Rickettsia raoultii in Dermacentor reticulatus Ticks, Chernobyl Exclusion Zone, Ukraine, 2010.

To the Editor: The Chernobyl Exclusion Zone (CEZ) surrounds the center of the 1986 Chernobyl nuclear power plant disaster. Preliminary study shows predominance of Dermacentor reticulatus ticks in the CEZ; ticks of other species, such as Ixodes ricinus, are surprisingly rare, even in habitats where they should be relatively common (). A few reports document presence of Ix. trianguliceps ticks (,). Prevalence of pathogens (Anaplasma phagocytophilum, Borrelia burgdorferi s.l., Babesia spp.) in these ticks is higher in the CEZ than in other regions (,). One pathogen transmitted by Dermacentor spp. ticks is Rickettsia raoultii, which has been isolated from species of Dermacentor ticks found in Asia (,) and since 1999 has also been detected in Europe.

In our study, D. reticulatus ticks were collected by use of the flagging method () in the CEZ in September 2010. Ticks were collected from areas where they were known to occur, around the former villages of Korohod (51°16′02′′N; 30°01′04′′E) and Cherevach (51°12′44′′N; 30°07′45′′E) and around Chernobyl city (51°17′04′′N; 30°13′25′′E). The habitats investigated included open areas and the remnants of farmlands. A total of 201 D. reticulatus ticks, 87 males and 114 females, were collected and investigated (Table).

Table

Prevalence of Rickettsia raoultii infection among Dermacentor reticulatus ticks, Chernobyl Exclusion Zone, Ukraine, 2010

Area of tick collection	No. ticks infected/no. ticks examined (prevalence, %)
	Male	Female	Total
Korohod	40/48 (83.33)	40/60 (66.66)	80/108 (74.07)
Cherevach	21/28 (75.00)	32/46 (69.56)	53/74 (71.62)
Chernobyl	9/11 (81.82)	4/8 (50.00)	13/19 (68.42)
All 3 areas	70/87 (80.46)	76/114 (66.66)	146/201 (72.64)

DNA was extracted by use of the ammonium hydroxide method (). Isolated DNA was examined for the presence of the Rickettsia sp. citrate synthase gene (gltA) by use of PCR with RpCS.409d and RpCS.1258n primers (). Positive amplicons were sequenced, and sequences were edited by using AutoAssembler software (Applied Biosystems, Foster City, CA, USA) and compared with GenBank entries by using blastn version 2.2.13 (http://www.ncbi.nlm.nih.gov/blast/download.shtml). All obtained sequences were submitted to GenBank (accession nos. KX056493 and KX056494).

Infection with Rickettsia spp. was detected in 72.64% of ticks (Table). A higher proportion of males (80.46%) than females (66.66%) were infected. Sequence analysis showed 100% identity with R. raoultii isolated from D. marginatus ticks from China (GenBank accession nos. KU171018.1 and KT261764.1) and D. reticulatus ticks from Poland (KT277489) and Hungary (LC060714.1). In the CEZ, the predominant tick species is D. reticulatus; no D. marginatus ticks have been found in the CEZ (). Thus, in this area, the R. raoultii vector is D. reticulatus ticks.

The prevalence of R. raoultii infection among D. reticulatus ticks (68.42%–74.07%) is significantly higher in the CEZ than in other regions. A previous study found prevalence of A. phagocytophilum infection in the CEZ to be high, mainly associated with Ixodes ticks () and rarely associated with D. reticulatus ticks. The prevalence of Babesia canis infection, also vectored by this tick, was within the usual range (). The reason for prevalence of at least 2 vectored pathogens being higher in D. reticulatus ticks in the CEZ than in other region is not known and needs more study. The prevalence of these pathogens among mammals that inhabit the CEZ is also not known; the influence of radiation on pathogen level has not been studied. The nucleotide sequences of R. raoultii detected in ticks in the CEZ are identical to sequences originating from other regions and deposited in GenBank; the sequences of A. phagocytophilum and B. canis from the CEZ were also similar to those described elsewhere (). If the reason for the higher R. raoultii infection prevalence is radiation, then radiation also influences the ticks—some morphologic abnormalities have been noted on D. reticulatus ticks collected from the CEZ ().

This study confirms presence of R. raoultii in D. reticulatus ticks in the CEZ. The structure of zoonotic foci in the CEZ seems to differ from that in other regions. Confirmation of this hypothesis needs follow-up study of tickborne pathogens in wild mammals that might serve as a source of infection for ticks in the CEZ.