Reemergence of Scrub Typhus Associated with Leptotrombidium akamushi Mites and Karp-Like Orientia tsutsugamushi Genotype Bacteria, Japan, 2024-2025.

Scrub typhus is a miteborne infectious disease caused by Orientia tsutsugamushi bacteria. In Japan, most cases occur in spring and autumn and are transmitted by Leptotrombidium pallidum and L. scutellare mites; summer scrub typhus, transmitted by L. akamushi mites, is rarely reported. In August 2024, a pregnant woman had scrub typhus develop after attending a fireworks event in Niigata Prefecture, Japan, resulting in fetal death. A Vietnam-related Karp-like O. tsutsugamushi genotype, distinct from the Kato type usually associated with L. akamushi mites, was detected from patient samples. Field investigations at the site of the fireworks event revealed seasonal predominance of L. akamushi mites in summer. We detected O. tsutsugamushi sequences identical to the patient's strain in 3 L. akamushi mite larvae and 1 field mouse, suggesting that L. akamushi mites were the source of human infection. Our findings suggest reemergence of summer scrub typhus associated with infected L. akamushi mites carrying a locally novel genotype.