Recent developments in molecular taxonomic methods have led to a reclassification of rickettsial diseases. The agent responsible for scrub typhus (Orientia tsutsugamushi) has been removed from the genus Rickettsia and a bewildering array of new rickettsial pathogens have been described. An update of recent research findings is therefore particularly timely for the nonspecialist physician.
An estimated one billion people are at risk for scrub typhus and an estimated one million cases occur annually. The disease appears to be re-emerging in Japan, with seasonal transmission. O. tsutsugamushi has evolved a variety of mechanisms to remain viable in its intracellular habitat. Slowing the release of intracellular calcium inhibits apoptosis of macrophages. Subsets of chemokine genes are induced in infected cells, some in response to transcription factor activator protein 1. Cardiac involvement is uncommon and clinical complications are predominantly pulmonary. Serious pneumonitis occurred in 22% of Chinese patients. Dual infections with leptospirosis have been reported. Standardized diagnostic tests are being developed and attempts to improve treatment of women and children are being made. Of the numerous tick-borne rickettsioses identified in recent years, African tick-bite fever appears to be of particular importance to travellers. The newly described flea-borne spotted fever caused by Rickettsia felis may be global in distribution.
Rash and fever in a returning traveler could be rickettsial and presumptive doxycycline treatment can be curative. Recent research findings raise more questions than answers and should stimulate much needed research.
aDepartment of Retrovirology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand, and bUnité des Rickettsies, WHO Collaborative Center for Rickettsial Reference and Research, Faculté de Médecine, Marseille, France
Correspondence to George Watt, MD, DTM&H, Department of Retrovirology, Armed Forces Research Institute of Medical Sciences, 315/6 Rajvithi Road, Bangkok 10400, Thailand Tel: 662 644 6735; fax: 662 246 8908; e-mail: firstname.lastname@example.org