Tick-borne zoonoses are common even in healthy adults in Northwestern Italy

A study from Northwestern Italy has found unexpectedly high exposure to multiple tick-borne pathogens among healthy adults, including people without symptoms at the time of testing. Across 144 participants, molecular testing detected active or recent pathogen DNA in 19%, while 44% had antibodies against at least one tick-borne agent. The findings underline how much tick-borne circulation may go unnoticed when surveillance focuses only on clinically ill patients.

The study included 144 healthy adults with widely varying exposure to tick bites, from occasional bites to more than 10 per year. Overall, 65% reported at least one tick bite annually. Time spent outdoors and routine body checks after returning from natural environments were both significantly associated with reported bite frequency.

Babesia exposure was particularly frequent

The highest seroprevalence was observed for Babesia divergens, at 22.2%, followed by Babesia microti at 13.9%.

Spotted Fever Group Rickettsia showed 9.3% PCR positivity and 14.3% seroprevalence, while Anaplasma phagocytophilum was detected by PCR in 6.9% of participants and by serology in 12.5%.

For Borrelia burgdorferi sensu lato, responsible for Lyme borreliosis, no participant was PCR-positive, but 3.5% had antibodies, indicating previous exposure. No evidence of tick-borne encephalitis virus infection was detected in the cohort.

High exposure without disease

One of the most striking findings was that all participants were asymptomatic when sampled, despite the relatively high frequency of molecular or serological evidence of exposure. The authors compare this pattern with wildlife populations, where pathogens may circulate extensively without producing obvious disease in every infected host. In humans, this raises questions about how many tick-borne infections remain undiagnosed or clinically silent.

The results do not mean that 44% of the population has active tick-borne disease. Serology primarily indicates previous immune exposure, while PCR positivity provides stronger evidence of pathogen presence at the time of sampling. The study also involved a relatively small, exposure-enriched cohort and therefore should not be extrapolated directly to the entire Italian population.

A sentinel population for emerging zoonoses

People who spend substantial time outdoors can nevertheless provide an important warning system for changing tick ecology. The authors argue that stratifying populations by tick exposure could improve epidemiological surveillance and help physicians recognise infections that may otherwise be overlooked. As climate, land use and wildlife distribution alter the geographic range and activity periods of ticks in Europe, this type of surveillance could become increasingly important.

The conclusion is therefore less about overt disease than silent circulation: several zoonotic pathogens were detectable in apparently healthy people repeatedly exposed to ticks, suggesting that routine clinical case counts may capture only part of the real transmission landscape.