Tick bite

ID: 36y/o ♀ otherwise healthy with a suspected tick bite in the ER; 

HPI: was camping in the woods; noticed a mildly painful, small, round, red skin lesion on her thigh; did not see the tick, but is concerned; wants to know if she needs any tests for lyme disease; no fever/chills; ROS non contributory; 

E/O: Looks well; not ill/toxic; VSSA;

A round, well circumscribed, indurated red papule on the Rt medial thigh; mildly tender to touch; no surrounding erythema or bull’s eye appearance; 

A/P: suspected tick bite; daxycyclin 200mg po once; f/u precautions; testing for lyme disease is not recommended; 

Discussion^(1,2): 

Factors affecting disease transmission: 

1. Tick species and stage of development: nymphal stage of deer tick (Ixodes scapulars); 
2. Season: late spring, early summer; 
3. Engorgement: transmission needs >36hr of feeding; tick on the skin needs 24hr before it starts feeding; 

How to remove a tick from skin: 

Grasp the tick with a fine forceps as close to skin as possible; pull straight up; if mouth pieces (does not increase transmission) remain do not try removal (to prevent trauma to skin); do not use other methods such as burning or using chemicals (may irritate the tick ➜ act as a syringe ➜ injects the organism into the host ➜ increases the risk of transmission)

Erythema migrans (EM)⁽³⁾: Characteristic lyme disease rash; bull’s eye appearance; 

Approach to prophylaxis as per Infectious Diseases Society of America (IDSA) guidelines: antibiotic prophylaxis is indicated if the patient meets all the following criteria,

1. Adult or nymphal Ixodes scapularis tick (deer tick).
2. attached for ≥36 hr;
3. Prophylaxis given within the first 72 hours of tick removal.
4. Local rate of infection of ticks with B. burgdorferi is ≥20 percent;
5. No contraindications for Doxycycline (<8 y/o, pregnant, or lactating).

If the patient meets all of these criteria, give doxycycline 200 mg po once (4 mg/kg po once in children >8y/o max dose 200mg). If any contraindications, then no prophylaxis is recommended; 

IgM to B. burgdorferi appears 1-2wk after the signs and sx of lyme disease; IgG appears 2-6wk after the onset of EM; 

  

References: 

1. http://www.cdc.gov/lyme/transmission/blacklegged.html
2. http://www.uptodate.com/contents/evaluation-of-a-tick-bite-for-possible-lyme-disease?source=search_result&search=tick+bite&selectedTitle=1%7E86
3. http://www.bada-uk.org/wp-content/uploads/Erythema_migrans1.jpg