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Letter
Rickettsiae
in Ixodid Ticks, Sicily
Tiziana Beninati,*
Claudio Genchi,* Alessandra Torina,† Santo Caracappa,† Claudio Bandi,*
and Nathan Lo*
*Universita' degli Studi di Milano, Milano, Italy; and †Istituto Zooprofilattico
della Sicilia, Palermo, Italy
Suggested
citation for this article
To the Editor: Members of the spotted fever group rickettsiae
are intracellular bacteria usually associated with ixodid ticks, which
are transferred to vertebrates by salivary secretions and within ticks
transtadially and transovarially. Several tickborne rickettsiae cause
human or animal diseases and, in the last 10 years, the increased use
of molecular-based identification methods has resulted in new spotted
fever group rickettsiae being characterized in ixodid ticks throughout
Europe (1). Until recently, no rickettsiae, other than
Rickettsia conorii, were reported in Italy. Since 2002, R. helvetica
and Israeli spotted fever Rickettsia (R. conorii complex)
have been detected in Ixodes ricinus and Rhipicephalus sanguineus,
respectively (2–4). In Italy, Mediterranean spotted fever
is endemic. This disease appears to occur more commonly in some central
and southern regions (5); in 2002, more than half (498
of 890) of the cases of Mediterranean spotted fever identified in Italy
and reported to the Ministry of Health came from Sicily.
Because of the relatively high prevalence of rickettsial diseases in
southern regions, we analyzed tick samples collected during 2001 and 2002
from herbivores (bovines, ovines, donkeys) from Sicilian farms in Corleone
(Palermo Province) to determine the diversity of spotted fever group rickettsiae
in various ixodid tick species. DNA from 238 tick samples from various
genera (Dermacentor, Rhipicephalus, Hyalomma, Haemaphysalis,
Ixodes) was extracted; in some cases, individual ticks of the same
species collected from the same animal were pooled. Polymerase chain reaction
screening and sequencing with primers for the gene encoding the cell surface
antigen (sca4) (previously known as "gene D") and the
17-kDa antigen gene were performed as previously reported (6,7).
A total of 7 positives were found, and the sequences obtained were compared
to other bacterial sequences present in the GenBank database (Table).
A 469-bp fragment with 100% identity to the R. slovaca sca4 sequence
(AF155054) was obtained from 2 Dermacentor marginatus and 1 Haemaphysalis
punctata. A 403-bp fragment with 99.75% identity (1-bp difference)
to the sca4 sequence from R. africae (AF151724) was found
from 1 Hyalomma marginatum, and a 423-bp fragment with 100% similarity
to R. conorii sca4 sequence (AE008626) was found from Rhipicephalus
turanicus. Finally, a 489-bp fragment with 99.79% identity (1-bp difference)
to R. aeschlimannii sca4 sequence (AF163006) was obtained from
2 H. marginatum samples. The levels of identity between the 17-kDa
antigen sequences (ranging in length from 351 to 419 bp) obtained during
this study and those in GenBank were generally lower than those for sca4
because the 17-kDa antigen gene has not been sequenced for most of the
Rickettsia spp. identified here on the basis of sca4 sequences.
One exception was the fragment obtained from the Rh. turanicus
sample, which had 100% identity with the R. conorii 17-kDa antigen
sequence (AE008675). All sca4 and 17-kDa antigen gene sequences
described in this study have been deposited in the EMBL database (accession
no. AJ781411–AJ781420).
Among the numerous rickettsia species recently described in Europe,
R. africae and R. slovaca are known as human pathogens (8),
and the first case of R. aeschlimannii infection in humans has
recently been reported (9). African tick bite fever caused
by R. africae is known as an imported disease in patients returning
from sub-Saharan Africa or the West Indies (8), but our
report raises the possibility that the rickettsial agent is actually present
in European ticks from genera other than Amblyomma. R. slovaca
has been shown to be responsible for a human disease known as tick-borne
lymphadenopathy (10). Considering the problem of cross-reaction
between different spotted fever group rickettsiae during serologic tests,
our findings underscore the importance of using antigens from other spotted
fever group rickettsiae, in addition to that of R. conorii, to
obtain a more specific diagnosis of rickettsioses in Italy (10).
Considering the large number of tick species present in Italy, and their
infection with different spotted fever group rickettsiae, identifying
the tick species responsible for a bite could be helpful for accurate
diagnosis.
Acknowledgments
This work was funded
by the Istituto Zooprofilattico della Sicilia "A. Mirri."
Nathan Lo was supported
by Ministry of Education, University and Research of the Italian government.
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Table. Identification
of Rickettsia spp. in tick samples from herbivores, Corleone
(Palermo Province), Italy, 2001-2002
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No. of ticks infected/total no.
of ticks examined (tick species)
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Minimum-maximum
infection rate (%)
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Rickettsia spp. identified
(% identity with sca4 of spotted
fever group rickettsiae)
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Dermacentor marginatus (2/7)
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28.5
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R. slovaca (100)
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Haemaphysalis punctata (1/15)
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6.6
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R. slovaca (100)
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Hyalomma marginatum (2*/24)
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8.3–20.8
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R. aeschlimannii (99.79)
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Hyalomma marginatum (1/24)
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4.1
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R. africae (99.75)
Rickettsia sp. strain S (99.25)
R. honei (99.0)
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Rhipicephalus turanicus (1†/52)
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1.9–7.6
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R. conorii (100)
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*Two pools of 2 and 3 ticks were positive.
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†One pool of 4 ticks was positive.
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Suggested citation
for this article:
Beninati T, Genchi
C, Torina A, Caracappa S, Bandi C, Lo N.Rickettsiae in ixodid ticks, Sicily
[letter]. Emerg Infect Dis [serial on the Internet] 2005 Mar [date
cited]. Available from http://www.cdc.gov/ncidod/EID/vol11no03/04-0812.htm
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