Behind the resurgence of scrub typhus fever
Scrub typhus has been known to mankind for centuries. The first documented reports of scrub typhus from India date back to 1946 and were from Assam-Burma border. The disease occurs in an area called ‘Tsutsugamushi Triangle’, with Japan in the east, Afghanistan and Middle-East region in the west and the pacific islands area, north Australia, Indonesia, south-east Asia, China, Korea in between. It is caused by a bacterium called Orientia tsutsugamushi.
It belongs to a group which is smaller than bacteria but larger than viruses. The occurrence of the disease is a result of an interaction between bacteria, environment and humans. The word ‘typhus’ has been derived from the Greek word ‘typos’ which means fever with stupor. The earliest medical accounts of typhus were written by Girolamo Cardano, an Italian physician, in 1536; in 1578, Johannes Coyttarus, dean of the faculty of the University of Poiters in France, suggested that typhoid and typhus were different diseases.
Scrub typhus is transmitted to humans by interaction with animal (a zoonotic disease). Japanese folklore knew it to be associated with the jungle mite or chigger, which was for this reason named ‘dangerous bug’ (tsutsugamushi). In 1810 the Japanese Hakuju Hashimoto described a tsutsuga (disease) along the tributaries of the Shinano river. A similar disease, thought to be carried by mites, or mushi in Japanese, had also been known at least since the 16th century in southern China.
During World War II, the incidence of scrub typhus rose dramatically among military troops, reaching 900 per 1,000 personnel in some areas. The larval forms of mites (trombiculid mites) act as reservoir for the bacteria (vector). These larvae feed on wild rats which reside in zones of scrub growth. These zones are often made up of secondary ‘scrub’ growth, which grows after clearance of primary forest; hence the term ‘scrub typhus’. However, mites can survive on seashore, in rice fields and in semi desert areas also. These mites probably act as the major reservoir of the organisms and are capable of transmitting the disease.
Down to Earth