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Letter
First Documented Human Rickettsia
aeschlimannii Infection
To the Editor: Rickettsia aeschlimannii, which was first
isolated from Hyalomma marginatum ticks collected in Morocco in
1997 (1), has also been found in H. marginatum
ticks from Zimbabwe, Niger, and Mali (2). For the past
3 years, we have included this species in the panel of rickettsiae for
which sera from patients with suspected tickborne diseases are routinely
tested. This procedure allowed us to document, by polymerase chain reaction
(PCR) amplification and serologic testing, the first case of R. aeschlimannii
human infection, which occurred in a patient returning from Morocco.
This 36-year-old man traveled to Morocco in August 2000. On returning
to France, he noticed a vesicular lesion of the ankle, which became necrotic
and resembled the typical “tâche noire” of Mediterranean spotted fever
(3). He became ill with fever of 39.5°C and a generalized
maculopapular skin rash. Laboratory tests showed a normal blood cell count
but moderately increased transaminases. An early serum specimen was tested
to confirm the diagnosis of Mediterranean spotted fever. By microimmunofluorescence,
the patient’s serum had immunoglobulin G and M titers of 1:32 and 1:16,
respectively, against R. aeschlimannii; 0 and 1:16 against R.
conorii, R. africae, R. slovaca, R. helvetica,
and R. massiliae; and 0 and 1:8 against “R. mongolotimonae.”
Western blot results showed that the patient’s serum reacted more intensively
with R. aeschlimannii proteins than with those of the other tested
rickettsiae. Attempted PCR amplification of a 630-nt portion of the rickettsial
ompA gene (nt 70 to 701) (4) from the early serum
specimen yielded a product of the expected size. The sequence of this
amplicon allowed the identification of R. aeschlimannii with 100%
homology. The patient was treated with doxycycline, 200 mg daily for 1
week, and rapidly recovered.
This case is the first documented infection caused by R. aeschlimannii,
a Rickettsia that had been isolated only from Hyalomma marginatum
ticks from Africa. In our patient, its pathogenic role was demonstrated
by PCR, a technique that has also proven useful in identifying other new
rickettsial diseases, including infections with R. helvetica (5),
R. slovaca (6), and R. felis (7).
The serologic findings indicated antibodies at a higher level to R.
aeschlimannii than to other tested species. R. aeschlimannii is
phylogenetically distant from R. conorii but is closely related
to R. rhipicephali and R. montanensis, which have never
been described as human pathogens. This patient appeared to have a typical
case of R. conorii infection, with seasonal and geographic characteristics
favoring this diagnosis (3). This case was clinically
and epidemiologically mistaken for R. conorii infection, suggesting
that R. aeschlimanii may be another cause of Mediterranean spotted
fever in Morocco.
The systematic identification of rickettsial species in human infections
continues to increase the number of recognized human pathogens (3).
This finding has demonstrated once again that more than one species or
serotype of tick-transmitted rickettsia may be prevalent in the same area,
as observed, for example, with R. slovaca, R. mongolotimonae,
and R. conorii in southern France (3); R.
africae and R. conorii in sub-Saharan Africa (8);
and R. conorii and Israeli spotted fever rickettsia in Sicily and
Portugal (9). Rickettsia species first identified
in ticks should be considered as potential human pathogens, as all recently
described tick-transmitted rickettsiae pathogenic for humans were initially
found in ticks and were considered nonpathogenic for several years (3).
Didier Raoult,* Pierre-Edouard Fournier,* Philippe Abboud,† and François
Caron†
*Unité des Rickettsies, Université de la Méditerranée, Marseille,
France; and †Service de Maladies Infectieuses, Centre Hospitalier Universitaire
de Rouen, Rouen, France
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