Sunday, June 17, 2012

Answer to Case 212

Answer:  Ixodes scapularis tick (a.k.a. deer tick, black-legged tick), female, not engorged.  Mouthparts are intact. Congratulations to everyone who wrote in - you all had the correct answer.

The answer to the second question I posed, "What would be your advice to this physician?" is a bit trickier.  Thank you for all of the thoughtful responses to this post. 

In advising physicians about prophylaxis or treatment for tick borne illnesses, I refer to the Infectious Diseases Society of America (IDSA) guidelines (Wormser et al., CID 2006) which state that "for prevention of Lyme disease after a recognized tick bite, routine use of antimicrobial prophylaxis or serologic testing is not recommended."  Instead, a single dose of doxycycline may be given for prophylaxis in certain cases; cases should meet the following criteria:

1.  Patient is >/= 8 years of age
2.  The attached tick is identified as I. scapularis (hence the utility of laboratory identification)
3.  The tick is estimated to have been attached for >/= 36 hours (based on degree of engorgement or patient exposure history)
4.  Prophylaxis can be started within 72 h of the time that the tick was removed
5.  Ecologic information indicates that the local rate of infection of these ticks with B. burgdorferi >/= 20%
6.  Doxycycline is not contraindicated

Prophylaxis for other tick-borne diseases (e.g. anaplasmosis, babesiosis) is not recommended.

In this case, the tick is clearly not engorged and was reported to be atached for only 6 hours.  Therefore, I advised the patient (in this case, a physician) to not take any further steps at this point, but to watch for signs and symptoms of tick-borne illness such as rash, myalgias, headache and fever, and to see his physician if any of these arise.

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