[Tick borne zoonosis: selected clinical and diagnostic aspects]

Tick-borne zoonotic infections are among the most diffuse vector borne diseases: these large group of infections is caused by different microorganisms: Babesia spp., Borrelia spp., Rickettsia spp., Ehrlichia spp., Francisella tularensis, Coxiella burnetii) and tick-borne encephalitis virus. Babesiosis is caused by the protozoa (sporozoa) Babesia microti and it is quite rare in humans in Europe. The ixodids ticks are the competent vectors. A few symptomatic cases have been reported, mainly in splenectomized patients. The laboratory diagnosis is made by the microscopic identification of the parasites within the red blood cells in blood smears. The serologic diagnosis, based mainly upon IFA and WB techniques has only an epidemiological interest. Lyme borreliosis (Lyme disease) has been recognized as the most frequent vector borne disease in mild climate areas. The etiologic agent is a spirochete, belonging to the Borrelia burgdorferi sensu lato complex: B. burgdorferi sensu stricto, B. garinii and B. afzelii. Several additional species of this geno-complex have been identified but their pathogenic capability for humans still needs to be elucidated. Lyme borreliosis is clinically divided into three different clinical stages: the early disease, the disseminated infection and the persistent infection. Individual stages are caused by the diffusion of the spirochetes to different anatomic districts of the body. The main clinical symptoms are, for each stage: the erythema chronicum migrans in the early infection, the peripheral nerves and joint involvement in disseminated diseases and the acrodermatitis chronica atrophica (ACA) with central nervous system involvement in the late disseminated infection. The microbiological diagnosis is achieved by serologic techniques (IFA, EIA, WB) and by isolation of the spirochetes (in vitro culture and DNA amplification methods). Tick-borne relapsing fever (TBRF) is occasionally transmitted to humans by the soft ticks Ornithodorus and is caused by Borrelia spp. Different borreliae are responsible for TBRF in various geographic areas. The laboratory diagnosis is based upon the identification of spirochetes in peripheral blood by microscopic observation of Giemsa stained smears. Rickettsiosis diseases are caused worldwide by the obligate intracellular bacteria belonging to the genus Rickettsia. In the Mediterranean area the most frequently identified rickettsia is R. conorii, that causes the so called Mediterranean spotted fever. The serologic detection of a specific antibody response by IFA techniques is the most prominent tool for the diagnosis. In addition, the PCR method can be applied. Bacteria of the genus Ehrlichia are well known pathogens in veterinary medicine. Since the last decade their zoonotic capability has emerged and E. chafeensis, E. canis and the so called human granulocytic agent (HGE) have been identified in human diseases following a tick bite. The ehrlichiosis is characterized, in human, by a mild fever associated with lymphoadenopathy. The diagnosis is made on the identification of morulae (the intracytoplasmatic inclusion of the growing rickettsiae) in the white cells of peripheral blood. In addition the molecular diagnosis is also possible by PCR. Tick-borne encephalitis (TBE) is the only viral arthropod-borne encephalitis in Europe: it is caused by a flavivirus and it can also be transmitted by the ingestion of goat raw milk. The more relevant epidemiological figure is limited to the Alps, in particular to the Northern side (Austria). Isolated cases have been reported also in Italy. TBE is a benign self-limiting illness that usually recovers without any reliquate. The laboratory diagnosis is obtained by isolating the virus in cell cultures from the CSF or blood of acute phase patients. Serology is anyway the main laboratory tool to perform this diagnosis. Complement fixation and EIA IgM are the most used methods: the latter technique is particularly sensitive in early infection.