The anticipated worldwide surge in urban environments is generating ever-greater interest in the study of host–pathogen interactions in this specific type of habitat. We investigated the potential of city-inhabiting rodents to serve as the main Lyme borreliosis agents (Borrelia spp.) reservoir. We also tried to verify if anthropogenic disturbances changing the vertebrate species community composition may also alter the scheme of Borrelia spp. circulation. A total of 252 Apodemus mice (A. agrarius, A. flavicollis, A. sylvaticus) were captured in Warsaw (Poland), at sites classified into different zones of anthropogenic disturbance, ranging from suburban forests to municipal parks strictly in the city centre. Borrelia spp. infection, ascertained based on bacterium DNA presence in the rodents’ blood, was found only in A. agrarius and A. flavicollis (7.6 and 6%, respectively). Only one species from the Borrelia genus – the mammal-associated species B. afzelii – was found in the mice studied. We found no statistical evidence of a correlation between infection in Apodemus mice and the zone of anthropogenic disturbance where the mice were caught. Non-homogeneous concentrations of Borelia spp. infected specimens within the strict city centre area suggest a lack of contact between members of particular mice subpopulations, and their responsibility for relatively high, but local Borrelia spp. infection.

To examine evidence of positive antibodies against immunogenic proteins of Anaplasma phagocytophilum in patients with other tick-borne infections and to diagnose possible co-infections, 412 serum specimens were tested by immunoblotting using three specific Anaplasma antigens: surface proteins p44 and Asp62 and outer membrane protein A (OmpA). In total, 284 serum samples from children with Lyme borreliosis and 12 serum samples from children with tick-borne encephalitis were tested. Sera from patients with viral aseptic meningitis (n = 47) and from blood donors (n = 69) were used as controls. Among all serum specimens from patients with tick-borne infections submitted for this study, six samples (2·0%) showed positive IgM reactions and seven samples (2·4%) were IgG positive for A. phagocytophilum by immunoblot. Borderline reactivity was found in 30 samples (10·14%) for IgM and 36 samples (12·2%) for IgG. The difference between patients and blood donors was statistically significant for IgM (P = 0·006) and for IgG (P = 0·0007) antibodies. A statistically significant result was obtained for IgG (P = 0·02) but not for IgM between patients and children with aseptic meningitis. Immunoblot using three specific antigens provides novel information about the positivity of antibodies to A. phagocytophilum in children with other tick-borne infections. Taking into account clinical and laboratory findings of children despite antibody positivity, no case of human granulocytic anaplasmosis was demonstrated.

Bird-specific ticks do not infest humans and livestock, but these ticks often share their avian hosts with generalist ticks that do. Therefore, their feeding activity may have an impact on the transmission of pathogens outside bird–tick transmission cycles. Here we examined the seasonal feeding activity of the tree-hole tick (Ixodes arboricola) in relation to the activity of its hole-breeding hosts (Parus major and Cyanistes caeruleus). We analysed data on ticks derived from birds, on the abundance of engorged ticks inside nest boxes, and on bird nests that were experimentally exposed to ticks. We observed a non-random pattern of feeding associated with the tick instar and host age. The majority of adult ticks fed on nestlings, while nymphs and larvae fed on both free-flying birds and nestlings. Due to their fast development, some ticks were able to feed twice within the same breeding season. The highest infestation rates in free-flying birds were found during the pre-breeding period and during autumn and winter when birds roost inside cavities. Except during winter, feeding of I. arboricola overlapped in time with the generalist Ixodes ricinus, implying that tick-borne microorganisms that are maintained by I. arboricola and birds could be bridged by I. ricinus to other hosts.

Since the discovery of the Lyme disease spirochete in North America in 1982 and in Europe in 1983, a plethora of studies on this unique group of spirochetes that comprise Borrelia burgdorferi sensu lato has been accumulated. In an attempt to compare and contrast Lyme borreliosis in Europe and North America we have reviewed the biology of the aetiologic agents, as well as the clinical aspects, diagnosis and treatment of this disease on both continents. Moreover, we have detailed the ecology of the Ixodes ticks that transmit this infection and the reservoir hosts that maintain the spirochete cycle in nature. Finally, we have examined the transmission dynamics of the spirochete on both continents, as well as the available prevention strategies. Although it has been over two decades since the discovery of the Lyme disease spirochete, Lyme borreliosis is an expanding public health problem that has defied our attempts to control it. By comparing the accumulated experience of investigators in North America and Europe, where the disease is most frequently reported, we hope to advance the cause of developing novel approaches to combat Lyme borreliosis.

This study deals with the ecology of Lyme borreliosis in Europe. The relationships between Borrelia burgdorferi sensu lato spirochetes, Clethrionomys and Apodemus rodent reservoirs and the Ixodes ricinus tick vector were investigated during 16 consecutive months in an enzootic area in Switzerland. Cultivation of ear skin biopsies was used to isolate spirochetes from C. glareolus, A. sylvaticus, A. flavicollis and Glis glis. Borrelia infection was more frequently observed in Clethrionomys than in Apodemus. Tick xenodiagnosis was used to determine the infectivity of rodents. The infection rate in ticks fed on Clethrionomys was higher than that in ticks fed on Apodemus, but Apodemus yielded more infected ticks than Clethrionomys because of a better tick moulting success. Xenodiagnostic ticks were placed into BSK medium to obtain isolates. Isolates from rodents and rodent-feeding ticks were all identified as B. afzelii. The follow-up of the infectivity status of repeatedly recaptured rodents clearly demonstrated that these hosts remained infective for ticks during winter till the following spring. Comparing C. glareolus and A. sylvaticus, each rodent species showed different host infection, different host infectivity and contributed differently to the moulting success of feeding ticks. These factors influence differentially the pattern of transmission of B. afzelii from Clethrionomys voles and Apodemus mice to I. ricinus ticks.

We present observational and experimental evidence that cycles of the Lyme disease spirochaete, Borrelia burgdorferi s.l., can be maintained by sheep in the virtual absence of alternative hosts. A 2-year field study in upland moorland habitats of northwest UK established that sheep feed up to 80% of larval, >99% of nymphal and all of the adult female tick (Ixodes ricinus) population. Infection prevalence of B. burgdorferi in questing ticks reaches over 20%, but amplification of infection occurs principally as nymphs (20- to 30-fold), rather than larvae (4- to 7-fold), feed on sheep, and transmission from sheep to ticks occurred only during peak tick abundance in May and September. Experimental transmission studies confirmed that sheep, previously exposed to infected ticks on the moorland site, do not support systemic infections of B. burgdorferi, but they can transmit localized infections from infected to uninfected ticks co-feeding at the same site on the sheep's body.