What is scrub typhus?

Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi — an obligate intracellular bacterium transmitted by infected larval mites (chiggers, Leptotrombidium species) during feeding. It is the most common rickettsial infection globally, affecting approximately 1 million people per year in the tsutsugamushi triangle — the Asia-Pacific region from Japan through Southeast Asia to Australia and west to Pakistan. Without treatment, scrub typhus can cause multi-organ failure and death.

What are the symptoms?

Incubation: 6-21 days after mite bite. Sudden onset: fever (often very high — 39-41°C), severe headache, myalgia, malaise — resembling influenza. Rash: maculopapular rash on trunk (days 5-8) — present in approximately 50% but may be subtle in darker skin. Eschar: the pathognomonic finding — a painless black ulcer at the bite site (present in 50-80%); systematically searching all skin surfaces is essential. Lymphadenopathy: regional and sometimes generalised. Severe/untreated: pneumonitis (cough, dyspnoea), meningoencephalitis, acute kidney injury, hepatitis, myocarditis, ARDS.

How is scrub typhus diagnosed?

Clinical diagnosis is key — fever + eschar + travel to or residence in endemic area = empirical treatment with doxycycline without waiting for laboratory confirmation. Laboratory tests: Weil-Felix reaction (OX-K agglutination — the traditional test; low sensitivity/specificity, but widely available). Serological tests: IFA (immunofluorescence assay — gold standard but not universally available); ELISA. PCR (blood or eschar swab) — most sensitive, but requires molecular laboratory. Given the diagnostic limitations and treatability, empirical doxycycline is recommended for clinically compatible cases even without laboratory confirmation.

How does scrub typhus cause such severe disease?

O. tsutsugamushi infects vascular endothelial cells and macrophages — causing vasculitis (blood vessel inflammation) throughout the body. This generalised vasculitis underlies all of scrub typhus's complications: pneumonitis (pulmonary vasculitis and permeability); meningoencephalitis (cerebral vasculitis); acute kidney injury; hepatitis; myocarditis; and potentially ARDS. The wide tissue distribution explains the multi-system nature of scrub typhus — and why untreated disease can be fatal even when the acute bacteraemia appears controlled.

Anyone in the tsutsugamushi triangle exposed to habitats where Leptotrombidium mites are found — particularly transitional vegetation zones (scrub, grassland edges, secondary forest, rice field margins). High-risk activities: walking through tall grass; agricultural work; military field operations; hiking/trekking; camping. Seasonal risk: in many areas, cases peak during the wet season when mite larvae are most abundant.

How can scrub typhus be prevented?

Personal protective measures: insect repellents (DEET on skin; permethrin on clothing); long-sleeved shirts tucked into trousers; tucking trousers into socks; regular body checks for mites (though chigger larvae are tiny, approximately 0.2mm, and difficult to see); bathing and changing clothes after outdoor activity (larvae may not embed immediately). Avoiding high-risk habitats when possible. No vaccine is available. Post-exposure prophylaxis with doxycycline (200mg weekly) can prevent scrub typhus in high-risk exposure situations (military use).

How does GMJ News cover scrub typhus?

GMJ News covers WHO scrub typhus data, eschar recognition, doxycycline efficacy, expanding geographic range including Africa and Middle East, and differential diagnosis from dengue and other febrile illnesses. Scrub typhus represents the broader category of tick- and mite-borne diseases relevant to infectious disease differential diagnosis in travellers and returning workers from Asia-Pacific.

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Scrub Typhus

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Scrub typhus — caused by Orientia tsutsugamushi and transmitted by infected larval mites (chiggers) — is the most common rickettsial infection globally, causing approximately 1 million cases per year in the Asia-Pacific region (the “tsutsugamushi triangle” from Japan to Australia to Pakistan), yet remains severely neglected and underdiagnosed despite being potentially fatal without treatment (WHO). The eschar — a painless black ulcer at the mite bite site — is pathognomonic when present (but found in only 50-80% of cases) and a key diagnostic clue. Doxycycline is the treatment of choice and is highly effective when started early; delayed diagnosis carries significant mortality.

Key messages

1 million cases/year — most common rickettsial infection

Scrub typhus is the most common rickettsial infection globally — causing approximately 1 million cases per year in the tsutsugamushi triangle (a vast Asia-Pacific region from Russia through Asia to Australia/Pacific). It is massively underdiagnosed and potentially fatal without treatment (WHO).

