Crimean-Congo Hemorrhagic Fever Virus Clades V and VI (Europe 1 and 2) in Ticks in Kosovo, 2012

Abstract

Despite being a small country, Kosovo represents one of the few foci of Crimean-Congo hemorrhagic fever (CCHF) in Europe. The distribution of Kosovar tick vectors and the evolution of CCHF virus in ticks are both as yet unknown. A better description of the extent and the genetic diversity of CCHFV in ticks from endemic settings is essential, in order to be controlled. We investigated the 2012 distribution of Kosovar ticks alongside the prevalence and the phylogeography of tick-derived CCHFV. Hyalomma marginatum dominated in the endemic municipalities with 90.2% versus 24.3% in the non-endemic regions. Of 1,102 tested ticks, 40 (3.6%) were CCHFV-positive, belonging to H. marginatum (29), Rhipicephalus bursa (10), and Ixodes ricinus (1). The virus strains clustered with clade V and VI related sequences. They fell into two lineages: Kosovo I and II. Kosovo I comprised strains recovered exclusively from R. bursa ticks and was closely related to AP92 prototype strain. Kosovo II clustered into Kosovo IIa, including human-derived strains, and IIb including only strains detected in H. marginatum and I. ricinus. Our phylogeographic reconstruction suggests two temporally distinct CCHFV introductions: the most probable location of the most recent common ancestor of Kosovo I lineage was in Greece (63 years ago) and that of lineages IIa-b in Turkey (35 years ago). After each CCHFV introduction into Kosovo, subsequent lineage expansions suggest periods of in situ evolution. The study provides the first insight into the genetic variability and the origin of CCHFV in ticks from Kosovo. Our findings indicate the spreading of CCHFV to non-endemic areas, which underlines the importance of further studies in order to monitor and predict future CCHF outbreaks in Kosovo. The AP92-like strains appear to be more widespread than previously thought and may provide a promising target for experimental studies due to their assumed low pathogenicity.

Phylogeography of Crimean Congo Hemorrhagic Fever Virus

“…These values were in concordance with previously reported rates of 1.09 x 10 −4 , 1.52 x 10 −4 and 0.58 x 10 −4 ssy in the S, M and L segments [9] and 1.71 x 10 −4 [1.25–2.30 x 10 −4 ] ssy within GtV [7]. Lower substitution rates reported previously in the L segment were suggested to have resulted from a small sample size [9].…”

“…The MRCA of the European GtV (always supported by posterior probability 1) dated back 280 [133–485] years in the S segment, 396 [238–500] years in M and 402 [289–538] years in L segment. This node was dated 1930 [1890–1960] in another study that relied upon partial S segment sequences [7]. Both the use of a full S segment and the inclusion of additionally sequenced viruses could result in a three times older age of this node in our study.…”

“…Much higher substitution rates (2.96 x 10 −4 [1.6–4.7 x 10 −4 ] ssy and 1.7–5.7 x 10 −4 ssy) have been previously reported for partial (ca. 300 or 500 nt) S segment sequences [7, 8]. When we ran the analysis using the same sequences as in the full-segment dataset, but using only the S segment fragment used by Sherifi et al (2014) the substitution rate was 3.4 x 10 −4 [1.76–5.51 x 10 −4 ] instead of 1.3 x 10 −4 [0.62–2.0 x 10 −4 ] for the full S segment.…”

“…This relatively fast dynamics implies that CCHFV in Europe likely did not reach an ecological balance, and that the further spread of CCHFV is very likely. Unfortunately, no complete segment sequences were available for lineage VI (Europe 2), which was apparently introduced to Europe, probably via Turkey, also approximately 100 years ago [7]. It is surprising that the virus, which emerged in Africa several thousand years ago, was introduced and got established in Europe only so recently, given a proven capacity of migratory birds to carry ticks infected with African CCHFV variants [28] and the occasional detection of non-conventional CCHFV genotype variants in Europe [12, 29].…”

“…The most ancient lineages (branching close to the tree root in phylogenetic reconstructions) are generally found in Africa, with the exception of strain Ap92, which was isolated in Greece. Most of the European isolates belong to GtV and are much more conserved than CCHFV circulating elsewhere [3, 7, 8]. Strains related to Ap92 (GtVI) are also occasionally found in Europe [7].…”