Scrub typhus

Scrub typhus or Bush typhus is a form of typhus caused by the intracellular parasite Orientia tsutsugamushi, a Gram-negative α-proteobacterium offamily Rickettsiaceae first isolated and identified in 1930 in Japan. Scrub typhus is transmitted by some species of trombiculid mites ("chiggers", particularly Leptotrombidium deliense),^[3] which are found in areas of heavy scrub vegetation. The bite of this mite leaves a characteristic black eschar that is useful to the doctor for making the diagnosis.

Scrub typhus is endemic to a part of the world known as the tsutsugamushi triangle (after O. tsutsugamushi). This extends from northern Japan and far-eastern Russia in the north, to the territories around the Solomon Sea into northern Australia in the south, and to Pakistan and Afghanistan in the west.

The precise incidence of the disease is unknown, as diagnostic facilities are not available in much of its large native range which spans vast regions of equatorial jungle to the sub-tropics. In rural Thailand and in Laos, murine and scrub typhus accounts for around a quarter of all adults presenting to hospital with fever and negative blood cultures The incidence in Japan has fallen over the past few decades, probably due to land development driven decreasing exposure, and many prefectures report fewer than 50 cases per year.It affects females more than males in Korea, but not in Japan, and this is conjectured to be because sex-differentiated cultural roles have women tending garden plots more often, thus being exposed to plant tissues inhabited by chiggers. The incidence is increasing day-by-day in southern part of Indian Peninsula.

Symptoms include fever, headache, muscle pain, cough, and gastrointestinal symptoms. More virulent strains of O. tsutsugamushi can cause hemorrhaging and intravascular coagulation. Maculopapular rash, eschar, splenomegaly and lymphadenopathies are typical signs. Leukopenia and abnormal liver function tests are commonly seen in the early phase of the illness.Pneumonitis, encephalitis, and myocarditis occur in the late phase of illness.

Acute scrub typhus appears to improve viral loads in patients with HIV. This interaction is refused by an in vitro study. There are currently no licensed vaccines available.