Scrub Typhus

Scrub typhus (also referred to as bush typhus or tsutsugamushi disease) is an infection caused by Orientia tsutsugamushi, a Gram-negative α-proteobacterium within the family Rickettsiaceae that is now placed in its own genus, Orientia, rather than with the typhus rickettsiae proper ^[1]. The organism is an obligate intracellular parasite transmitted to humans through the bite of infected trombiculid mites, establishing it as a mite-borne zoonosis with rodent reservoirs ^[1][3].

The illness typically begins as a non-specific acute febrile syndrome with headache, myalgia, cough, and constitutional complaints, and the spectrum ranges from subclinical infection through organ failure to fatal disease ^[1][3]. Characteristic physical findings include a morbilliform rash, a pathognomonic black eschar at the site of the mite bite, splenomegaly, and lymphadenopathy, while early laboratory features commonly show leukopenia and abnormal liver function tests ^[1]. More virulent strains may produce hemorrhage and intravascular coagulation, and late-phase complications include pneumonitis, encephalitis (with scrub typhus identified as a leading cause of acute encephalitis syndrome in some Indian states such as Bihar), and myocarditis ^[1].

Scrub typhus is endemic across a broad Asia-Pacific region known as the tsutsugamushi triangle, extending from northern Japan and far-eastern Russia in the north, south to the Solomon Sea and northern Australia, and west to Pakistan and Afghanistan ^[1]. Globally it is considered a serious public-health problem in the Asia-Pacific area, threatening an estimated one billion people and causing illness in about one million people each year, with sporadic epidemiologic data still reflecting significant knowledge gaps ^[2]. The disease is also widespread across the Pacific Islands and throughout India, where it is regarded as a potentially serious but readily treatable infection that is nevertheless underestimated because of diagnostic difficulty and limited laboratory capacity in many areas ^[1]. Historical context includes severe World War II epidemics among troops in Burma and Ceylon that underscored the disease's presence in undeveloped areas of the Oceania theater, although contemporaneous records often lacked definitive microbiological confirmation ^[1].

Scrub typhus is a vector-borne zoonosis transmitted by the larval stage of trombiculid mites—commonly called chiggers and most notably Leptotrombidium deliense—which inhabit areas of dense scrub vegetation ^[1]. The mites feed on infected rodent reservoir hosts and subsequently transmit O. tsutsugamushi to other rodents and to humans through their bites, with the bite site characteristically developing into a black eschar that is diagnostically useful ^[1].

Prevention of scrub typhus is anchored in vector avoidance and reduction of exposure to chigger-infested scrub vegetation, since no broadly effective vaccine had been available historically and short or inadequate antibiotic courses can lead to treatment failure ^[4]. The antigenic heterogeneity of O. tsutsugamushi precludes generic immunity and permits reinfection, which has made prophylaxis a key research priority, with vaccine development regarded as the ultimate long-term goal ^[2][4].

1. 1Wikipedia contributors. Scrub typhus - Wikipedia [Internet]. Wikipedia. cited 3 Sept 2026.Available from: https://en.wikipedia.org/wiki/Scrub_typhus
2. 2Xu G et al. A review of the global epidemiology of scrub typhus. PLoS Negl Trop Dis. 2017 Nov. PMID: 29099844. doi: 10.1371/journal.pntd.0006062.PubMed: https://pubmed.ncbi.nlm.nih.gov/29099844/
3. 3Mahajan SK et al. Scrub typhus. J Assoc Physicians India. 2005 Nov. PMID: 16515236.PubMed: https://pubmed.ncbi.nlm.nih.gov/16515236/
4. 4Twartz JC et al. Scrub typhus 1980. Ann Acad Med Singap. 1981 Jan. PMID: 6792975.PubMed: https://pubmed.ncbi.nlm.nih.gov/6792975/