Goats as sentinel hosts for the detection of tick-borne encephalitis risk areas in the Canton of Valais, Switzerland.

BACKGROUND: Tick-borne encephalitis (TBE) is an important tick-borne disease in Europe. Detection of the TBE virus (TBEV) in local populations of Ixodes ricinus ticks is the most reliable proof that a given area is at risk for TBE, but this approach is time-consuming and expensive. A cheaper and simpler approach is to use immunology-based methods to screen vertebrate hosts for TBEV-specific antibodies and subsequently test the tick populations at locations with seropositive animals. RESULTS: The purpose of the present study was to use goats as sentinel animals to identify new risk areas for TBE in the canton of Valais in Switzerland. A total of 4114 individual goat sera were screened for TBEV-specific antibodies using immunological methods. According to our ELISA assay, 175 goat sera reacted strongly with TBEV antigen, resulting in a seroprevalence rate of 4.3%. The serum neutralization test confirmed that 70 of the 173 ELISA-positive sera had neutralizing antibodies against TBEV. Most of the 26 seropositive goat flocks were detected in the known risk areas in the canton of Valais, with some spread into the connecting valley of Saas and to the east of the town of Brig. One seropositive site was 60 km to the west of the known TBEV-endemic area. At two of the three locations where goats were seropositive, the local tick populations also tested positive for TBEV. CONCLUSION: The combined approach of screening vertebrate hosts for TBEV-specific antibodies followed by testing the local tick population for TBEV allowed us to detect two new TBEV foci in the canton of Valais. The present study showed that goats are useful sentinel animals for the detection of new TBEV risk areas.

Presence of Chlamydiales DNA in ticks and fleas suggests that ticks are carriers of Chlamydiae.

The Chlamydiales order includes the Chlamydiaceae, Parachlamydiaceae, Waddliaceae, Simkaniaceae, Criblamydiaceae, Rhabdochlamydiaceae, Clavichlamydiaceae, and Piscichlamydiaceae families. Members of the Chlamydiales order are obligate intracellular bacteria that replicate within eukaryotic cells of different origins including humans, animals, and amoebae. Many of these bacteria are pathogens or emerging pathogens of both humans and animals, but their true diversity is largely underestimated, and their ecology remains to be investigated. Considering their potential threat on human health, it is important to expand our knowledge on the diversity of Chlamydiae, but also to define the host range colonized by these bacteria. Thus, using a new pan-Chlamydiales PCR, we analyzed the prevalence of Chlamydiales DNA in ticks and fleas, which are important vectors of several viral and bacterial infectious diseases. To conduct this study, 1340 Ixodes ricinus ticks prepared in 192 pools were collected in Switzerland and 55 other ticks belonging to different tick species and 97 fleas belonging to different flea species were harvested in Algeria. In Switzerland, the prevalence of Chlamydiales DNA in the 192 pools was equal to 28.1% (54/192) which represents an estimated prevalence in the 1340 individual ticks of between 4.0% and 28.4%. The pan-Chlamydiales qPCR was positive for 45% (25/55) of tick samples collected in Algeria. The sequencing of the positive qPCR amplicons revealed a high diversity of Chlamydiales species. Most of them belonged to the Rhabdochlamydiaceae and Parachlamydiaceae families. Thus, ticks may carry Chlamydiales and should thus be considered as possible vectors for Chlamydiales propagation to both humans and animals.

Prevalence and phylogenetic analysis of tick-borne encephalitis virus (TBEV) in field-collected ticks (Ixodes ricinus) in southern Switzerland.

BACKGROUND: Tick-borne encephalitis is the most common tick-borne viral infection in Europe with 3,000 human cases reported each year. In Western Europe, the castor bean tick, Ixodes ricinus, is the principal vector of the tick-borne encephalitis virus (TBEV). TBEV appears to be spreading geographically and was recently detected for the first time in Canton Valais in the southern part of Switzerland. The purpose of the present study was to survey the I. ricinus tick populations of Canton Valais for TBEV. METHODS: We collected a total of 19,331 I. ricinus ticks at 45 different sites in Canton Valais between 2010 and 2013. Ticks were processed in pools and tested for TBEV using reverse transcription quantitative PCR. The NS5 gene and the envelope gene of the TBEV isolates were partially sequenced for phylogenetic analysis. RESULTS: TBEV was detected in tick populations at six of the 45 sites. These six sites were all located in a 33 km transect along the Rhône River. TBEV was detected in two sites for three of the four years of the study showing the temporal persistence of the pathogen. Prevalence of TBEV in the six positive sites ranged from 0.16% to 11.11%. Phylogenetic analysis found that all TBEV isolates from Canton Valais belonged to the European subtype. Genetic analysis found two distinct lineages of TBEV suggesting that Canton Valais experienced two independent colonization events. CONCLUSIONS: TBEV appears to be well established at certain locations in Canton Valais.