Identification of a New Borrelia Species among Small Mammals in Areas of Northern Spain Where Lyme Disease Is Endemic

Abstract

The role of small mammals as reservoir hosts for Borrelia burgdorferi was investigated in several areas where Lyme disease is endemic in northern Spain. A low rate of infestation by Ixodes ricinus nymphs was found in the small mammal populations studied that correlated with the near-absence of B. burgdorferi sensu lato in 184 animals tested and with the lack of transmission of B. burgdorferi sensu lato to I. ricinus larvae that fed on them. In contrast, questing ticks collected at the same time and in the same areas were found to carry a highly variable B. burgdorferi sensu lato repertoire (B. burgdorferi sensu stricto, Borrelia garinii, Borrelia valaisiana, and Borrelia afzelii). Interestingly, the only isolate obtained from small mammals (R57, isolated from a bank vole) grouped by phylogenetic analyses with other Borrelia species but in a separate clade from the Lyme disease and relapsing fever organisms, suggesting that it is a new species. This new agent was widely distributed among small mammals, with infection rates of 8.5 to 12% by PCR. Moreover, a high seroprevalence to B. burgdorferi sensu lato was found in the animal sera, suggesting cross-reactivity between B. burgdorferi sensu lato and R57. Although small mammals do not seem to play an important role as reservoirs for B. burgdorferi sensu lato in the study area, they seem to be implicated in the maintenance of spirochetes similar to R57.

Tick-Borne Zoonotic Bacteria in Wild and Domestic Small Mammals in Northern Spain

“…A. sylvaticus was clearly the most abundant species trapped over the two studies, indicating that this species is predominant in woodland areas of northern Spain, which is in agreement with reports from La Rioja, a neighboring region in north-central Spain (11). A. sylvaticus was also the rodent species most heavily infested with I. ricinus larvae and nymphs, in agreement with other reports from Europe (14,16,23). The different tick infection levels observed for different animal species (C. glareolus versus A. sylvaticus) were explained by acquired immunity to I. ricinus larvae after repeated infestations in C. glareolus (9).…”

“…This could be especially true when transovarial transmission of pathogens in ticks does not exist or occurs at a very low level and infection must be transmitted in the course of feeding by infected nymphs, as is the case for B. burgdorferi. However, the observed 72:1 ratio of larvae to nymphs was markedly lower than the one reported by Gil et al (14) in the same region (450:1), but the prevalence of B. burgdorferi sensu lato in small mammals was higher (0.8% in study 1 and 1.6% in study 2) than in the former study (0.5%), suggesting an increase in nymphal infestation in recent years. Interestingly, this is the first report of B. afzelii infection of small mammals in Spain and the first time that S. coronatus has been involved as a reservoir of Lyme borreliosis.…”

“…Samples positive for Borrelia spp. by multiplex PCR (16S rRNA gene) and RLB hybridization were analyzed using a PCR specific for B. burgdorferi sensu lato, targeting the 5S-23S rRNA intergenic spacer, followed by RLB hybridization with specific probes described previously (13,14,39,40) for B. burgdorferi sensu lato, B. burgdorferi sensu stricto, B. afzelii, B. garinii, B. valaisiana, and B. lusitaniae (Table 1). RLB hybridization was performed as previously described (14).…”

“…A limited number of small mammals from the same area was also analyzed for the presence of DNA of A. phagocytophilum, but all the specimens were negative (31). All these results were explained by the low number of Ixodes nymphs parasitizing small mammals in this area, with a 1:450 ratio of infestation of nymphs to that of larvae (14). The study area is particularly relevant due to the endemicity of Q fever pneumonia (29) and its proximity to an area where a new species of Rickettsia causing human disease, Rickettsia monacensis, has recently been identified in a patient (20a).…”

“…In Europe, several rodent species seem to be the natural reservoirs of Borrelia burgdorferi sensu lato (35), Anaplasma phagocytophilum (7,25), and C. burnetii (44), but there are few reports on the role of such species as possible reservoirs of tick-borne zoonotic bacteria in Spain. The role of small mammals in the biological cycle of B. burgdorferi sensu lato was recently investigated in areas of northern Spain where Lyme disease is endemic (14), and a low prevalence of infection was found (0.5%), but a new Borrelia sp. (Borrelia sp.…”