Rickettsia aeschlimannii: a new pathogenic spotted fever group Rickettsia, South Africa. (Letters).
To the Editor: Spotted fever group rickettsiae are increasingly recognized as agents of disease in residents of and tourists to South Africa (1). To date, two species, Rickettsia rickettsia (rĭkĕt`sēə), any of a group of very small microorganisms, many disease-causing, that live in vertebrates and are transmitted by bloodsucking parasitic arthropods such as fleas, lice (see louse), and ticks. . conorii and R. africae, which cause Mediterranean spotted fever (MSF) and African tick-bite fever (ATBF ATBF Adipose Tissue Blood Flow
ATBF Australasian Tissue Banking Forum
ATBF Asian Tchoukball Federation ), respectively, have been associated with human disease in the region; ATBF is more frequently associated with travel (1). As different antibiotic regimens are recommended for the two syndromes, differentiating MSF from ATBF is important. Increasing evidence shows that the syndromes can usually be differentiated through clinical manifestations and epidemiologic characteristics (1).
We recently encountered a South African patient who, on returning from a hunting and fishing trip, discovered a Rhipicephalus appendiculatus tick attached to his right thigh and an eschar eschar /es·char/ (es´kahr)
1. a slough produced by a thermal burn, by a corrosive application, or by gangrene.
2. tache noire.
n. around the attachment site. The patient was aware of the risk of tick-transmitted disease; after removing the tick, immediately self-prescribed doxycycline doxycycline /doxy·cy·cline/ (dok?se-si´klen) a semisynthetic broad-spectrum tetracycline antibiotic, active against a wide range of gram-positive and gram-negative organisms; used also as d. calcium and d. hyclate. . No further symptoms developed. However, as a precaution, the patient went to a local clinic, where a skin biopsy was taken from the eschar. This sample, together with the removed tick, was submitted to our laboratory. DNA DNA: see nucleic acid.
or deoxyribonucleic acid
One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes. extracts, prepared from an eschar biopsy and the tick, were incorporated into a polymerase chain reaction polymerase chain reaction (pŏl`ĭmərās') (PCR), laboratory process in which a particular DNA segment from a mixture of DNA chains is rapidly replicated, producing a large, readily analyzed sample of a piece of DNA; the process is (PCR PCR polymerase chain reaction.
polymerase chain reaction
Polymerase chain reaction (PCR) ) assay specifically targeting a fragment of the rickettsial rickettsial /rick·ett·si·al/ (ri-ket´se-al) pertaining to or caused by rickettsiae.
Relating to, or caused by a member of the genus Rickettsia. ompA (2). Sequence analysis of the amplification products showed both to be identical and to share >99% similarity with the ompA of R. aeschlimannii, a species not previously associated with human disease. Unfortunately, blood samples could not be collected at the time the patients first had symptoms; thus, investigation of a disseminated infection by PCR and serologic testing was not possible.
Although genotypically indistinguishable organisms had previously been detected in Hyalomma marginatum collected in Portugal and Zimbabwe, R. aeschlimannii was first characterized following its isolation from H. marginatum ticks in Morocco (3) and recently in Niger (4). This encounter was the first demonstration of its presence in South Africa and in Rhipicephalus ticks.
A lack of suitable clinical material prevented full evaluation of the pathogenic potential of R. aeschlimannii in this patient and prompt antibiotic intervention may have prevented evolution of the syndrome. Nonetheless, that R. aeschlimannii was transmitted to the patient and established a local infection leading to eschar formation provides clear, albeit preliminary, evidence of its virulence. Until further cases are encountered, allowing better characterization of the clinical manifestations associated with R. aeschlimannii infection and considering the agent capable of inducing either MSF or ATBF-like manifestations is crucial; neither of these syndromes can be associated with a specific causative agent without microbiologic identification. Our findings demonstrate that Rickettsia species first encountered in tick surveys are associated with human disease, and we should not assume that some Rickettsia species not have a pathogenic potential.
(1.) Raoult D, Fournier P-E, Fenollar F, Jensenius M, Prioe T, De Pina JJ, et al. Rickettsia africae, a tick-borne pathogen of travelers to sub-Saharan Africa. N Engl J Med 2001;344:1504-10.
(2.) Roux V, Fournier P-E, Raoult D. Differentiation of spotted fever group rickettsiae by sequencing and analysis of restriction fragment length polymorphism restriction fragment length polymorphism
n. Abbr. RFLP
Intraspecies variations in the length of DNA fragments generated by the action of restriction enzymes and caused by mutations that alter the sites at which these enzymes act, changing of PCR amplified DNA of the gene encoding the protein rOmpA. J Clin Microbiol 1996;34:2058-65.
(3.) Beati L, Meskini M, Thiers B, Raoult D. Rickettsia aeschlimannii sp. nov., a new spotted fever group rickettsia associated with Hyalomma marginatum ticks. Int J Syst Bacteriol 1997;47:548-54.
(4.) Parola P, Inokuma H, Camicas J-L, Brouqui P, Raoult D. Detection and identification of spotted fever group rickettsiae and ehrlichiae in African ticks. Emerg Infect Dis 2001;7:1014-7.
Anne-Marie Pretorius * and Richard J. Birtles ([dagger])
* University of the Free State The University of the Free State is situated in Bloemfontein, the capital of the Free State Province, South Africa. Bloemfontein is a modern city offering a full range of recreational, commercial and educational facilities, but which also retains a laid-back atmosphere that , Bloemfontein, South Africa and ([dagger]) University of Liverpool The University of Liverpool is a university in the city of Liverpool, England. History
The University was established in 1881 as University College Liverpool, admitting its first students in 1882. , Liverpool, England