Tick-borne diseases: an emerging public health problem?

Among the vector-borne pathogens, those transmitted by ticks, principally Rhipicephalus sanguineus and Ixodes ricinus, are most widespread in Europe with increasing concern for human health. Over the past two decades the incidence of Lyme Diseases and TBE has increased, commonly by an order of magnitude. Cases of human granulocytic ehrlichiosis (HGE), rickettsiosis (R. helvetica) and babesiosis, although still rare, are also increasing. A clear explanation of this emergence is still not available but the spread of tick population within new habitat created as consequences of the global changes (climate and land use changes), the increase in tick habitat use by humans for a series of purposes (recreational and occupational) and the amelioration of the diagnostic tools are considered as the main reasons. Because of the yearly variation in tick abundance determined by variation in climatic condition and host densities, there are still lack of quantitative data useful to assess if an increase in average of I. ricinus abundance in Italy has occurred during the last decades, but increasing evidences indicate an altitudinal shift of tick occurrence toward higher altitudes and new habitat. Among the other tick species which act as vector for pathogen in humans in Italy, the tick R. sanguinius represent an increasing public health problem in Mediterranean area. New rickettsial infections (spotted fever group rickettsial strain Bar29) and zoonotic Babesia have been recently reported in human beings both from Italy and other European countries where the tick is endemic in dogs and other hosts (Cardenosa et al., 2003, European J Epidemiol 18: 351-356; Herwarldt et al., 2003, Emerging Inf Dis 9: 942-948). Rickettsia slovaca has also been recently found in Dermacentor marginatus collected in Sicily. This rickettsia species has shown to be responsible for a disease known as "tick-borne lymphadenopathy" that could potentially be misinterpreted as Mediterranean Spotted Fever (Cazorla et al., 2003, Emerg Infect Dis, 9: 135). These findings underscore the importance of using antigens from other SFG Rickettsiae in addiction to that of R. conorii in serodiagnosis of MSF in Italy. These could include for example R. helvetica, R. slovaca, and R. mongolotimonae, which are present in Ixodid ticks from European countries. The expanding geographic spread of R. conorii is also of concern. New human cases of infection are now currently diagnosed also in northern regions of Italy, such as Lombardy and Piedmont, associated with positive serology in dogs (Mannelli et al., 2003, Preventive Vet Med 60: 13-26; Melgrati etal., 1999, Giornale It Mal Inf 5: 34-39). By other end, the human tick bites seems to be increasing. Out of more than 1500 tickbites reported from human population in Liguria and Trentino, most of identified cases were from I. ricinus, but a high frequency of R. sanguineus bites was also observed (about 35%).