|
|
Letter
Rickettsia aeschlimannii:
A New Pathogenic Spotted Fever Group Rickettsia, South Africa
Suggested citation for this article:
Pretorius A-M, Birtles RJ. Rickettsia aeschlimannii: a new pathogenic
spotted fever group rickettsia, South Africa. Emerg Infect Dis [serial
online] 2002 Aug [date cited];8. Available from: URL: http://www.cdc.gov/ncidod/EID/vol8no8/02-0199.htm
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 conorii
and R. africae, which cause Mediterranean spotted fever (MSF) and
African tick-bite fever (ATBF), 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 around the attachment site.
The patient was aware of the risk of tick-transmitted disease; after removing
the tick, immediately self-prescribed doxycycline. 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 extracts, prepared
from an eschar biopsy and the tick, were incorporated into a polymerase
chain reaction (PCR) assay specifically targeting a fragment of the rickettsial
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.
Anne-Marié Pretorius* and Richard J. Birtles†
*University of the Free State, Bloemfontein, South Africa and †University
of Liverpool, Liverpool, England
References
- 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.
- Roux V, Fournier P-E, Raoult D.
Differentiation of spotted fever group rickettsiae by sequencing and
analysis of restriction fragment length polymorphism of PCR amplified
DNA of the gene encoding the protein rOmpA. J Clin Microbiol 1996;34:2058–65.
- 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.
- 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.
|
