Geographical distribution, effect of season & life cycle of scrub typhus.

Introduction Scrub typhus is an infectious disease caused by Orientia tsutsugamushi, a tiny parasite about the size of bacteria that belongs to the family Rickettsiaceae. Scrub typhus was first described by Hashimoto from Japan in 1899 (1). The term scrub is used because of the type of vegetation (terrain between woods and clearings) that harbours the vector; however, the name is not entirely correct because certain endemic areas can also be sandy, semi-arid and mountain deserts (2,3). It is reported most often from Southeast Asia and Japan and is the most commonly reported rickettsial infection in India. Globally over one billion people are at risk for scrub typhus and an estimated one million cases occur annually (1).Scrub typhus is also known as tsutsugamushi disease. The name tsutsugamushi is derived from two Japanese words: tsutsuga, meaning something small and dangerous, and mushi, meaning creature. The infection is called scrub typhus because it generally occurs after exposure to areas with secondary (scrub) vegetation. It has recently been found, however, that the disease can also be prevalent in such areas as sandy beaches, mountain deserts, and equatorial rain forests. Therefore, it has been suggested that the names miteborne typhus, or chigger-borne typhus, are more appropriate. Since the disease is limited to eastern and southeastern Asia, India, northern Australia and the adjacent islands, it is also commonly referred to as tropical typhus Fig 1. Tsutsugamushi Triangle