Ticks are amongst the most important vectors of diseases in temperate climates (Heyman et al. 2010) and display a worldwide distribution being adapted to different environments, climate and host species (Danta-Torres et al. 2012). Their medical and veterinary relevance is mostly due to their great capacity of transmitting viral, bacterial, protozoan and helminthic infections, which may cause a diverse range of affections, commonly referred to as tick-borne diseases (TBDs) (Sonenshine et al. 2018). Many TBDs are zoonosis, such as Rickettsiosis, Lyme Borreliosis, Anaplasmosis (Alciati et al. 2001) and TBE (tick-borne encephalitis). These diseases can evolve as asymptomatic or manifest themselves symptomatically with the involvement of the central nervous system, leading to death the patient, but also of skin system, vascular system. People more at risk are children, elderly and immunosuppressed subjects.
Rickettsiosis is a bacterial disease; it is caused by an obligate intracellular α-proteobacteria, gram negative, pleomorphic bacillus of the genus Rickettsia. In Italy, the regions most affected are Sicily, Sardinia, Lazio and Calabria. Until 2002, Rickettsia conorii conorii was the only pathogenic Rickettsia recorded in Italy as causal agent of Mediterranean Botton Fever (FBM). Today, molecular techniques have allowed the identification of other Rickettsia species. Actually, a growing number of new Rickettsiae were described and recognized as causative agents of human diseases diagnosed in Europe during the last decades. Twenty-six Rickettsia species with validated and published names are currently reported (Parola et al. 2013).
Borrelia burgdorferi is the etiological agent of Lyme borreliosis. Lyme disease typically presents with an erythema migrans rash and non-specific symptoms such as fatigue, fever, headache and muscle and joint pains and, if left untreated, it can become a multisystem disease. Lyme disease is rarely fatal, but deaths linked to Lyme carditis have recently been reported (Seltzer et al. 2000, Kugeler et al. 2011). In Italy, the most affected regions are Friuli-Venezia Giulia, Liguria, Veneto, Emilia-Romagna, Trentino Alto Adige (Autonomous Province of Trento), while B. burgdorferi is reported sporadically in the southern central regions and islands (website Epicentro, ISS).
Anaplasma phagocytophilum is responsible for granulocytic anaplasmosis. Clinically, people can have asymptomatic A. phagocytophilum infections, but most frequently have non-specific symptoms (e.g. fever, headache and muscle aches). The fatality rate is less than 1% (Dumler et al. 2005, Biggs et al. 2016).
These zoonotic TBDs may be associated with both domestic and wild animals, with a high risk of acquiring infections for humans frequenting tick-infested areas, such as forests, meadow habitats and grasslands (Danta-Torres et al. 2012, Jaensen et al. 2009, Medlock et al. 2013). TBDs are constantly expanding worldwide and their incidence has increased over the past few years (Danta-Torres et al. 2012). This increase is closely related to survival and spread of vectors that depend on different climatic and environmental factors. Local climatic factors (macro- and micro-climate) can facilitate the appearance or reappearance of vector-borne diseases in a given area. (Jongejan et al. 2004). Seasonality, distribution, and prevalence of TBDs are influenced significantly by climate factors, primarily high and low temperature extremes and precipitation patterns. Climate changes can result in modified weather patterns and an increase in extreme events that can affect disease outbreaks by altering biological variables such as vector population size and density, vector survival rates, the relative abundance of disease-carrying animal, reservoir hosts, and pathogen reproduction rates. (Gage, K. L et al. 2008). Collectively, these changes may contribute to an increase in the risk of pathogens being carried to humans. Mediterranean regions are areas with considerable geographical and wildlife diversity, with high environmental variability due to the influence of altitude and distance from the sea. The variability of environmental characteristics favours the formation of tick populations. With about 40 species (Manilla et al. 1998), tick fauna in Italy is one of the most diverse across Europe, with more species than countries such as Portugal (Santos-Silva et al. 2011) and UK (Scharlemann et al. 2008, Smith et al. 2011). Italy, in particular, extends its territory for about 10 parallels presenting a high wealth of different habitats; moreover, given its geographical location, it represents an important bridge in the Mediterranean for the passage of new pathogens from the African to the European continent.
The incidence of human TBDs in Italy is likely underestimated because of poor surveillance and the limited number of available studies. Since 2011, the Istituto Zooprofilattico Sperimentale of Piedmont, Liguria and Valle d’Aosta (IZS PLVA), a public health institute which operates in North-Western Italian regions, is actively involved in TBD surveillance on the territory. The Institute offers an important service to support the general practitioners in the clinical diagnosis of TBDs, by analysing ticks collected from humans. Ticks are identified on morphological basis at the species level and subjected to biomolecular investigations (PCR) for the detection of Rickettsia spp., Borrelia spp., and Anaplasma phagocytophilum. Aim of this study is to report the results of the surveillance carried out during years 2017–2019 in North-Western Italy.