Differential transmission of the genospecies of Borrelia burgdorferi sensu lato by game birds and small rodents in England

Abstract

The genetic diversity of Borrelia burgdorferi sensu lato was assessed in a focus of Lyme borreliosis in southern Britain dominated by game birds. Ticks, rodents, and pheasants were analyzed for spirochete infections by PCR-targeting the 23S-5S rRNA genes, followed by genotyping by the reverse line blot method. In questing Ixodes ricinus ticks, three genospecies of B. burgdorferi sensu lato were detected, with the highest prevalences found for Borrelia garinii and Borrelia valaisiana. B. burgdorferi sensu stricto was rare (< 1%) in all tick stages. Borrelia afzelia was not detected in any of the samples. More than 50% of engorged nymphs collected from pheasants were infected with borreliae, mainly B. garinii and/or B. valaisiana. Although 19% of the rodents harbored B. burgdorferi sensu stricto and/or B. garinii in internal organs, only B. burgdorferi sensu stricto was transmitted to xenodiagnostic tick larvae (it was transmitted to 1% of the larvae). The data indicate that different genospecies of B. burgdorferi sensu lato can be maintained in nature by distinct transmission cycles involving the same vector tick species but different vertebrate host species. Wildlife management may have an influence on the relative risk of different clinical forms of Lyme borreliosis.

FIG. 1

Reverse line blot to identify the genospecies of B. burgdorferi sensu lato prevalent in ticks and host tissues. Lanes 1 to 4 contained positive controls that were PCR products of cloned isolates (lane 1, B. burgdorferi sensu stricto; lane 2, B. garinii; lane 3, B. afzelii; lane 4, B. japonica). The results for hybrids of representative PCR products from pheasant- and rodent-derived ticks and from tissues are also shown. Untypeable samples reacted with the B. burgdorferi sensu lato-specific DNA probe, but not with any of the genospecies-specific probes. Genomic group VS116 has recently been named B. valaisiana (39) and was not included as a positive control in the blot shown. Abbreviations: B. bu. s.l., B. burgdorferi sensu lato; B. bu. s.s., B. burgdorferi sensu stricto.