Tropical rickettsioses
Introduction
Rickettsioses (also called typhus) are infectious diseases caused by obligate intracellular bacteria of the order Rickettsiales.1, 2 These organisms have long been described simply as short, Gram-negative rods that retain basic fuchsin when stained by the method of Gimenez. In recent years, however, the rickettsial field has undergone a significant evolution due to technological advances in molecular genetics and genomics. The taxonomy of rickettsiae has been reorganized and continues to be modified as new data become available.2 Four groups of diseases, however, are still commonly called rickettsioses: (1) diseases due to bacteria of the genus Rickettsia including the spotted fever group and the typhus group of the family Rickettsiaceae, (2) scrub typhus due to Orientia tsutsugamushi (formerly named R tsutsugamushi), (3) human ehrlichioses and anaplasmosis due to bacteria within the family Anaplasmataceae, and (4) the ubiquitous Q fever due to Coxiella burnetii, which was, however, recently removed from the Rickettsiales. Here, we review tropical rickettsioses, focusing on clinical and epidemiologic aspects and management. The reader is therefore referred to recent reviews of ehrlichioses and anaplasmosis (which have not been properly demonstrated to occur in the tropics)3, 4 and Q fever.5
Section snippets
Exposure
The agents of tropical rickettsioses are associated with arthropods including ticks, mites, fleas, and lice, which may act as vectors, reservoirs, and/or amplifiers of the bacteria.1, 3 Thus, exposure to the disease is closely linked to exposure to the arthropod vectors. Most of them favor specific optimal environmental conditions, biotopes, and hosts. These factors determine the geographic repartition of the vector and consequently the risk area for the diseases. This is particularly true when
Tick-borne spotted fever group rickettsioses
Tick-borne rickettsioses are among the oldest known vector-borne diseases. Both Rocky Mountain spotted fever (RMSF) due to R rickettsii and Mediterranean spotted fever (MSF) due to R conorii conorii have been described since the beginning of the 20th century. During most of the 20th century, the epidemiology of tick-borne rickettsioses could be summarized as the occurrence of a single pathogenic Rickettsia on each continent, with the addition of R sibirica (in the former USSR and China) and R
Flea-borne murine typhus
Murine typhus (also called endemic typhus) is one of the oldest recognized arthropod-borne zoonoses. It was probably reported in Mexico in 1570 by Bravo and described clinically in grain silo workers in Australia in 1923. The disease was recognized to be distinct from epidemic typhus in the 1920s and the causative organism named R mooseri and, thereafter, R typhi. It is a Gram-negative obligate intracellular bacterium belonging to the typhus group of the genus Rickettsia.1
The main vector of
Louse-borne rickettsiosis: epidemic typhus
Epidemic typhus is caused by R prowazekii, a typhus group Rickettsia whose entire genome has been sequenced, and it is considered one of several prototypical reduced genome bacteria.30 The disease is suspected to have been responsible for the āAthenian plagueā in the fifth century bc. Typhus was apparently widespread in Italy during the 16th century, a period when war ravaged both France and Spain.
Huxham first made the distinction between the typhus and typhoid in 1739. Boissier de Sauvages
Scrub typhus
Orientia tsutsugamushi (formerly named R tsutsugamushi) is the agent of scrub typhus. These bacteria had been classified for a long time in the order Rickettsiales. In the recent years, however, with the advent of molecular taxonomic methods in phylogenetic studies, the position of R tsutsugamushi has been shown to be sufficiently distinct to justify the creation of a new genus, Orientia.40 Orientia tsutsugamushi has enormous genetic and antigenic variability, but seems genetically stable.24
Routine laboratory investigation
Routine laboratory abnormalities in rickettsioses include leukocyte count abnormalities, anemia, thrombocytopenia, hyponatremia, hypoalbuminemia, and hepatic and renal abnormalities. In an attempt to distinguish between scrub typhus and dengue in HIV-negative patients presenting with fever of unclear etiology from northern Thailand, Watt et al51 identified three features that were found to be more common in dengue as compared with scrub typhus: bleeding from the gums, a low platelet count, and
Management of tropical rickettsioses
Empirical treatment of rickettsioses is usually initiated before laboratory confirmation of the diagnosis, which is seldom available in most tropical settings.
