Dermacentor reticulatus is a vector of tick-borne encephalitis virus.

Tick-borne encephalitis virus (TBEV; family Flaviviridae) is the most medically important tick-borne virus in Europe and Asia. Ixodes ricinus and I. persulcatus ticks are considered to be the main vector ticks of TBEV in nature due to their specific ecological associations with the vertebrate hosts. Nevertheless, recent TBEV prevalence studies in ticks suggest that Dermacentor reticulatus ticks might play a relevant role in the maintenance of TBEV in nature. The goal of this study was to evaluate the vector competency of D. reticulatus for TBEV through experimental tick infections and comparative in vivo transmission studies involving D. reticulatus and I. ricinus ticks. We observed that after a transcoxal micro-capillary inoculation, adult female D. reticulatus ticks efficiently replicated TBEV during the observed period of 21 days. The mean virus load reached up to 2.5 × 105 gene copies and 6.4 × 104 plaque forming units per tick. The infected D. reticulatus ticks were able to transmit the virus to mice. The course of infection in mice was comparable to the infection after a tick bite by I. ricinus while the virus spread and clearance was slightly faster. Moreover, D. reticulatus ticks were capable of tick-to-tick non-viraemic transmission of TBEV to the Haemaphysalis inermis nymphs during co-feeding on the same animal. The co-feeding transmission efficiency was overall slightly lower (up to 54 %) in comparison with I. ricinus (up to 94 %) and peaked 1 day later, at day 3. In conclusion, our study demonstrated that D. reticulatus is a biologically effective vector of TBEV. In line with the recent reports of its high TBEV prevalence in nature, our data indicate that in some endemic foci, D. reticulatus might be an underrecognized TBEV vector which contributes to the expansion of the TBEV endemic areas.

Ličková M ，Fumačová Havlíková S ，Sláviková M ，Slovák M ，Drexler JF ，Klempa B ... -  《-》

Ixodid ticks and tick-borne encephalitis virus prevalence in the South Asian part of Russia (Republic of Tuva).

The most significant processes of arbovirus evolution can be expected to occur in the territories where ticks of different species cohabitate and at the boundaries of virus occurrence, where the probability of the appearance of new virus variants is high due to the possible shift in the main vectors and/or vertebrate hosts. One of the most interesting regions in this regard is the Republic of Tuva. Since most of its territory is covered by mountain ranges and intermountain basins, we were able to study the distribution of vectors and viruses in geographically isolated areas at different altitudes and in various landscapes. From 2008 to 2017, we conducted six expeditions to Tuva and collected 3,077 adult ticks and 24 nymphs. The distribution of tick species was confined to specific landscapes, as follows: Dermacentor nuttalli occurred in steppes, D. silvarum inhabited forest-steppe areas, and Ixodes persulcatus inhabited mixed forests. All three species of ticks were collected on plains and mountain slopes. The range of D. silvarum was shown to be lower than 1300 m above sea level (a.s.l.). Only D. nuttalli and I. persulcatus were collected at higher altitudes. According to our observations, single nymphs of D. nuttalli appear on animals one month before larvae appear. This finding confirms the hypothesis that the immature forms of D. nuttalli are able to overwinter under favourable conditions. We isolated 9 strains and 3 isolates of tick-borne encephalitis virus (TBEV) from I. persulcatus, one strain from D. nuttalli and one strain from D. silvarum. The TBEV strain from D. nuttalli was isolated from the territory inhabited only by Dermacentor ticks. All isolated strains belong to the Siberian subtype of TBEV. TBEV was detected in ticks from all the investigated altitudes. There were no statistically significant differences in the virus prevalence between the Dermacentor and Ixodes ticks. The results of our work provide additional support for the hypothesis of the existence of TBEV foci in areas with an absolute dominance of D. nuttalli.

Kholodilov I ，Belova O ，Burenkova L ，Korotkov Y ，Romanova L ，Morozova L ，Kudriavtsev V ，Gmyl L ，Belyaletdinova I ，Chumakov A ，Chumakova N ，Dargyn O ，Galatsevich N ，Gmyl A ，Mikhailov M ，Oorzhak N ，Polienko A ，Saryglar A ，Volok V ，Yakovlev A ，Karganova G ... -  《-》

Prevalence of tick-borne encephalitis virus in questing Dermacentor reticulatus and Ixodes ricinus ticks in Lithuania.

The Baltic States are the region in Europe where tick-borne encephalitis (TBE) is most endemic, with one-third of the European TBE cases detected in Lithuania, Latvia and Estonia. With the Czech Republic and Germany, Lithuania has among the highest population incidences of TBE. Ticks from the Ixodidae family are the main vectors of the TBE virus (TBEV) in Europe. However, there is still a lack of data on the prevalence of TBEV in ticks in different parts of Lithuania. This study analysed the current prevalence of TBEV in the two most common tick species distributed in Lithuania: Ixodes ricinus and Dermacentor reticulatus. Questing I. ricinus (n = 7170) and D. reticulatus (n = 1676) ticks were collected from 81 locations in all ten counties of Lithuania between 2017 and 2019. The presence of TBEV was analysed using a real-time reverse transcription polymerase chain reaction (RT-PCR) and TBEV prevalence in ticks was calculated as the minimum infection rate (MIR). TBEV was detected in the three developmental stages (adults, nymphs and larvae) of I. ricinus and in D. reticulatus adults. The MIR of TBEV in the total sample of I. ricinus was 0.4 % (28/7170) and for D. reticulatus was also estimated to be 0.4 % (6/1676). TBEV-infected ticks were found in 16 locations in seven counties, with MIR ranging from 0.1 % to 1.0 %. The TBEV strains detected belong to the European subtype. To the best of the authors' knowledge, this is the first report on the prevalence of TBEV in unfed D. reticulatus ticks and in I. ricinus unfed larvae in Lithuania.

Sidorenko M ，Radzijevskaja J ，Mickevičius S ，Bratčikovienė N ，Paulauskas A ... -  《-》

Repeated isolation of tick-borne encephalitis virus from adult Dermacentor reticulatus ticks in an endemic area in Germany.

Chitimia-Dobler L ，Lemhöfer G ，Król N ，Bestehorn M ，Dobler G ，Pfeffer M ... -  《Parasites & Vectors》

Prevalence of tick-borne encephalitis virus in Ixodes ricinus and Dermacentor reticulatus ticks collected from the Lublin region (eastern Poland).

A total of 875 nymphal and adult Ixodes ricinus ticks and 148 adult Dermacentor reticulatus ticks were collected by flagging lower vegetation in the Lublin region (eastern Poland) and examined for the presence of RNA of tick-borne encephalitis virus (TBEV) by nested RT-PCR. The minimum infection rate of I. ricinus ticks with TBEV amounted to 1.6% while the infection rate of D. reticulatus ticks was 10.8%. The results suggest that D. reticulatus may be a potential vector of TBEV in Central Europe.

Wójcik-Fatla A ，Cisak E ，Zając V ，Zwoliński J ，Dutkiewicz J ... -  《-》