Borrelia burgdorferi s.l. among questing ticks and small mammals in northern Spain natural reserve (Sierra del Sueve-Asturias)

Abstract

1. Introduction Lyme borreliosis is an arthropod-borne disease distributed worldwide. The first reported cases of human Lyme disease in Spain were published in 1977 (Uruñuela-Bernedo and Diaz Sosa, 1977) and 1987 (Uria et al., 1987), both in northern half of the country, the first one in the Basque Country and the last one in Asturias. Small mammals have been described as important reservoir host for Borrelia burgdorferi sensu lato in different European studies. However, low prevalence of infection (0.5%) was found in a Basque Country study (Gil et al., 2005). This study was conducted to assess the presence of Borrelia burgdorferi s.l., the causative agent of Lyme Borreliosis, in questing ticks and small mammals in Asturias. The study is part of a research project which also deals with the population dynamics of ixodid ticks. 2. Methods and Results Questing ticks were collected from six different areas that covered most of the ecological biotopes in the natural reserve “Sierra del Sueve” located in the province of Asturias. Ticks were collected from vegetation by blanket dragging (1 x 1m). Sampling at each site was conducted twice a month from April 2010 to December 2013. Small mammals were captured, between October 2012 and October 2013, in the same areas previously described for the ticks’ blanket dragging. Sherman traps were placed overnight and trapped animals, were brought to the laboratory for classification (19 Apodemus sylvaticus, 2 Microtus lusitanicus, 1 A. flavicolis, , 1 M. agrestis, 1 Microtus sp., 1 Crocidura russula and 1 C. suaveolens), tick count (ranging 0-8 I.ricinus larvae) and tissue collection (ear, lung, heart, liver, spleen, kidney and urinary bladder) for PCR. 920 nymphs (184 pools) and 60 adults (individual samples) ticks, as well as 26 small mammals’ tissue pools, were examined by polymerase chain reaction (PCR) for the presence of Borrelia burgdorferi s.l. (Clark et al. in 2005). In positive PCR samples, the rrs-rrlA intergénico spacer was sequenced for species identification (Bunikis et al., 2004). 3. Conclusions The natural reserve “Sierra del Sueve” is densely inhabited by ticks. Results of dragging showed a nymph abundance index of 24.3 in 2012 and 60.1 in 2013 mainly due to I.ricinus species but also to Haemaphysalis punctata and H. concinna. Other tick species (H. inermis, Dermacentor reticulatus, Rhipicephalus bursa), were collected less frequently. Borrelia burgdorferi s.l. was detected from 3.3-7.7% nymphs collected in 2010, 0.5-2.7% in 2011, 1.0-5.0% in 2012, 0.5-2.7% in 2013 and 0.5-2.7% in 2013, as well as in 12.5% of adults collected in 2011 and 4.8% in 2012. Borrelia burgdorferi s.l. was also detected from 11.5% (3/26) small mammals. Two different genospecies (B. afzelli and B. garinii) were identified from the questing ticks. The detection of Borrelia burgdorferi s.l. among questing ticks and small rodents, as well as the tick abundance and the presence of large populations of wild and domestic animals, indicate that the risk of infection in this area is relevant. This is also in accordance with clinical reports of Lyme disease from local hospitals.