Ixodes ricinus ticks infected with the causative agent of Lyme disease, Borrelia burgdorferi sensu lato, have higher energy reserves

Ticks use their energy reserves to maintain their water balance, search for hosts and transmit tick-borne pathogens. However, the influence of tick-borne pathogens on the energy reserves of the tick vector has not been well studied. The relationship between Borrelia burgdorferi sensu lato (s.l.) infection status and fat content in questing Ixodes ricinus nymphs was examined. Nymphs were sampled from the field. Their body mass and fat content were measured, and their Borrelia genospecies infection status (using reverse line blot analysis), and spirochete load (using quantitative PCR) were analysed. Of the 900 nymphs tested, 21.2% were infected with a variety of Borrelia genospecies. Borrelia-infected nymphs had 12.1% higher fat content than uninfected ticks after correcting for body size. For the subset of Borrelia-infected nymphs, no relationship was found between spirochete load and fat content and bioenergetics calculations suggest that Borrelia spirochetes consume a negligible fraction of the tick energy reserves. While the mechanism that causes the association between Borrelia infection and higher fat content in I. ricinus nymphs remains unknown, the present study complements our previous findings that Borrelia-infected nymphs had higher survival times under desiccating conditions and walked less within a humidity gradient.

Characterization of reptile-associated Borrelia sp. in the vector tick, Amblyomma geoemydae, and its association with Lyme disease and relapsing fever Borrelia spp

The genus Borrelia is arthropod-borne infectious agents in vertebrates, and is classified into Lyme disease (LD) Borrelia spp. and Relapsing fever (RF) Borrelia spp. In addition to these Borrelia groups, we recently reported reptile-associated (REP) Borrelia spp. from reptiles and from hard-bodied ticks, which probably transmitted the REP Borrelia spp. In this study, we investigated the presence of REP Borrelia sp. in moulted ticks, and found that trans-stadial transmission of REP Borrelia sp. occurred in the midgut, while it was observed that REP Borrelia sp. entered the salivary gland during blood-feeding. This characteristic is also found in LD Borrelia spp., which are also transmitted by hard-bodied ticks. Although phylogenetic analysis demonstrated that REP Borrelia spp. are similar to RF Borrelia spp., the ecology of the spirochaetes within the vector ticks is different for REP Borrelia spp. and RF Borrelia spp. Elucidation of the evolutionary history of the genus Borrelia and its adaptation to ticks promises to be of great interest to researchers of vector-borne microorganisms.

Données fondamentales à la base des mesures préventives

Lyme Borreliosis is the most common tick-transmitted disease in North America and Europe. Borrelia burgdorferi sensu lato causes Lyme disease and is transmitted by a tick belonging to Ixodes genus. The risk of tick-borne infection depends on the ecology of ticks. The risk of human infection depends on the density of the tick population and its infection rate. The aim of this manuscript is to review the ecology of Ixodes ricinus the main vector of Lyme disease in Western Europe, the reservoir hosts, and studies on locations of Ixodes and Borrelia in France. Ixodes ricinus is widely distributed over the French territory except in Mediterranean areas and land above than 1,500 m.

Complementation of a Borrelia afzelii OspC mutant highlights the crucial role of OspC for dissemination of Borrelia afzelii in Ixodes ricinus

Alteration of the outer surface protein (Osp) composition--especially that of OspA and OspC--seems to be important for the adaptation of Borrelia burgdorferi sensu lato to its endothermic hosts (mammals) and poikilothermic vectors (ticks). OspA possibly mediates adherence to tick midgut cells thus enabling the borreliae to survive in the vector, while OspC is associated with borrelial invasion of the tick salivary glands and infection of the mammalian hosts. Here we describe the first successful transformation and complementation of a Borrelia afzelii ospC mutant with the wild-type ospC in trans. To test the influence of OspC on the dissemination behavior in ticks, unfed Ixodes ricinus nymphs were artificially infected by capillary feeding either with B. afzelii wild type, the B. afzelii ospC mutant or the ospC-complemented clone. Tick midguts and salivary glands were investigated after different time intervals for the presence of borreliae and for OspA and OspC by immunfluorescence staining with monoclonal antibodies. While the B. afzelii wild-type strain exhibiting abundant OspC on its surface disseminated to the salivary glands, the OspC-negative mutant was only present in the tick midguts. The ospC-complemented clone which constitutively expresses the wild-type ospC was again able to colonize the salivary glands. This finding demonstrates that OspC is crucial for dissemination of B. afzelii from the tick midgut to the salivary glands, a prerequisite for infection of the warm-blooded host. A summary of the detailed data presented here has already been given in Goettner et al. [2006. OspC of B. afzelii is crucial for dissemination in the vector as shown by transformation and complementation of a European OspC-deficient B. afzelii strain. Int. J. Med. Microbiol. 296S1(Suppl. 40), 122-124].

