Low risk of Lyme borreliosis in a protected area on the Tyrrhenian coast, in central Italy Alessandro Mannelli 1 , Domenico Cerri 2 , Laura Burini 3 , Sabrina Rossi 1 , Sergio Rosati 1 , Tiziana Arata 3 , Marco Innocenti 3 , Maria Clara Grignolo 3 , Gerolamo Bianchi 3 , Albertina Iori 4 & Francesco Tolari 2 1 Dipartimento di Produzioni Animali, Epidemiologia, Ecologia, Universita ` degli Studi di Torino; Italy; 2 Dipartimento di Patologia Animale, Universita ` degli Studi di Pisa, Italy; 3 Istituto Reumatologico E. Bruzzone, Universita ` degli Studi di Genova; Italy; 4 Istituto di Parassitologia, Universita ` di Roma ‘‘La Sapienza’’, Rome, Italy Accepted in revised form 18 January 1999 Abstract. A comprehensive Lyme borreliosis risk assessment process was applied in S. Rossore Es- tate, on the Tyrrhenian coast, near Pisa, Italy. Host-seeking Ixodes ricinus nymphs peaked in May in oak-dominated deciduous wood (median, Q 1 –Q 3 , number of nymphs/50 m dragging = 4.5, 2.5–8), whereas host-seeking larvae peaked in August in the same habitat type (6.0, 4–17/50 m dragging). Preva- lence of I. ricinus infestation was 88.9% in wild ro- dents (n = 11), 64.3% in fallow deer (n = 28) and 0.0% in wild boars (n = 5). Borrelia burgdorferi sensu lato was not isolated from rodents’ organs, and from 80 I. ricinus nymphs and 50 adults. Moreover, PCR for B. burgdorferi sl carried out on 110 nymphs and 12 adult ticks also gave negative results. Forest workers were at higher risk of tick bite than other Estate employees (relative risk (RR): 1.7, p = 0.02). In spite of high levels of tick exposure, B. burgdorferi sl specific antibodies were not detected in sera from Estate personnel (n = 30) and sentinel animals (dogs, n = 23, fallow deer, n = 61). Key words: Epidemiology, Italy, Lyme borreliosis, Risk assessment, Ticks Abbreviations: sl = sensu lato; Q 1 = first quartile of a distribution; Q 3 = third quartile; PCR = polymerase chain reaction; RR = relative risk Introduction The risk of Lyme borreliosis – the most frequent tick- borne zoonosis in the northern hemisphere, caused by the spirochete Borrelia burgdorferi sensu lato (sl) [1] – depends upon the geographical distribution of tick vectors (Ixodes persulcatus complex) [2, 3]. Within the vectors’ geographic range, the intensity of spirochete transmission in natural cycles varies considerably. In 101 habitats, that were examined in 14 European countries within a concerted action project on Lyme borreliosis (EUCALB), prevalence of B. burgdorferi sl infection in host-seeking I. ricinus and I. persulcatus ranged 0–50% and was higher in eastern Europe than in the west. Highest densities of spirochete-infected ticks were found in heterogeneous deciduous forests, and Lyme borreliosis in humans was mostly reported from recreational habitats [4]. Borrelia burgdorferi sl endemic foci have been identified in northern and central Italy [5]. In the northeastern province of Trieste, prevalence of in- fection in I. ricinus nymphs reached 70% [6], whereas spirochetes were sporadically identified in 4000 nymphs and adults collected on the foothills of the Apennines, in the province of Parma [7]. In Italy, Lyme borreliosis risk assessment is particularly im- portant in recreational areas, that are frequented by large number of visitors, and where wooded habitats and abundant wildlife are favorable to ticks [8, 9]. In assessing risk on a small geographical scale, reported cases of Lyme borreliosis are of scarce util- ity, mostly due to diculties in the determination of exposure location and uneven case detection criteria [10]. Conversely, the Ôentomological risk indexÕ (the abundance of infected host-seeking ticks [11]) can be evaluated locally. The prevalence of antibodies against B. burgdorferi sl in exposed human categories and sentinel animals (such as dogs and deer) is an- other sensible indicator that has been used to classify geographic locations with regard to the risk of in- fection [12, 13]. The validity of sero-epidemiological surveys for Lyme borreliosis can be compromised by the diculties encountered interpreting serological tests [14]. In fact, cross reactions with antigens com- mon to dierent microorganisms may lead to false positive results [15]. Recombinant antigens and western blotting can therefore be used to improve test accuracy [16]. European Journal of Epidemiology 15: 371–377, 1999. Ó 1999 Kluwer Academic Publishers. Printed in the Netherlands.