No abstract

A previous analysis of tick infestation patterns on rodents in Slovakia suggested that the key to the focal distribution of western-type tick-borne encephalitis virus (TBEv) in Europe is the geographically variable degree of synchrony in the seasonal activity of larval and nymphal Ixodes ricinus ticks. This prediction is here tested by examining records, from 7 different countries, of the seasonal variation in the abundance of larvae and nymphs feeding on rodents or questing on the vegetation. Larvae consistently started feeding and questing earlier in the year at sites within TBEv foci than elsewhere, so that they appeared in the spring as soon as nymphs were active. Such larval nymphal synchrony is associated with a rapid fall in ground-level temperatures from August to October as revealed by the satellite-derived index of Land Surface Temperature (LST). Likewise, of 1992 pixels sampled on a grid across Europe, the 418 that fell within TBEv foci were characterized by a higher than average rate of autumnal cooling relative to the peak midsummer LST. It is proposed that such a seasonal temperature profile may cause unfed larvae to pass the winter in quiescence, from which they emerge synchronously with nymphs in the spring.

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 questingIxodes 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 afzelii 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/orB. valaisiana. Although 19% of the rodents harboredB. burgdorferi sensu stricto and/or B. gariniiin 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.

The abilities of the most common European genospecies of Borrelia burgdorferi sensu lato to survive blood meals taken by ticks feeding on birds were analyzed. A pattern of differential survival of the spirochetes in feeding ticks was observed. The result is consistent with the concept of selective transmission of Lyme borreliosis spirochetes.The genospecies of Borrelia burgdorferi sensu lato and, at times, their variants are maintained in nature by different sets of hosts (1, 3, 6-10, 15, 18, 20, 21, 23; K. Hanincová, S. M. Schäfer, S. Etti, H.-S. Sewell, V. Taragelová, D. Ziak, M. Labuda, and K. Kurtenbach, submitted for publication). At present, the key determinant of this host association is considered to be the interaction of B. burgdorferi sensu lato with the alternative pathway of the host's complement system (14,16,19,22,25). A recently proposed model of transmission predicts the selection of spirochetes by complement in the gut of feeding ticks (17,18). In the present study, an avian model was used to test this prediction.Two-week-old pheasants (Phasianus colchicus) were obtained from a breeder in Oxfordshire, United Kingdom. Ixodes ricinus larvae and nymphs were derived from a tick colony maintained at the NERC Centre for Ecology and Hydrology, Oxford, United Kingdom. Low-passage cultures of B. burgdorferi sensu stricto (ZS 7), Borrelia afzelii (ACA 1), Borrelia garinii (an isolate from Freiburg, Germany, with an ospA allele identical to that of the Rio2 strain [2]), and Borrelia valaisiana (strain UK) were expanded to a concentration of 10 7 cells per ml of culture medium. The cultures were used to infect questing nymphs with spirochetes by glass capillary feeding. Of those ticks which took up more than 100 spirochetes, as calculated by the volume of culture imbibed, 20 were introduced to each bird by being confined within a neoprene cell glued with latex to the shaved throat of each bird (Fig.1). Four groups composed of four birds each were challenged with ticks infected with one of the genospecies of B. burgdorferi sensu lato. Engorged nymphs were recovered, kept for 2 weeks, and then preserved in 70% ethanol.For comparison, an additional four groups of 10 nymphs each (all of whom were preinfected with one of the four genospecies) were not allowed to feed on hosts but were starved for several weeks and then preserved in ethanol. Four weeks after the challenge with infected nymphs, the pheasants were tested by xenodiagnosis for Borrelia through the introduction of Ͼ50 noninfected I. ricinus larvae per animal. These larvae were also contained in neoprene cells and glued to the back of the neck of each pheasant. Engorged larvae were allowed to molt to nymphs. After xenodiagnosis, two skin biopsy samples were taken from each bird, one from the feeding site of ticks and one from the eyelid. The 5S-23S intergenic spacer and the ospA locus of B. burgdorferi sensu lato were amplified by nested PCR from DNA extracted from Borrelia cultures, ticks, and biopsy samples (5, 15), and the PCR products were sequence...