Excerpt from Scrub Typhus

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Background

Scrub typhus typically occurs in Southeast Asia and Japan, where the disease was first described in 1899. During World War II, scrub typhus killed or incapacitated thousands of troops who were stationed in rural or jungle areas of the Pacific theatre. The disease is called scrub typhus because it generally occurs after exposure to areas with scrub vegetation because this is where the rodents predominantly live. It has recently been found that the disease can also be prevalent in areas, such as sandy beaches, mountain deserts, and equatorial rain forests.

Rickettsial diseases such as scrub typhus have forced the American military to continue work on countermeasures to control the arthropod vectors and participate in the development of rapid, accurate diagnostic tests, vaccines, and improved surveillance methods.¹

The eMedicine Pediatrics article Scrub Typhus may be helpful. Additionally, the Medscape Emerging and Reemerging Infectious Diseases Resource Center may be of interest.

Pathophysiology

Scrub typhus is caused by Rickettsia tsutsugamushi (Orientia tsutsugamushi). It is a tiny intracellular parasite that lives primarily in mites (the primary reservoir) belonging to the species Leptotrombidium (Trombicula) akamushi and Leptotrombidium deliense. The Rickettsia organisms are found throughout the mite's body, but the highest number is present in the salivary glands. When the mite feeds on rodents (eg, rats, moles, and field mice, which are the secondary reservoirs) or humans, the parasites are transmitted to the host. Only larval Leptotrombidium mites (eg, chiggers) transmit the disease. This zoonotic disease may disseminate into multiple organs through endothelial cells and macrophages, resulting in the development of fatal complications.^{2, 3}

Frequency

United States

The United States is not affected by scrub typhus. The only cases of scrub typhus in the United States are in travelers who have recently been to one of the endemic areas.

International

The disease is limited to eastern and southeastern Asia, India, and northern Australia and the adjacent islands. The seasonal occurrence of scrub typhus varies with the climate in different countries because the mites are able to thrive as conditions change. The mites prefer the rainy season and certain areas (eg, forest clearings, riverbanks, grassy regions). Areas in which the mites thrive pose a greater risk to humans. The prevalence of scrub typhus in Japan has been rising, and much of the current research has been based in Japan.

Mortality/Morbidity

The mortality rate ranges from 1-60%, depending on the geographic area and the rickettsial strain.

• Death can occur from the primary infection or from secondary complications (eg, pneumonitis, encephalitis, circulatory failure).
• Most fatalities occur by the end of the second week of infection.

Race

All races are affected equally.

Sex

Both men and women are affected equally.

Age

People of all ages are affected equally.

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