Ticks are large blood-sucking arachnids that transmit pathogens, including bacteria such as Rickettsia japonica, thereby making them a medical concern. In Japan, cases of Japanese spotted fever mainly in Western Japan, have been reported, with outbreaks being reported from few areas such as the Chiba Prefecture. The number of rickettsial infections increases annually. Because of the need to understand the actual situation regarding tick bites in the Chiba Prefecture, we retrospectively investigated 76 patients who presented with tick bites at the Dermatology Department of Kimitsu Central Hospital between July 2012 and August 2023. Patients with tick bites were predominantly older individuals aged 60 years and older, as well as young individuals under 20 years of age. The tick bites tended to occur during spring and summer in rural areas. The lower limbs were the most commonly affected sites, whereas in children, bites were frequently observed on the head and torso. The estimated locations of tick bites in Japanese patients with spotted fever were concentrated in the mountainous areas of the Boso Peninsula, particularly around the Kazusa hill, suggesting that ticks harboring Rickettsia japonica inhabit this region. The number of patients with tick bites in the Chiba Prefecture may continue to increase; therefore, it is necessary to understand and raise awareness about the disease.

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Case: A 7-month-old female infant presented with widespread brown macules that resulted in the development of erythema and urticarial wheals upon scratching. She was initially diagnosed with maculopapular mastocytosis, but the diagnosis was revised to diffuse cutaneous mastocytosis (DCM) due to the development of blisters and erosions on the brown macules. Histopathological examination showed elevated mast cell number in the upper dermis, and immunohistochemical staining for c-kit was positive, confirming the diagnosis. Mast cells are known to release various mediators, including histamine, leukotrienes, and platelet-activating factor, which contribute to the inflammatory response and cutaneous symptoms of mastocytosis. Despite initial treatment with H1 antagonists (levocetirizine and chlorpheniramine), blister formation persisted. The leukotriene receptor antagonist pranlukast was subsequently introduced in addition to the H1 antagonists. This combination effectively suppressed blister formation, leading to rapid healing of the skin lesions. The addition of pranlukast, a leukotriene receptor antagonist, to conventional H1 antagonist therapy effectively reduced blister formation in this case of DCM. These results suggest that targeting leukotriene pathways, in combination with histamine blockade, represent a promising therapeutic approach for managing refractory DCM.

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