Address for corrrespondence: Prof. Didier Raoult, Unite des Rickettsies, IFR 48, CNRS UMR 6020, Faculté de Médecine, 27 Blvd Jean Moulin, 13385 Marseille, France. Voice: (33) 4.91.32.43.75; fax: (33) 4.91.38.77.72.
Didier.Raoult{at}medicine.univ-mrs.fr.
Ann. N.Y. Acad. Sci. 990: 213-220 (2003).
Rickettsia typhi and
R. felis are flea-transmitted human pathogenic
rickettsial species. To investigate the distributional dynamics
of these rickettsiae we designed a micro-immunofluorescence
assay (MIF) using species-specific monoclonal antibodies (MAbs)
applied to flea cryosections. Our assay was performed in less
than 3 h and its applicability was demonstrated by the detection
of
R. typhi in 50 artificially infected human body lice but
in none of 50 uninfected lice. With MIF, we identified 31 positive
among 32 fleas proven with PCR to be naturally infected with
R. felis; and 7 positive among 32 fleas proven with PCR to be
naturally infected with
R. typhi. No cross-detection was observed
with both MAbs. Fresh
R. felis-infected fleas were significantly
more MIF-positive than long conserved
R. typhi-infected fleas
(31/32 vs. 7/32,
P < 0.01). This discrepancy may be linked
to degradation of antigens by long-term freezing. For
R. typhi-infected
fleas, our assay was significantly more efficient when applied
to fleas in early stages of infection (less than 15 days) by
comparison with fleas frozen more than 20 days after infection
(7/15 vs. 0/17,
P = 0.01). This difference may be related to
an antigenic modification caused by selection pressure in the
vector and host process. The sensitivity of the described method
did not exceed 47% (7/15) for
R. typhi but, in contrast, was
97% for
R. felis. Thus, our method appears to be useful for
surveillance in
R. felis infections, but requires further studies
for the detection of
R. typhi.
