The focal distribution of tick-borne encephalitis virus (TBEV; Flaviviridae, Flavivirus) appears to depend mainly on cofeeding transmission between infected Ixodes ricinus L. nymphs and uninfected larvae. To better understand the role of cofeeding ticks in the transmission of TBEV, we investigated tick infestation of rodents and the inßuence of microclimate on the seasonality of questing I. ricinus ticks. A 3-yr study was carried out at four sites, including two conÞrmed TBEV foci. Free-living ticks and rodents were collected monthly, and microclimatic data were recorded. A decrease in questing nymph density was observed in 2007, associated with low relative humidity and high temperatures in spring. One site, Thun, did not show this decrease, probably because of microclimatic conditions in spring that favored the questing nymph population. During the same year, the proportion of rodents carrying cofeeding ticks was lower at sites where the questing nymph density decreased, although the proportion of infested hosts was similar among years. TBEV was detected in 0.1% of questing ticks, and in 8.6 and 50.0% of larval ticks feeding on two rodents. TBEV was detected at all but one site, where the proportion of hosts with cofeeding ticks was the lowest. The proportion of hosts with cofeeding ticks seemed to be one of the factors that distinguished a TBEV focus from a non-TBEV focus. The enzootic cycle of TBEV might be disrupted when dry and hot springs occur during consecutive years.
This study is part of a project that aimed to better understand the role of small mammals in the maintenance of the tick-borne encephalitis virus at four different sites in Switzerland. Here we focused on the detection of three intracellular pathogens, Anaplasma phagocytophilum, Rickettsia spp., and Babesia spp., in field-derived ticks that detached from 79 small mammals. We analyzed 465 Ixodes ricinus larvae after their molt and 14 semiengorged I. trianguliceps that were feeding on rodents. No pathogen was detected in I. trianguliceps. In I. ricinus, the most frequently detected pathogen was Rickettsia spp. (7.3%). All Rickettsia spp. identified DNA belonged to R. helvetica except one DNA sample that was identified as R. monacensis. The prevalence of Babesia spp. reached 2.4% and identification at the species level revealed B. venatorum (1.7%) and B. microti (0.4%). A. phagocytophilum was not detected in I. ricinus that detached from rodents. To verify the absence of A. phagocytophilum at the four sites, additional questing nymphs collected at these sites were analyzed for A. phagocytophilum. This pathogen was detected at one site only, where 2% (2/100) of questing ticks were infected. Some of these emerging pathogens are described for the first time in molted larvae that fed on rodents. The presence of medically relevant pathogens, with a global prevalence of 9.9%, highlights the importance to inform the medical corporation on the risk for human health in these areas.
Tick-borne encephalitis virus (TBEV) is the causative agent of tick-borne encephalitis (TBE) and causes neurological disease in humans in Eurasia. TBEV is transmitted by ticks of the genus Ixodes. Currently 10,000 Ð12,000 clinical cases are reported annually in Ϸ30 TBE endemic countries. Since 1990 the epidemiology of TBE is characterized by a global increase of clinical cases and an expansion of risk areas. Similar trends are also observed in Switzerland but few studies conÞrmed the emergence of new TBE foci by detecting viral RNA in Þeld-collected ticks. In this study, free-living Ixodes ricinus (L.) ticks from one nonendemic and three new TBE endemic regions located in the Western part of Switzerland were screened during four consecutive years (2007Ð2010) for the presence of TBEV. A total of 9,868 I. ricinus ticks (6,665 nymphs and 3,203 adults) were examined in pools for TBEV by real-time reverse transcription polymerase chain reaction. Our results conÞrmed the presence of viral RNA in 0.1% (6/6120) of questing ticks collected in one new endemic region. Among TBE endemic sites, the minimal infection rate per 100 ticks tested ranged from 0.21 (1/477) to 0.95 (1/105). Four positive samples were sequenced and phylogenetic analysis of the NS5 gene showed that all TBEV nucleotide sequences belonged to the European subtype and were split into two distinct lineages originating probably independently from two distinct foci located NorthÐEast and East of the study region.
In a previous study, the presence of tick-borne encephalitis virus (TBEV) in questing Ixodes ricinus L. ticks and in Þeld derived ticks that engorged on small mammals (n ϭ 9,986) was investigated at four sites located in a TBE area in Switzerland. Two of these sites were already recognized as TBE foci (Thun and Belp) and the screening of ticks revealed the presence of TBEV in ticks at a third site, Kiesen, but not at the fourth one, Trimstein. The aim here was to test another approach to detect TBE endemic areas. Sera from 333 small mammals (Apodemus flavicollis, A. sylvaticus, Myodes glareolus) captured in 2006 and 2007 at the four sites were examined for the presence of antibodies against TBEV using immunoßuorescence and avidity tests. Overall the prevalence of antibodies against TBEV in rodents reached 3.6% (12/333). At two sites known as TBE foci, Thun and Belp, anti-TBEV antibodies were detected in 9.9% (9/91) and 1.6% (1/63) of rodent sera, respectively. At the third site, Kiesen, recently identiÞed as a TBE focus by the detection of TBEV in ticks, anti-TBEV antibodies were detected in 1.8% (2/113) of rodent sera. Finally, at Trimstein, none of the examined rodent sera had antibodies against TBEV (0/66). This study shows another approach to detect TBE foci by testing antibodies in small mammal sera that is less time-consuming and less expensive than molecular tools.
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