Doxycycline remains the treatment of choice for all rickettsioses and for all patients, including young children, with potentially life-threatening rickettsioses such as RMSF.2 In general, the risk of dental staining by doxycycline is negligible when a single, relatively short (eg, 5-10 days) course of therapy is administered. Parenteral
Prevention
Currently, there are no vaccines against scrub typhus and other tropical rickettsioses. Prevention is therefore based on avoiding contact with the arthropod vector. Topical DEET (N,N-diethyl-m-toluamide) applied to exposed skin will prevent tick, flea, and chigger bite. Furthermore, clothing (or army uniforms) should be treated with permethrin that is neurotoxic to insects and has āknockdownā capability, killing arthropods on contact.66, 67, 68 Once applied, permethrin is stable through a
Conclusions
In conclusion, little is known about the rickettsioses in the tropics. Much of the recent information on the epidemiology and clinical particularities of the diseases have been obtained in first-world laboratories that promote international co-operation with tropical countries. Recent data on the clinical aspects of the diseases have been derived from infected visitors returning from the tropics. An increase in persons traveling to tropical climates to participate in recreational activities
References (68)
- et al.
Natural history and pathophysiology of Q fever
Lancet Infect Dis
(2005) - et al.
Rickettsia felis rickettsiosis in Yucatan
Lancet
(2000) Rickettsialpox
Dermatol Clin
(1997)- et al.
Tick-borne rickettsioses in international travellers
Int J Infect Dis
(2004) - et al.
Clinical and laboratory features of murine typhus in central Tunisia: a report of seven cases
Int J Infect Dis
(2005) - et al.
Murine typhus in Greece: epidemiological, clinical, and therapeutic data from 83 cases
Trans R Soc Trop Med Hyg
(2002) - et al.
Some lessons from Rickettsia genomics
FEMS Microbiol Rev
(2005) - et al.
The history of epidemic typhus
Infect Dis Clin North Am
(2004) - et al.
Outbreak of epidemic typhus associated with trench fever in Burundi
Lancet
(1998) Drug-resistant scrub typhus: paradigm and paradox
Parasitol Today
(1997)
HIV-1 suppression during acute scrub-typhus infection
Lancet
Scrub typhus infections poorly responsive to antibiotics in northern Thailand
Lancet
Medical pearl: permethrin can prevent arthropod bites and stings
J Am Acad Dermatol
Prevention of arthropod-related disease
J Am Acad Dermatol
Rickettsioses as paradigms of new or emerging infectious diseases
Clin Microbiol Rev
Tick-borne rickettsioses around the world: emerging diseases challenging old concepts
Clin Microbiol Rev
Tick- and flea-borne rickettsial emerging zoonoses
Vet Res
Ehrlichia chaffeensis: a prototypical emerging pathogen
Clin Microbiol Rev
Ticks and tickborne bacterial diseases in humans: an emerging infectious threat
Clin Infect Dis
African tick bite fever in travelers to rural sub-Equatorial Africa
Clin Infect Dis
Rickettsia parkeri: a newly recognized cause of spotted fever rickettsiosis in the United States
Clin Infect Dis
Rickettsia parkeri and other spotted fever infections in the United States
N Engl J Med
Beitrage zur Kenntnis der Rickettsien
Arch f Schiffs und Tropenhyg Liepzig
Amended description of Rickettsia felis (Bouyer et al. 2001), a temperature-dependent cultured bacterium
Int J Syst Evol Microbiol
The genome sequence of Rickettsia felis identifies the first putative conjugative plasmid in an obligate intracellular parasite
PLoS Biol
A flea-associated Rickettsia pathogenic for humans
Emerg Infect Dis
Rickettsia felis infection acquired in Europe and documented by polymerase chain reaction
Emerg Infect Dis
First molecular detection of Rickettsia felis in fleas from Algeria
Am J Trop Med Hyg
Detection of Rickettsia felis in a New World flea species, Anomiopsyllus nudata (Siphonaptera: Ctenophthalmidae)
J Med Entomol
Flea-borne rickettsioses: ecologic considerations
Emerg Infect Dis
Rickettsialpox in New York City: a persistent urban zoonosis
Ann NY Acad Sci
Rickettsialpox in Turkey
Emerg Infect Dis
Reemerging murine typhus Japan
Emerg Infect Dis
Murine typhus in travelers returning from Indonesia
Emerg Infect Dis
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