Scrub Typhus
How do people get scrub typhus?
You can get scrub typhus if you are bitten by a chigger that is infected with
O. tsutsugamushi bacteria. The bacteria are found throughout the body of the chigger; although, the highest concentration is present in the salivary glands. Bacteria are transmitted to the host when an infected chigger feeds on a host (human or other animal).
Do all mites transmit scrub typhus?
 Immature mites only have 6 legs.
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Most human cases of scrub typhus are acquired from
Leptotrombidium akamushi and
L. deliense (or other trombiculid mites depending on the geographic location). Only the larval life stage (chigger) of
Leptotrombidium transmits the disease since the other life stages (nymph and adult) do not feed on vertebrate animals. Small, ground-dwelling mammals like rats, voles, and tree shrews are the primary hosts for chigger mites and are important in the ecology of the bacteria. Leptotrombidium mites act as the primary reservoirs for bacteria
O. tsutsugamushi. Chigger mites become infected by feeding on the blood of infected rodents (especially rats, moles, and mice), and maintain the infection throughout all their life stages, ultimately passing the bacteria to their eggs in process called transovarial transmission. Transovarial transmission lets Leptotrombidium mites maintain the bacteria in their populations over long periods of time. Infected mites feed on rodents, and the rodents become a secondary reservoir host that can infect other uninfected mites.
How common is scrub typhus?
Scrub typhus is present in southeastern Asia, including Pakistan, Afghanistan, Korea, Thailand, Japan, and the Philippines. It can also be found in eastern China and southeastern Russia, India, northern Australia, Indonesia, and the islands of the southwestern Pacific. While scrub typhus does not occur in the United States, it is sometimes diagnosed in travelers who have visited the before-mentioned countries. Disease transmission is usually caused by small “pockets” of infected chigger mites, known as “mite islands” or “typhus islands,” and these pockets can persist for years. Infected mites have been found in sites as varied as subarctic regions, seashores, mountains up to 10,000 feet, rain forests, river banks, semiarid deserts, rice paddies, and urban areas. Scrub typhus was first described in Japan in 1899. During World War II, scrub typhus killed or incapacitated thousands of troops fighting in rural or jungle areas of the Pacific theater (5,441 cases with 283 deaths among U.S. Army personnel). It is the suspected leading cause of fevers of unknown origin in U.S. Forces during the Vietnam conflict and caused two confirmed cases among U.S. troops during the Korean War. Two outbreaks of scrub typhus occurred among U.S. Marines training at Camp Fuji, Japan in 2000 and 2001.
What are the symptoms of scrub typhus?
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Typical eschar of scrub typhus located at chigger bite.
| Secondary spotted rash of scrub typhus.
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Symptoms usually begin suddenly 6‒21 days after the bite of an infected chigger. Initial symptoms can include moderate to high fever, severe headache, shaking, chills, cough, body aches, muscle pain, conjunctivitis (inflammation of the mucous membranes lining the eyes), rash, mental changes (ranging from confusion to coma), and swollen lymph nodes. A small (0.5 inch), flat ulcer forms at the bite site. Within a few days, the ulcer swells, fills with fluid, and ruptures, finally forming a black scab (called an eschar). Scarring may result. A red-spotted rash may appear on the torso and extend over the arms and legs in the first week after the bite. The rash can remain flat and fade away within a few days or become raised and intensely colored. If untreated, scrub typhus can also cause an enlarged spleen, lung infection (especially pneumonia), heart muscle inflammation, increased pulse rate, severe drop in blood pressure, delirium, loss of consciousness, and death by the end of the second week. In the most severe cases, untreated scrub typhus may kill up to 60% of infected people, though the death rate is highest for the elderly and those with compromised immune systems. Previous infections may provide some immunity to reinfection with scrub typhus.
How is scrub typhus diagnosed?
See your healthcare provider if you develop the symptoms listed above after spending time in areas where scrub typhus is found. Blood tests and physical symptoms are used to diagnose scrub typhus. Your healthcare provider may order blood tests to look for scrub typhus or other diseases.
What can I do to reduce my risk of becoming infected
with scrub typhus?
- Wear proper clothing as a physical barrier against chiggers—long pants tucked into boots or tightly-woven socks, long sleeve shirt, and shirt tucked into pants. Avoid walking barefoot. and do not wear open-toed shoes or sandals.
- When travelling to places where scrub typhus is common, avoid areas with lots of vegetation and brush where chiggers may be found. Stay in the middle of the trail and avoid grass and shrubs.
- Do not sit or lay down on bare ground, grass, or other vegetation. Always use a ground cover, preferably one that has been treated with permethrin repellent.
- Clear scrubby vegetation and keep grass short. Control chiggers with EPA-registered pesticides when other methods fail.
- Keep rodents and other animals out of camping and bivouac areas. Practice good food hygiene to discourage rodents that may be carrying mites.
- When possible, shower immediately after you have been in chigger habitat. Scrub your skin to help remove any attached chiggers.
- Launder your uniform and clothing regularly.
- The best way to scrub typhus is to protect yourself from mites by using the DoD Insect Repellent System. It incorporates insect repellent on the uniform, DEET, picaridin, or IR3535 repellent on exposed skin, a properly worn uniform, and sleeping inside a insecticide-treated bed net.
Select the image for more information on the DoD Insect Repellent System.