Transstadial and transovarial persistence of Babesia divergens DNA in Ixodes ricinus ticks fed on infected blood in a new skin-feeding technique

Although Babesia divergens is the the principal confirmed zoonotic Babesia sp. in Europe, there are gaps in our knowledge of its biology and transmission by the tick Ixodes ricinus. In order to reproduce the part of the parasite cycle that occurs in the vector, an in vitro animal skin feeding technique on blood containing in vitro cultivated B. divergens was developed. Parasite DNA was detected in all samples of salivary glands of nymphs and adults that had fed on parasitized blood as larvae and nymphs, respectively, indicating acquisition as well as a transtadial persistence of B. divergens. PCR performed on eggs and larvae produced by females that had fed on parasitized blood demonstrated the existence of a transovarial transmission of the parasite. Gorging B. divergens infected larvae on non-infected gerbils showed persistance of the parasite over moulting into the resulting nymphs. These results indicate that the parasitic stages infective for the vector (i.e. the sexual stages) can be produced in vitro. To our knowledge, this is the first report of artificial feeding of I. ricinus via membrane as well as in vitro transmission of B. divergens to its vector. The opportunities offered by the use of such a transmission model of a pathogen by I. ricinus are discussed.

Lyme borreliosis in Europe and North America

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 compriseBorrelia burgdorferisensu 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 theIxodesticks 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.

The burgeoning molecular genetics of the Lyme disease spirochaete

Lyme disease is the most commonly reported vector-borne disease in North America and Europe, yet we know little about which components of the causative agent, Borrelia burgdorferi, are critical for infection or virulence. Molecular genetics has provided a powerful means by which to address these topics in other bacterial pathogens. Certain features of B. burgdorferi have hampered the development of an effective system of genetic analysis, but basic tools are now available and their application has begun to provide information about the identities and roles of key bacterial components in both the tick vector and the mammalian host. Increased genetic analysis of B. burgdorferi should advance our understanding of the infectious cycle and the pathogenesis of Lyme disease.

Investigations on the mode and dynamics of transmission and infectivity of Borrelia burgdorferi sensu stricto and Borrelia afzelii in Ixodes ricinus ticks

Borrelia burgdorferi sensu lato (sl), the agent of Lyme disease, is transmitted to the host during the blood meal of Ixodes ticks. In most unfed ticks, spirochetes are present in the midgut and migrate during blood feeding to the salivary glands, from which they are transmitted to the host via saliva. In the present study, the efficiency of Ixodes ricinus ticks to transmit B. afzelii and B. burgdorferi sensu stricto (ss) and their infectivity for mice were examined in relation to the duration of the blood meal. In addition, we investigated whether these two Borrelia species can penetrate intact skin. Three modes of infection of mice were studied: tick-bite infection, inoculation of tick homogenates, and transcutaneous infection by topical application of tick homogenates on mouse skin. Transmission of B. burgdorferi sl from I. ricinus nymphs to mouse increased with duration of tick attachment. B. afzelii-infected ticks start to transmit infection earlier (< or = 48 h) than B. burgdorferi ss-infected ticks. As previously shown for B. burgdorferi ss in Ixodes scapularis, B. burgdorferi ss and B. afzelii in unfed I. ricinus were noninfectious for mice when tick homogenates were inoculated. However, the inoculation of homogenates of ticks fed for 24 h readily produced infection in mice. Therefore, B. burgdorferi ss and B. afzelii spirochetes are potentially infectious in the tick before natural transmission can occur. None of the mice (n = 33) became infected by transcutaneous transmission when tick homogenates were applied on mouse skin, showing that B. burgdorferi ss and B. afzelii are unable to penetrate intact skin, in contrast to relapsing fever spirochetes. This study also shows that B. afzelii is transmitted by I. ricinus to the host earlier than B. burgdorferi ss and that I. ricinus seems to be a more efficient vector of B. afzelii than B. burgdorferi ss.

