however, RAGE contains a number of genes including tra genes typical of type IV secretion systems and gene for ankyrin repeat–containing protein. Ankyrin repeat–containing proteins are secreted through a type I secretion system into the host cell. The precise role of type IV secretion system in O. tsutsugamushi is not known. It may be involved in horizontal gene transfer between the different strains. Life cycle and transmission Orientia tsutsugamushi is naturally transmitted in the mite population belonging to the genus Leptotrombidium. It can be transmitted by a female to its eggs through the process called transovarial transmission, and from the eggs to larvae and adults through the process of transstadial transmission. Thus, the bacterial life cycle is maintained entirely in mites. Infection to rodents and humans is an accidental transmission from the bite of mite larvae, and not required for reproduction or survival of the bacterium. In fact, in humans the transmission is stopped, and the bacterium meets a dead end. However, uninfected mites can acquire the infection from infected rodents. In rodent and human infections, Leptotrombidium deliense is the most common vector of O. tsutsugamushi. L. pallidum, L. fletcheri and L. scutellare are also carriers in many countries. In addition, L. akamushi is an endemic carrier in Japan, L. chiangraiensis and L. imphalum in Thailand, L. gaohuensis in China, and L. arenicola in Malaysia and Indonesia. In parts of India, a different mite species, Schoengastiella ligula is also a major vector. The life cycle of mites consists of egg, prelarva, larva, protonymph, deutonymph, tritonymph, and adult. The larvae, commonly referred to as chiggers (Figure 4), are the only ectoparasitic stage feeding on the body fluids of rodents and other opportunistic mammals. Thus, they are the only stage in the life of mites that transmit the infection. Wild rats of the genus Rattus are the principal natural hosts of the chiggers. Chiggers feed only once on a mammalian host. The feeding usually takes 2 to 4 days. In contrast to most parasites, they do not feed on blood, but instead on the body fluid through the hair follicles or skin pores. They possess a special feeding apparatus called a Stylostome, which is a tube formed by solidified saliva. Their saliva can dissolve the host tissue around the feeding site, so that they ingest the liquefied tissue. O. tsutsugamushi is present in the salivary glands of mites and is released into