Heuristic rules for cooperative transport in wood ant nest maintenance.

Scrub typhus is a mite-borne rickettsial disease caused by () and transmitted to humans by larval trombiculid mites. It is endemic in Asia, particularly within the “Tsutsugamushi Triangle,” and its epidemiology is strongly influenced by geographic location, seasonality, and vector distribution, with increasing recognition of scrub typhus cases beyond traditionally endemic areas, likely reflecting previously unrecognized endemicity rather than true geographic spread. The clinical spectrum of scrub typhus is broad, ranging from mild illness to fatal disease. Although fever, rash, and eschar are considered characteristic findings, these manifestations are not universally present, and cases lacking typical features may be easily overlooked. Early diagnosis is essential because severe complications, such as acute respiratory distress syndrome, acute kidney injury, and meningitis, can be life-threatening. A case in which scrub typhus was suspected based on epidemiological exposure and clinical course despite the absence of rash and eschar is reported, and similar cases are reviewed to emphasize the diagnostic challenges of atypical presentations. A 65-year-old Japanese woman presented with persistent xerostomia (dry mouth). Thirty days before admission, in March 2023, she had walked along a mountain trail while picking mandarins in Shimabara, Nagasaki Prefecture, where scrub typhus cases had been reported during the previous late fall to winter season. She reported no known exposure during that period. Fifteen days later, she developed a high fever of ∼39°C accompanied by fatigue and xerostomia. The fever and fatigue resolved spontaneously, but dry mouth persisted, and progressive polyuria prompted medical evaluation. She had no significant past medical history, including scrub typhus, and was not taking medications. On admission, she was afebrile (maximum temperature 37.5°C), and her vital signs were stable. A physical examination revealed marked dryness of the oral mucosa, hepatosplenomegaly, and right inguinal lymphadenopathy. No rash or eschar was identified, including on the scalp, ear canals, axillae, umbilicus, or external genitalia.