Glass capillary tube feeding: a method for infecting nymphal Ixodes scapularis (Acari: Ixodidae) with the lyme disease spirochete Borrelia burgdorferi

We evaluated an artificial capillary feeding method to infect nymphal Ixodes scapularis (Say) ticks with Borrelia burgdoeferi, the causative agent of Lyme disease. Thirty to 70% of the nymphs were infected after feeding for 2.5 h from glass capillary tubes filled with a solution of spirochetes. Capillary infection was stable and persisted in the nymphs for at least 10 d after feeding. Capillary feeding also maintained natural vector competence patterns because I. scapularis ticks acquired infection unlike Dermacentor variablis (Say), which did not become infected. Capillary infected I. scapularis nymphs were capable of transmitting the infection to naive mice although not as efficiently as naturally infected nymphs. The capillary infection method is convenient and is a better alternative to syringe inoculation as a means of infecting animals with B. burgdorferi.

Complement-mediated killing of Borrelia burgdorferi by nonimmune sera from sika deer

Various species of cervid deer are the preferred hosts for adult, black-legged ticks (Ixodes scapularis and Ixodes pacificus) in the United States. Although frequently exposed to the agent of Lyme disease (Borrelia burgdorferi), these animals, for the most part, are incompetent as transmission reservoirs. We examined the borreliacidal activity of normal and B. burgdorferi-immune sera from sika deer (Cervus nippon) maintained in a laboratory setting and compared it to that of similar sera from reservoir-competent mice and rabbits. All normal deer sera (NDS) tested killed > 90% of B. burgdorferi cells. In contrast, normal mouse and rabbit sera killed < or = 22% of the Borrelia. Anti-B. burgdorferi antibodies could not be detected in any normal sera by indirect fluorescent antibody assay (IFA). Sera collected from deer 6 wk after exposure to B. burgdorferi by tick feeding exhibited IFA titers of 1:256, whereas sera from mice and rabbits similarly exposed had titers of > 1:1,024. Heat treatment (56 C, 30 min) of NDS reduced borreliacidal activity, with < 20% of the B. burgdorferi cells killed, suggesting complement-mediated killing. The chelators EGTA and EDTA were used to block the classical or both the classical and alternative complement pathways, respectively. Addition of 10 mM EGTA to NDS had a negligible effect on borreliacidal activity, with > 90% of the cells killed. Addition of 10 mM EDTA reduced the killing to approximately 30%, whereas the addition of Mg2+ (10 mM) restored borreliacidal activity to NDS. The addition of zymosan A, an activator of the alternative pathway, increased the survival of B. burgdorferi cells to approximately 80% in NDS. These data suggest that the alternative complement activation pathway plays a major role in the borreliacidal activity of NDS. Additionally, 10 mM EGTA had almost no effect on the killing activity of B. burgdorferi-exposed deer sera, suggesting that the classical pathway is not involved in Borrelia killing, even in sera from B. burgdorferi-exposed deer.

Inhibition of Borrelia burgdorferi migration from the midgut to the salivary glands following feeding by ticks on OspC-immunized mice

Borrelia burgdorferi-infected ticks were fed on either OspC-immunized mice or normal, nonimmunized mice. After 72 h, the ticks were detached, followed by dissection and subsequent culturing in Barbour-Stoenner-Kelley II medium of the salivary glands from each tick to determine the presence of borreliae. Forty percent (10 of 25) of salivary glands from ticks that had fed on nonimmunized mice were culture positive, while only 7.4% (2 of 27) of salivary glands from ticks that had fed on OspC-immunized mice were culture positive, thus indicating a much reduced borrelial migration from the midgut when the bloodmeal contained anti-OspC antibodies. Fluorescent antibody staining of the corresponding midguts from ticks that had fed on the OspC-immunized mice showed that borreliae were present but did not produce OspC. In contrast, borreliae in midguts from ticks that had fed on normal mice demonstrated substantial ospC expression. This study provides evidence that, during tick feeding on an OspC-immunized host, transmission of borreliae from the tick is prevented; it also suggests that OspC functions in a tick-to-host transmission mechanism.

