Rickettsia parkeri spotted fever and toxicosis by Ornithodoros: other tick bite-related entities to be known by dermatologists

Dear editor,

We have read with great interest the recent review written by Haddad et al. (2018), regarding skin manifestations caused by tick bites, published in Anais Brasileiros de Dermatologia, in which the authors propose a clinical classification of these manifestations considering "primary lesions" (PL) and "secondary lesions" (SL).¹ To their list, we would like to suggest the inclusion of two other emerging clinical entities, still little known to health professionals in Brazil: Rickettsia parkeri spotted fever (RPSF) as a SL and toxicosis by Ornithodoros as a PL.

RPSF occurs predominantly in Atlantic rainforest areas of South, Southeast, and Northeast Brazilian regions. R. parkeri strain Atlantic rainforest is the causative agent of this condition, which is transmitted to humans by Amblyomma ovale ticks. (Figure 1A).² Clinical manifestations of R. parkeri infection tend to be less severe than R. rickettsii rickettsiosis, associated with fever, inoculation eschar, rash, lymphadenopathy, malaise, headache, myalgia, and arthralgia.² Inoculation eschar (main sign) is defined as a painless ulcer lesion with a crusty-necrotic center and a surrounding erythematous halo, measuring 0.5 - 2 cm in diameter, which indicates the site of the tick bite (Figure 1B).^2,3 Doxycycline is the drug of choice for all suspected spotted fever cases, regardless of age group and disease severity.²

Figure 1:

A - A female of Amblyomma ovale (Source: Álvaro A. Faccini-Martínez). B - Inoculation eschar in a patient with spotted fever caused by Rickettsia parkeri strain Atlantic rainforest. (B - 1) 12 days after the tick bite (DATB). (B - 2) 14 DATB. (B - 3) 23 DATB. (B - 4) 30 DATB (Source: Krawczak, et al., 2016⁽³⁾)

Ornithodoros ticks, in turn, is a genus in the soft-bodied tick family (Argasidae) that has gained medical importance for their capacity to cause toxicosis,⁴ or for being borreliosis (relapsing fever) vectors.⁵ These ticks are natural parasites of mammals (mainly rodents) and birds living in caves, tree hollows, nests, and attics of houses. Ticks become infected when they feed on animals (primary hosts) that carry the bacterium in their blood. The disease is transmitted to humans by the bite of infected ticks.⁶ In Brazil, toxicosis in humans has been reported in the states of Rio Grande do Sul, Minas Gerais, Goiás, Pernambuco, Rio Grande do Norte, and Ceará, with Ornithodoros brasiliensis, O. mimon, and O. rietcorreai as the related tick species (Figure 2A).^7-9 The most common clinical manifestations included local pruritus, edema and erythema, blister lesions, and systemic involvement (transient fever, dyspnea, and malaise) (Figure 2B-C).^4,7 Topical or systemic corticosteroids and antihistamines may be used as treatment options.⁴

Figure 2:

A - A female of Ornithodoros rietcorreai associated to human parasitism and toxicosis, collected in residences in the urban area of Russas, State of Ceará (Source: Stefan Vilges de Oliveira). B - Skin lesion (heel) by Ornithodoros brasiliensis bite, State of Rio Grande do Sul (Source: José Reck Jr., et al., 2013 ) C - Bullous lesion on the wrist caused by O. mimon bite, State of Minas Gerais (Source: Labruna, et al., 2014⁽⁸⁾; by permission of Oxford University Press journal)

Both clinical entities presented here should be considered in the medical evaluation of tick bite-associated lesions. In such cases, dermatologists may contribute to the diagnosis of these diseases.