Long-term persistence of immunity was assessed in 66 patients who had contracted tick-borne encephalitis (TBE) and in 126 subjects who had completed primary TBE immunization using a conventional three-dose schedule from 3 to 8 years earlier. Immunity was tested in the subjects stratified by age as follows: ≤40 years (N = 37); 41-60 years (N = 100); and over 60 years (N = 55). Antibody levels decreased significantly with increasing age in the vaccinated cohort by comparison with the individuals who had previously contracted TBE. Consistently higher geometric mean antibody levels were found in the patients infected naturally. When the vaccinated subjects were compared, subjects ≤40 years old had significantly higher antibody levels than either of the older groups. Analyzing immunity to TBE over time revealed a remarkable (50%) decline in seroprotection rates in the vaccinated group at 50 months of follow-up, while stable, high levels persisted in all subjects after natural TBE infection. In the vaccinees over 60 years old, the TBE antibody levels reached 60% at 60 months, and 20% at 70 months of follow-up; in contrast, in the 41-60-year-old group, the antibody levels remained high for 70 months, and then fell rapidly. For people aged <60 years old, booster doses are recommended every 5 years after the fourth dose of vaccine, which should be administered 3 years after primary immunization. In subjects aged 60 years or older, booster doses should be given every 3 years.
BackgroundNortheastern Italy is a hotspot for several tick-borne pathogens, transmitted to animals and humans mainly by Ixodes ricinus. Here we compare the results of molecular monitoring of ticks and zoonotic TBPs over a six-year period, with the monitoring of red foxes (Vulpes vulpes) in an endemic area.ResultsIn the period 2011–2016, 2,578 ticks were collected in 38 sites of 20 municipalities of Belluno Province. Individual adults (264), pooled larvae (n = 330) and nymphs (n = 1984) were screened for tick-borne encephalitis virus, Borrelia burgdorferi (s.l.), Rickettsia spp., Babesia spp., Anaplasma phagocytophilum and “Candidatus Neoehrlichia mikurensis” by specific SYBR green real-time PCR assays and sequencing. The spleens of 97 foxes, culled in the period 2015–2017 during sport hunting or population control programs, were also screened. Overall, nine different pathogens were found in I. ricinus nymph and adult ticks: Rickettsia helvetica (3.69%); R. monacensis (0.49%); four species of the B. burgdorferi (s.l.) complex [B. afzelii (1.51%); B. burgdorferi (s.s.) (1.25%); B. garinii (0.18%); and B. valaisiana (0.18%)]; A. phagocytophilum (3.29%); “Candidatus N. mikurensis” (1.73%); and Babesia venatorum (0.04%). Larvae were collected and screened in the first year only and two pools (0.6%) were positive for R. helvetica. Tick-borne encephalitis virus was not found in ticks although human cases do occur in the area. The rate of infection in ticks varied widely according to tick developmental stage, site and year of collection. As expected, adults were the most infected, with 27.6% harboring at least one pathogen compared to 7.3% of nymphs. Pathogens with a minimum infection rate above 1% were recorded every year. None of the pathogens found in ticks were detectable in the foxes, 52 (54%) of which were instead positive for Babesia cf. microti (also referred to as Babesia microti-like, “Theileria annae”, “Babesia annae” and “Babesia vulpes”).ConclusionsThe results show that foxes cannot be used as sentinel animals to monitor tick-borne pathogens in the specific epidemiological context of northeastern Italy. The high prevalence of Babesia cf. microti in foxes and its absence in ticks strongly suggests that I. ricinus is not the vector of this pathogen.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-2726-7) contains supplementary material, which is available to authorized users.
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