Effects of environmental pH on membrane proteins in Borrelia burgdorferi

Borrelia burgdorferi, the causative agent of Lyme disease, alternates between the microenvironments of the tick vector, Ixodes scapularis, and a mammalian host. The environmental conditions the spirochete encounters during its infectious cycle are suspected to differ greatly in many aspects, including available nutrients, temperature, and pH. Here we identify alterations in the membrane protein profile, as determined by immunoblotting and two-dimensional nonequilibrium pH gradient gel electrophoresis (2D-NEPHGE), that occur in virulent B. burgdorferi B31 as the pH of the medium is altered. Initial comparisons of cultures incubated at pHs 6.0, 7.0, and 8.0 yielded alterations in the expression of seven membrane proteins as determined by probing with hyperimmune rabbit serum. Six of these membrane proteins (54, 45, 44, 43, 35, and 24 kDa) were either present in increased amounts in or solely expressed by cultures incubated at pHs 6.0 and 7.0. The 24-kDa protein that decreased in expression at pH 8.0 was identified as outer surface protein C (OspC). In addition, a 42-kDa membrane protein increased in amount in cultures incubated at pH 8.0. Similar changes were observed with serum from a mouse infected by tick bite, with the recognition of two additional bands (48 and 46 kDa) unique to pHs 6. 0 and 7.0. When membrane fractions were analyzed by 2D-NEPHGE, at least 37 changes in the membrane protein profile between cells incubated at pHs 6.0, 7.0, and 8.0 were observed by immunoblotting and silver staining. Environmental cues such as pH may prove important in the regulation of virulence determinants and factors necessary for the adaptation of B. burgdorferi to the tick or mammalian microcosm.

Detection and typing of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks attached to human skin by PCR

Live Ixodes ricinus ticks attached to humans residing in Germany were examined for borreliae by dark-field microscopy and PCR. Borrelia species were identified by 16S rRNA sequence analysis, which showed the presence of several species, some not yet defined, and a high prevalence of multiply infected ticks.

Borrelia burgdorferi erp proteins are immunogenic in mammals infected by tick bite, and their synthesis is inducible in cultured bacteria

Borrelia burgdorferi, the causative agent of Lyme disease, can contain multiple genes encoding different members of the Erp lipoprotein family. Some arthropod-borne bacteria increase the synthesis of proteins required for transmission or mammalian infection when cultures are shifted from cool, ambient air temperature to a warmer, blood temperature. We found that all of the erp genes known to be encoded by infectious isolate B31 were differentially expressed in culture after a change in temperature, with greater amounts of message being produced by bacteria shifted from 23 to 35 degrees C than in those maintained at 23 degrees C. Mice infected with B31 by tick bite produced antibodies that recognized each of the Erp proteins within 4 weeks of infection, suggesting that the Erp proteins are produced by the bacteria during the early stages of mammalian infection and may play roles in transmission from ticks to mammals. Several of the B31 Erp proteins were also recognized by antibodies from patients with Lyme disease and may prove to be useful antigens for diagnostic testing or as components of a protective vaccine.

Expression of outer surface proteins A and C of Borrelia afzelii in Ixodes ricinus ticks and in the skin of mice

Several studies have described changes in the expression of proteins, especially of OspA and OspC, of B. burgdorferi sensu stricto during tick feeding. In this study, the expression of OspA and OspC of B. afzelii in unfed and feeding I. ricinus nymphs and in the subsequent adults was followed by means of the immunofluorescence test. Spirochaetes expressing OspA and OspC were observed in 70% and 80%, respectively of the unfed nymphs. In feeding and in fully engorged ticks, spirochaetes expressed OspC, while OspA disappeared 24 hours after the beginning of the blood meal. Spirochaetes expressing OspC in salivary glands were observed in one engorged tick. After molting, in unfed adults spirochaetes again expressed OspA and OspC but did so less frequently (6% and 13%, respectively). The mouse strain (AKR/N or BALB/C) on which ticks had their infectious blood meal influenced OspC expression in the following tick stage. In the skin of AKR/N mice, at the tick feeding site, B. afzelii expressed OspC only, as was shown by immunostaining.

