Orientia tsutsugamushi (Scrub Typhus)

History

The earliest clinical reports of possible scrub typhus date back to the Chinese manual Zhouhofang in 313 bc . In 1810 the association of a febrile illness with mite transmission was made in the Niigata Prefecture in Japan, which led to the first clinical definition of tsutsugamushi fever. Historically, the occurrence of scrub typhus was associated with its dominant presence in Asia, in an area defined as the “Tsutsugamushi Triangle,” but emerging reports of Orientia spp. and clinical cases reported from regions in Africa, Europe, and South America suggest a wider global distribution in tropical to subtropical regions ( Fig. 191.1 ). The recent description of confirmed human cases in Chile has led to a paradigm shift in the epidemiology of scrub typhus. Today, scrub typhus is probably the world's most relevant rickettsial disease based on its disease burden, and although the understanding of its global distribution is expanding, the available literature remains limited.

Definition

Scrub typhus is a vector-borne infectious disease caused by the obligate intracellular bacterium Orientia tsutsugamushi. The initial clinical presentation includes nonspecific “flulike” symptoms such as fever, fatigue, frontal headaches, myalgia, cough, restlessness, and insomnia. In many cases an inoculation lesion may appear, termed eschar or “tache noire” ( Fig. 191.2A–B ). However, in areas where scrub typhus is common and the population is regularly exposed, the presence of an eschar may occur less frequently; this is likely due to preexisting cellular immunity against Orientia spp. Similarly, a diffuse, macular or maculopapular skin rash can develop within 3 to 8 days after the onset of fever. Confusion and gastrointestinal symptoms are common, and complications include respiratory and renal failure, meningitis or meningoencephalitis, and, very rarely, disseminated intravascular coagulation. Severe scrub typhus manifested with severe multiorgan failure in up to a third of hospitalized patients in India, with an average 24% mortality rate. In Lao patients with central nervous system (CNS)–related complications, a mortality rate of 14% was observed, and scrub typhus during pregnancy was associated with poor maternal and fetal outcomes (Laos and Thai-Myanmar border), with approximately a third of cases resulting in either abortion or stillbirth. However, to what extent such outcomes depend on the strain of Orientia, immune competence, and genetics of the patient remains to be defined.

In most endemic areas of scrub typhus, the following differential diagnosis for “typhus-like illnesses” should be considered: malaria, murine typhus, dengue, leptospirosis, Q fever, typhoid, melioidosis, and chikungunya fever; malaria and meningitis should always be ruled out first.