Dermacentor reticulatus und Babesia canis

Episode von Tierärztliche Fakultät - Digitale Hochschulschriften der LMU - Teil 07/07 von Ludwig-Maximilians-Universität München · 12. Juli 2014

During the last years, a spreading of the endemic hard tick species Dermacentor reticu-latus and the transmitted canine babesiosis (respectively through the causative agent Babesia canis) was reported for Germany. To answer the question of the probability of further spreading, more detailed information on the epidemiological situation, the eco-logical niche of the tick and studies on the local prevalence of B. canis in D. reticulatus are required. During the last years, the use of geographical information systems (GIS) became common to process questions of species ecology.

In the presented study, Bavarian habitats of D. reticulatus were searched for and charac-terized by analog and digital data sources, in order to gain further information on the tick’s epidemiological situation and also on its ecological niche. The possibility to create a reasonable digital risk map was evaluated. This map was meant to describe a potential distribution of D. reticulatus in Bavaria, by using the results of the digital spatial analysis. Collected D. reticulatus were screened for B. canis by molecular biological methods.

The tick collection was carried out at 61 sampling sites during the biphasic activity pe-riod of D. reticulatus in the sampling years 2010 to 2013. Ticks were collected by the flagging method. Additionally, Bavarian veterinarians, pet owners and hunters were asked to report findings of D. reticulatus or to send in collected ticks. At all sampling sites climate data and information on ecosystem and vegetation were recorded. Digital spatial analysis and creation of the digital risk map were conducted with ArcMap GIS-tool. A conventional PCR targeting the 18S rRNA gene was carried out to detect B. ca-nis. Positive PCR-products were sequenced.

A total of 4085 ticks were collected: 3746 (91.7%) I. ricinus (2095 adult, 482 larva, und 1169 nymphs) and 339 (8.3%) D. reticulatus (all adult; 214 female, 125 male). Another five adult D. reticulatus (collected from dogs) were sent in. Three habitats were positively evaluated for D. reticulatus: two forest areas (in the east of Regensburg and in the north-east of Munich) and the Isar floodplains between Munich and Freising. The site at the Isar floodplains is the first evidence of an endemic habitat in Bavaria in which D. reticulatus could be collected from the vegetation during several activity periods.

The ecosystems of the positively evaluated sites differ, but they are all characterized by the presence of mixed forests – consisting of typical plant type associations – and a large amount of small surface waters. The endemic site is a river-related mixed forest, a floodplain site, showing signs of anthropogenic influence. The soil of the positively evaluated sites shows areas with extreme humid character. In the endemic area, soil consists mainly of clay and gley with a high water retention capacity. Availability of potential game animal hosts is high in all habitats. A population of red deer, which oc-curs seldom in Bavaria, inhabits the endemic D. reticulatus habitat. The digital spatial analysis revealed mean yearly temperatures of 8.5°C for the endemic habitat. This value is lower than the formerly presumed minimum yearly mean temperature of 9.0°C for D. reticulatus in Germany. A digital risk map could be created by using the results of the digital spatial analysis. The created risk map shows 15 forest sites all over Bavaria, which provide a similar combination of environmental variables than the endemic site. Six of these forest areas were evaluated during the field survey, revealing D. reticulatus in two areas. Therefore a positive prognostic value should be assumed for the created risk map. The overall presence of B. canis in the collected D. reticulatus was 0.3%. B. canis was only detected in ticks from the endemic site in Munich.

This study showed that D. reticulatus is endemic in Bavaria. The climatic tolerance of D. reticulatus is wider than formerly assumed. A further spreading of the tick in Bavaria is likely due to the fact that further suitable habitats in Bavaria occur. Red deer should be considered as main transportation vector. The results of the risk map give a reasonable indication in which areas further field survey should be carried out with priority. A further digital based processing of the distribution of D. reticulatus is likely to produce valuable results. The prevalence of B. canis in the area of Munich is low compared to the results of previous studies. Moreover an increase of the prevalence during the next years should be considered. Veterinarians’ attention should be drawn to the risk of au-tochthonous canine babesiosis infections.

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