Risk of infection with Borrelia burgdorferi sensu lato for a host in relation to the duration of nymphal Ixodes ricinus feeding and the method of tick removal

The objectives of the present study were to investigate the risk of B. burgdorferi s.1. (Bb)-transmission by I. ricinus-nymphs to a host (i) after different periods of feeding, and (ii) with regard to the particular method of tick removal. On each of 72 Mongolian gerbils 3 tick nymphs taken from a highly infected batch were allowed to feed in a small capsule. Feeding ticks were removed 16.7, 28.9, 47.0, and 65.2 hrs post-attachment. In each of these 4 groups 3 sub-groups with 6 gerbils each were deticked by (a) pulling ticks out with forceps without any pretreatment, (b) pulling ticks out after 3 min of intensive squeezing, and (c) applying nail polish to ticks 1.1 hrs before removal. The infection status in each gerbil was subsequently determined by larval xenodiagnosis. All gerbils with ticks removed > or = 47 hrs post-attachment were found to be infected. After 16.7 hrs as well as after 28.9 hrs of tick feeding, approximately 50% of the gerbils had acquired a transmissible infection, thus Bb-transmission to a host may even occur in the early phases of I. ricinus feeding. There is no evidence from this study that the tick removal method used has any significant influence on a host's Bb-infection risk.

Vaccination of natural reservoir hosts with recombinant lipidated OspA induces a transmission-blocking immunity against Lyme disease spirochaetes associated with high levels of LA-2 equivalent antibodies

As observed in humans, immune responses in naturally infected reservoir hosts of Borrelia burgdorferi sensu lato rarely target the outer surface proteins (Osp) A and B of Lyme disease spirochaetes. The absence of protective immunity in such hosts following tick-borne infection allows them to play an effective role in the maintenance of Lyme borreliosis in nature. Therefore, the question was addressed whether one of the most prominent natural reservoir host species of B. burgdorferi s.l. in Europe, the yellow-necked mouse (Apodemus flavicollis), may lack the ability to elicit transmission-blocking antibodies to Lyme borreliosis spirochaetes. Yellow-necked mice were immunized with a recombinant lipidated OspA from B. burgdorferi sensu stricto or with high numbers of UV-irradiated whole spirochaetes. All immunized mice, but not untreated controls, developed polyclonal humoral immune responses to OspA (31 kDa). Serum antibodies of animals vaccinated with the recombinant OspA contained high levels of antibody to an epitope of OspA, defined by the monoclonal antibody LA-2, whereas only low levels of LA-2 equivalent antibodies could be detected in sera from animals immunized with killed spirochaetes. Ixodes ricinus ticks infected with B. burgdorferi s.s. lost their spirochaete load after feeding on animals with high levels of LA-2 equivalent antibody; ticks feeding on animals which had only low or undetectable serum levels of LA-2 equivalent antibodies retained their spirochaete infection. Furthermore, animals with high levels of LA-2 equivalent antibody were protected against spirochaete infection. Our study shows that natural mouse reservoir hosts are highly competent to generate transmission-blocking antibodies after vaccination with a lipidated recombinant OspA and indicates that antibodies to the LA-2 epitope play a key role in the destruction of B. burgdorferi s.s. within feeding Ixodes ricinus ticks.

Dynamics of Borrelia burgdorferi infection in nymphal Ixodes ricinus ticks during feeding

We report the sequential development events of Borrelia burgdorferi in histological sections of Ixodes ricinus nymphs before, during and after feeding. During the blood meal a decrease of approximately 50% in the number of infected ticks was recorded (eight out of 76, 11%) in comparison with the infection rate of unfed ticks (12 out of 56, 21%). Spirochetes were detected in tick salivary glands only after 2 days of attachment. From day 3 until drop-off, the number of infected ticks increased to 31% (15 out of 49). A quadratic logistic regression analysis showed that the variation in the number of infected ticks was significant, but only during the blood meal. The drop in the percentage of infected ticks during the first hours following attachment to the host is explained by our observation of spirochetes in the faces of the ticks. The increase in the infection rate of replete ticks may be due to an uptake of spirochetes from the host skin at the feeding site.

