RESUMEN
In Switzerland, tick-borne encephalitis (TBE) is a notifiable human disease with an average of 210 cases per year in the last 10 years (2008-2017). A national surveillance conducted in 2009 reported a prevalence of 0.46% for tick-borne encephalitis virus (TBEV) detected in ticks, which is in accordance with the prevalences found in Europe from 0.1%-5%. The Canton of Ticino in the southern part of Switzerland, geographically separated from the rest of the national territory by the Alps, is considered a non-endemic region, as no autochthonous clinical cases and no TBEV presence in ticks have ever been reported. In order to understand the epidemiological situation in Ticino, we conducted a large study investigating the TBEV presence in field-collected Ixodes ricinus ticks and in goat and human sera. Goats and sheep were considered as sentinel hosts showing persistence of antibodies also after 28 months in the absence of symptoms; this longevity supports the data validity to characterize an area with the TBEV status. The goat sera collection was composed of a total of 662 samples from 37 flocks. The total seroprevalence was 14.6%. 39 (40%) of the 97 SNT-positive samples showed an antibody titer ≥ 1:120 which indicates recent infection and consequently the probable presence of active foci among the pastures frequented by the goats belonging to 10 flocks. In total, 51 owners participated in the study and all were TBEV antibody-free. A total of 12'052 I. ricinus ticks (nymphs and adults) were collected and 1'371 pools were tested using quantitative real-time RT-PCR. Only one positive pool was reported with a prevalence of 0.35%. Metagenomic analysis revealed that the TBEV strain isolated from the ticks collected in Ticino is closely related to 2 strains coming from the Canton of Valais (99.1% and 98.7% identity, respectively), a neighbouring region of the Canton of Ticino. These two Cantons are close together but separated by high mountains (Alps) and we hypothesize that infected ticks were transported by wild animals from Valais into the Valle Maggia in Ticino where we found positive ticks. In conclusion, our data show for the first time the presence of TBEV in ticks and the related sero-reactivity in goats, confirming the presence of TBEV in the environment of the Canton of Ticino. Further surveillance studies will have to be conducted to follow the persistence of TBEV in this region.
Asunto(s)
Anticuerpos Antivirales/sangre , Virus de la Encefalitis Transmitidos por Garrapatas/aislamiento & purificación , Encefalitis Transmitida por Garrapatas/veterinaria , Cabras/virología , Ixodes/virología , Infestaciones por Garrapatas/veterinaria , Animales , Virus de la Encefalitis Transmitidos por Garrapatas/genética , Encefalitis Transmitida por Garrapatas/epidemiología , Cabras/parasitología , Humanos , Metagenómica , Ninfa/virología , Prevalencia , ARN Viral/sangre , ARN Viral/aislamiento & purificación , Reacción en Cadena en Tiempo Real de la Polimerasa , Estaciones del Año , Análisis de Secuencia de ADN , Estudios Seroepidemiológicos , Suiza/epidemiología , Infestaciones por Garrapatas/epidemiologíaRESUMEN
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.