Tick bite: don’t pick the wrong microbe!

Scalp pathology
Infectious dermatosis

Dr. Emmanuelle Bourrat

Saint-Louis Hospital

The clinical case
Now it's your turn!
Co-prescription and advice

Clinical case presentation

This young girl, on vacation in south-west France, had had a large tick removed from her scalp by her GP after it had been present for several days. Her GP prescribed local antiseptic treatment and, as a preventive measure, antibiotic therapy with amoxicillin for 14 days.

At the end of this treatment, she presented with a crusted lesion, adherent at the bite site, surrounded by a mildly inflammatory ring of alopecia. She had no systemic symptoms, but there was a tender 1.5 cm ipsilateral retroauricular cervical lymph node.

Suspecting a superinfected tick bite, a second-line course of antibiotics (amoxicillin-clavulanate) was prescribed, which was as ineffective as the first.

Your turn

What is your diagnosis?

Select 1 answer(s) from the following choices:

Lyme borreliosis

TIBOLA rickettsiosis

Mediterranean spotted fever rickettsiosis

Babesiosis (or piroplasmosis)

Wrong answer!

Good answer!

Selected diagnosis

Despite a negative Rickettsia serology (which is very inconsistently positive), this young patient met all the major diagnostic criteria for TIBOLA (Tick-Borne Lymphadenopathy): bite from a large tick on the upper part of the body (90% on the scalp), a fixed necrotic inoculation eschar surrounded by an erythematous halo (15% larger than 5 cm) and painful regional lymphadenopathy (occipital, cervical). On the other hand, she had none of the minor, non-specific criteria (fever, fatigue, joint and muscle pain, rash).

The rapidly favorable response to macrolides is an additional argument. This inoculation dermatosis transmitted by a tick of the genus Dermacentor is not a borreliosis but a clinical entity associated with several intracellular bacteria: Rickettsia slovaca is the main causative agent in France, but Bartonella henselae and Francisella tularensis produce identical clinical pictures.

Explanation of wrong answers

This presentation bears no resemblance to a primary stage (erythema chronicum migrans) or secondary stage (borrelial lymphocytoma) of Lyme borreliosis.
Mediterranean spotted fever is also a rickettsiosis found in the south of France. It manifests as a febrile papular exanthem involving the palms and soles, accompanied by headache, arthralgia and myalgia.
Babesiosis, or piroplasmosis, is a rare parasitic infection in humans, also transmitted by ticks, and sometimes severe in immunocompromised patients. Its symptoms include fever, jaundice and hemoglobinuria.

Treatment

Treatment is based on oral tetracyclines or, in young children or pregnant women, macrolides: treatment with azithromycin 10 mg/kg/day led to rapid resolution of the adenopathy, the crust and regrowth of the hair.

Message from the expert

The microorganisms transmitted by ticks are many and varied (viruses, bacteria, parasites), but the risk of transmitting infectious agents to humans following a tick bite is estimated to be less than 3%.

References :

^{E Rigal and col TIBOLA a rapidly expanding clinically polymorphic ricketisiosis. Ann Dermatolol Venereol 2014; 141: 186-191}