Scrub typhus, also known as bush typhus or mite typhus, is an acute bacterial disease. It can range from mild to severe, becoming life-threatening if untreated. Found primarily in specific regions, understanding it involves recognizing its transmission, signs, and treatments.
What Causes Scrub Typhus and How it Spreads
Scrub typhus is caused by Orientia tsutsugamushi, an obligate intracellular gram-negative bacterium. It transmits to humans through the bite of infected chiggers, the larval stage of trombiculid mites. These tiny larvae, often too small to be seen, feed on skin fluids of hosts like rodents and humans. Mites serve as both vector and natural reservoir for Orientia tsutsugamushi, passing bacteria through generations. When an infected chigger bites a human, bacteria enter the skin and multiply.
Wild rodents like rats, moles, and field mice are common chigger hosts and secondary bacterial reservoirs. Chiggers acquire infection from these animals or through transovarial transmission from infected parent mites. Humans become infected when bitten by larval mites in endemic areas.
Common Symptoms and Complications
Symptoms begin after an incubation period of 6 to 21 days, averaging 10 to 12 days. Initial signs include sudden fever, chills, severe headache, muscle aches, and swollen lymph nodes.
A distinctive sign at the chigger bite site is an eschar. This lesion starts as a reddish bump, forms a blister, and develops into a black, scab-like ulcer with a necrotic center. While characteristic, an eschar may not always be present or easily detectable, especially in darker skin tones.
A macular rash can develop on the trunk, sometimes spreading to the arms and legs, five to eight days into the fever. Other symptoms include cough, gastrointestinal issues, and altered mental status, from confusion to delirium in severe cases. Untreated scrub typhus can lead to serious complications affecting multiple organ systems.
Complications include inflammation of the lungs (pneumonitis), brain (encephalitis), and heart (myocarditis). It can progress to acute kidney failure, circulatory collapse, and disseminated intravascular coagulation (DIC), where blood clots form throughout the body, potentially leading to organ damage and hemorrhage.
Global Distribution and Risk Areas
Scrub typhus is endemic to the “tsutsugamushi triangle,” a broad area encompassing parts of Asia, the Pacific Islands, and northern Australia. Countries in this range include Japan, Korea, China, India, Thailand, Malaysia, Vietnam, and Pakistan.
The disease is prevalent where chigger vectors thrive: rural areas with dense vegetation, scrubland, and forest edges. Chiggers prefer moist, shaded areas with tall grasses and bushes, suitable habitats for rodent hosts.
Infection risk links directly to exposure in these settings. People engaging in outdoor activities like farming, logging, hiking, or military training in endemic regions are at higher risk. Even small, localized patches of suitable vegetation can harbor infected mites, creating “mite islands” or “hot spots” that significantly increase transmission risk.
How Scrub Typhus is Diagnosed and Treated
Diagnosis begins with clinical evaluation, considering symptoms and exposure history in endemic areas. A characteristic eschar, fever, and other typical signs can strongly suggest the disease. However, non-specific early symptoms often require laboratory confirmation.
Confirmatory laboratory tests involve serological assays, detecting antibodies to Orientia tsutsugamushi. Common tests include indirect immunofluorescence assay (IFA) and enzyme-linked immunosorbent assay (ELISA). PCR tests can also detect bacterial DNA in patient samples, especially in early stages.
Antibiotic therapy treats scrub typhus. Doxycycline is the preferred antibiotic for all age groups, including children, and is highly effective. Doxycycline treatment leads to rapid symptom improvement, often within 36 hours. Other antibiotics, like azithromycin or chloramphenicol, may be alternatives in specific situations, such as during pregnancy.
Early diagnosis and prompt antibiotic treatment are important for a favorable outcome and to prevent severe complications. For severe cases, supportive care includes managing fever, hydration, and addressing organ dysfunction. Recovery is prompt with timely and effective treatment.
Preventing Scrub Typhus Infection
Preventing scrub typhus involves minimizing exposure to infected chiggers in endemic areas. Avoid high-risk environments like dense scrubland and heavily vegetated areas, especially during peak chigger activity. If travel is unavoidable, protective clothing offers a barrier.
Wear long-sleeved shirts, long pants tucked into socks or boots, and closed-toe shoes to reduce exposed skin. Treat clothing and gear with permethrin repellents. Apply insect repellents containing DEET (N,N-diethyl-meta-toluamide) to exposed skin for protection against chigger bites.
After time in potentially infested areas, check clothing and skin for chiggers and remove them promptly. Showering and washing clothes can dislodge attached mites. While environmental control like clearing vegetation may be relevant in localized settings, personal protective measures are most practical.