north east and north central states, and is approaching the upper midwest.
Map from the CDC (
Amblyomma americanum are aggressive biters and are vectors of the organisms causing ehrlichiosis, tularemia and STARI. Their geographic range continues to expand, therefore increasing the number of individuals potentially at risk for A. americanum-transmitted diseases.

Thanks again to Dr. Sheldon Campbell for donating this case.

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