Workgroup Tick-borne Diseases
Institute of Bacterial Infections and Zoonoses
Epidemiology of TBE and other tick-borne diseases
To assess the risk of exposition and to improve prophylaxis and therapy of tick-borne diseases it is necessary to clarify all cases of illness epidemiologically. Especially for TBE it includes also the virus prevalence in tick biotopes to score the risk and the risk areas actually. This is also important for the work of the National Reference Laboratory for tick-borne diseases and our consultation assignments. That’s why we carry out investigations of ticks at several places, for example in the Colbitz-Letzlinger Heide a formerly non risk area in Saxony-Anhalt, in the district Wartburgkreis and Unstrut-Hainich-Kreis in Thuringia, near the town Neustrelitz and on the Island of Rügen in Mecklenburg-West-Pomerania. The reason for our investigations in ticks is very often the first clinical case of human TBE in a formerly non risk area.
Up to now our knowledge about TBE especially in animals are low. That’s why it is of high interest for us to check all clinical TBE cases in animals after natural exposition to infected ticks in TBE risk areas.
In 2006 we diagnosed the first case of tick-borne encephalitis (TBE) in a monkey (Macaca sylvanus) after natural exposition in a TBE risk area including clinical, serological, and neuropathological findings, and distribution of TBE virus (TBEV) in the brain by immunohistochemistry and realtime RT-PCR and nRT-PCR.
The monkey park where the infection occurred is situated in Southern Germany, close to the Bodensee (Bodenseekreis). This is a TBE risk area, flanked in the west by a TBE high risk area (Kreis Konstanz). Between 1999–2005, 25 autochthonous clinical cases of TBE in humans were reported in the Bodenseekreis and 30 in the Kreis Konstanz. The prevalence of TBEV in ticks was between 1.2% and 2.3% in this area.
A female Barbary Macaque (Macaca sylvanus) from a group of ca. 200 animals, kept in a large outdoor enclosure of a monkey park developed staggering, paresis of the hind legs, incoordination and intermittant opisthotonus. Four days after the onset of clinical signs, the animal became comatous and was euthanized. At necropsy, no macroscopic lesions were observed.
Moderate perivascular inflammatory cuffs and slight diffuse infiltration of brain parenchyma by mononuclear cells were observed in almost all brain areas including basal ganglia and cerebellum. In addition, slight mononuclear inflammatory infiltrates were present in the meninges. Immunohistochemically, TBEV antigen was detected in neurons and processes, mainly in the Purkinje cell layer of cerebellar cortex and to a lower extent in pyramidal neurons of the temporal cortex. Although the classical multinodular lesioning pattern of the brain was not observed, the distribution of viral antigens was comparable to that observed in fatal human TBEV infections with short clinical course.
Ten samples of brain tissue were selected for PCR analysis including cerebrum, cerebellum and brain stem. Six out of the10 brain samples were positive and CSF was negative for TBEV by nRT-PCR. The sequencing data of these 6 PCR products show close homology to the sequence of strain Neudoerfl, the prototype strain of the European virus subtype, which suggests that the infection was acquired locally by infected ticks. The serum was tested by ELISA and was positive for TBEV antibodies.
Retrospective analysis of anamnestic data from the affected monkey park shows that TBE may have appeared sporadically in macaques in the past.
In addition, TBEV seroprevalence in free ranging small ruminants was examined. The first results suggested that goats and sheep can be used as TBEV sentinels in defined areas. To verify this further investigations with a large number of animals are recommended.