Sunday, June 25, 2017

Answer to Case 450

Answer: Dermacentor variabilis

The CDC has a nice basic pictorial identification key that you can access HERE. This key will walk you through the identifying features of hard ticks, and Dermacentor species specifically. Differentiating D. variabilis from D. andersoni (and other Dermacentor spp.) is a bit trickier and is based on the size and number of goblets on the spiracular plates; while Dermacentor variabilis has more than 300 small goblets, D. andersoni has 100-200 moderately sized goblets.

I particularly like Ellen's analogy, in which she described the goblets of D. variabilis as 'grainy' while those of D. andersoni resemble Cheerios.

The location where this tick was found (Manitoba, Canada) also helps differentiate the two. Dermacentor variabilis has undergone a range expansion in the Canadian Prairies since the 1960s (see Dergousoff et al. J Med Entomol 2013) so that D. variabilis is the species we would expect to see in Manitoba.

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