The eschar — the diagnostic clue

The eschar — a painless, black ulcer with a punched-out appearance at the mite bite site — is pathognomonic for scrub typhus. It represents a healing necrotic ulcer from Orientia tsutsugamushi replication at the inoculation site. Found in 50-80% of cases; actively searching for it is essential.

Doxycycline is curative

Doxycycline (100mg twice daily for 7-14 days) is highly effective for scrub typhus — fever typically resolves within 24-48 hours ("doxycycline test"). Azithromycin is the alternative for pregnancy and doxycycline-intolerant patients.

Potentially fatal — multi-organ failure

Untreated or delayed scrub typhus causes multi-organ involvement: pneumonitis, meningoencephalitis, acute kidney injury, hepatitis, myocarditis and ARDS — with case fatality 0-30% depending on the region, strain and treatment access.

Expanding beyond tsutsugamushi triangle

Scrub typhus — previously thought confined to Asia-Pacific — has been documented in the Middle East, East Africa and Northern Africa, reflecting either true geographic spread or improved recognition. Orientia chuto (Africa) is distinct from the Asian Orientia tsutsugamushi.

No vaccine available

Despite decades of research effort, no vaccine is available for scrub typhus — partly because the major surface antigen TSA56 shows enormous antigenic diversity between strains and geographic regions.

Key statistics

~1M

scrub typhus cases/year in tsutsugamushi triangle

WHO/Lancet ID

1B+

people at risk in the tsutsugamushi triangle

WHO

0-30%

case fatality rate without treatment (varies by region/strain)

WHO

50-80%

of cases have identifiable eschar

WHO

24-48hr

time to fever defervescence with doxycycline

WHO/Clinical

approved vaccines for scrub typhus

WHO 2024

Scrub typhus — geographic distribution of cases (tsutsugamushi triangle)

Source: WHO. India, Thailand, China, Indonesia and Japan report the highest burdens.

Glossary of key terms

Orientia tsutsugamushi
WHOAn obligate intracellular bacterium — distinct from Rickettsia species (different genus). Transmitted by larval mites (chiggers) of the genus Leptotrombidium. Enormous antigenic diversity (many strains) — which has frustrated vaccine development.

Chigger mite (Leptotrombidium)
WHOLarval mites of the genus Leptotrombidium — the vector of scrub typhus. Only the larval stage feeds on vertebrate hosts (including humans); nymphs and adults feed on soil organisms. After feeding on an infected host, larvae become infected and transmit to the next vertebrate host they feed on. The "scrub" in scrub typhus refers to the transitional vegetation habitat favoured by Leptotrombidium.

Eschar
WHO/ClinicalA painless, black necrotic ulcer at the site of the Leptotrombidium mite bite — formed by Orientia tsutsugamushi replication in local cells causing local necrosis. Typically 0.5-1cm, with a black central crust surrounded by erythema and induration. Found in 50-80% of cases — systematically searching (axillae, groins, waist, back of knees, hairline, behind ears) increases detection rate.

Doxycycline test
WHO/ClinicalThe rapid defervescence (fever clearance within 24-48 hours) following the start of doxycycline is diagnostically helpful in areas where laboratory confirmation is unavailable — its specificity for rickettsial disease (including scrub typhus) distinguishes it from most other febrile illnesses which respond more slowly to antibiotics.

Tsutsugamushi triangle
WHOThe geographic region where scrub typhus is endemic — bounded by Japan (northeast), Australia (south) and Pakistan/Afghanistan (northwest). This vast area contains approximately 1 billion people at risk. The name comes from the Japanese (tsutsuga = dangerous/noxious; mushi = insect), referring to the chigger vector.

Orientia chuto (Africa)
ResearchA phylogenetically distinct Orientia species — causing scrub typhus-like illness in parts of Africa (documented in Middle East, East Africa and North Africa). Initially called the "Candidatus Orientia chuto" after the area of first discovery in Dubai. Extends the recognised geographic range of scrub typhus beyond the classic tsutsugamushi triangle.

Latest GMJ coverage

Scrub Typhus Diagnosis in India: New Evidence on Serological Testing Accuracy

11/07/2026

Scrub Typhus

Key messages

Key statistics

Glossary of key terms

Latest GMJ coverage

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