us ▁is ▁en demic ▁to ▁a ▁part ▁of ▁the ▁world ▁known ▁as ▁the ▁ts uts ug am ush i ▁triangle ▁( after ▁O . ▁ts uts ug am ush i ). ▁This ▁extends ▁from ▁northern ▁Japan ▁and ▁far - e astern ▁Russia ▁in ▁the ▁north , ▁to ▁the ▁territ ories ▁around ▁the ▁Sol omon ▁Sea ▁into ▁northern ▁Australia ▁in ▁the ▁south , ▁and ▁to ▁Pakistan ▁and ▁Afghan istan ▁in ▁the ▁west . ▁It ▁may ▁also ▁be ▁en demic ▁in ▁parts ▁of ▁South ▁America . ▁ ▁The ▁precise ▁inc idence ▁of ▁the ▁disease ▁is ▁unknown , ▁as ▁di agnostic ▁facilities ▁are ▁not ▁available ▁in ▁much ▁of ▁its ▁large ▁native ▁range , ▁which ▁sp ans ▁vast ▁regions ▁of ▁equ atorial ▁j ung le ▁to ▁the ▁subt rop ics . ▁ ▁In ▁rural ▁Th ailand ▁and ▁La os , ▁mur ine ▁and ▁scr ub ▁ty ph us ▁account ▁for ▁around ▁a ▁quarter ▁of ▁all ▁adult s ▁present ing ▁to ▁hospital ▁with ▁fe ver ▁and ▁negative ▁blood ▁cult ures . ▁ ▁The ▁inc idence ▁in ▁Japan ▁has ▁fallen ▁over ▁the ▁past ▁few ▁dec ades , ▁probably ▁due ▁to ▁land ▁development ▁driving ▁decre asing ▁expos ure , ▁and ▁many ▁pre fect ures ▁report ▁fewer ▁than ▁ 5 0 ▁cases ▁per ▁year . ▁ ▁It ▁affect s ▁females ▁more ▁than ▁males ▁in ▁Korea , ▁but ▁not ▁in ▁Japan , ▁which ▁may ▁be ▁because ▁sex - d iffer enti ated ▁cultural ▁roles ▁have ▁women ▁t ending ▁garden ▁plots ▁more ▁often , ▁thus ▁being ▁exposed ▁to ▁veget ation ▁inhab ited ▁by