Tick factors and in vitro cultivation influence the protein profile, antigenicity and pathogenicity of a cloned Borrelia garinii isolate from Ixodes ricinus hemolymph

A Borrelia garinii isolate (NE11H) was obtained from the hemolymph of infed Ixodes ricinus. NE11H expressed four major proteins of 33 kDa, 32 kDa, 23 kDa and 22 kDa. During in vitro culture, NE11H successively lost the expression of the 22 kDa and 23 kDa proteins and the NE11H variant (NE11Hp15) was not recognized by an immune serum specific for the OspC protein (anti-OspC IS). However, when reintroduced into tick midguts, NE11Hp15 spirochetes present in the midgut again reacted with anti-OspC IS. A clone derived from the wild type line, cNE11H, lacked the 22 kDa but not the 23 kDa protein. The 23 kDa protein of cNE11H was recognized by anti-OspC IS. In addition, the two descendant lines (NE11Hp15 and cNE11H) lost their capacity to induce clinical arthritis in SCID mice. When cNE11H was reintroduced into ticks and reisolated from various tick organs, most reisolates presented the same reaction with anti-OspC IS as cNE11H. Interestingly, two reisolates obtained from the tick midgut reexpressed large amounts of the 22 kDa protein which was recognized by anti-OspC IS and these two reisolates induced clinical arthritis in SCID mice. The results confirm that proteins of 22/23 kDa are differentially expressed during in vitro subcultures and in ticks, and show that proteins which are not detectable after in vitro culture may be reexpressed after reexposure of B. burgdorferi to its former environment in the tick. The data suggest that the pathogenicity of B. burgdorferi for mice might be influenced by environmental factors via differential expression of 22/23 kDa proteins.

Temperature-related differential expression of antigens in the Lyme disease spirochete, Borrelia burgdorferi

Previous studies have demonstrated that Borrelia burgdorferi in the midguts of infected ticks shows increased expression of the antigenic outer surface protein OspC after the ticks have ingested a blood meal. This differential expression is at least partly due to a change in temperature, as an increase in OspC levels is also observed when cultures are shifted from 23 to 35 degrees C. Immunoblotting of bacterial lysates with sera from infected mice indicated that the levels of several additional antigens were also increased in bacterial cultures shifted to 35 degrees C; we have identified one antigen as OspE. We have also observed differential expression of OspF, which has been proposed to be coexpressed in an operon with the gene encoding OspE.

Differential immune responses to Borrelia burgdorferi in European wild rodent species influence spirochete transmission to Ixodes ricinus L. (Acari: Ixodidae)

Immune responses to Borrelia burgdorferi and their influence on spirochete transmission to Ixodes ricinus were analyzed in the natural European reservoir hosts; i.e., the mouse species Apodemus flavicollis (yellow-necked mouse) and Apodemus sylvaticus (wood mouse) and the vole species Clethrionomys glareolus (bank vole), and, in addition, in the laboratory mouse strain NMRI. Naive and preimmunized rodents were infected either by artificially infected I. ricinus larvae or by intradermal injection of spirochetes. Independent of the species, all animals developed antibodies to various spirochetal antigens. However, antibodies to the outer surface proteins A (OspA) and B (OspB) were not found in recipients infected via ticks. Rodents of the genus Apodemus and of the NMRI strain showed higher levels of B. burgdorferi-specific antibodies than those of the species C. glareolus. The rate of spirochete transmission to noninfected ticks correlated with both the quality and quantity of spirochete-specific antibodies generated in the various species: high levels of spirochete-specific immunoglobulins correlated with low transmission rates. Furthermore, lower transmission rates were observed with rodents expressing antibodies to OspA and OspB (i.e., intradermally infected or immunized) than with those lacking these specificities (i.e., infected via ticks). The study provides evidence that transmission of B. burgdorferi from natural hosts to ticks is controlled by the specificity and quantity of spirochete-reactive antibodies and suggests that immunity to B. burgdorferi in natural reservoir hosts is an important regulatory factor in the horizontal transmission of B. burgdorferi in nature.

Characterization of Borrelia burgdorferi isolated from different organs of Ixodes ricinus ticks collected in nature

Borrelia burgdorferi was isolated from 22 out of 133 adult Ixodes ricinus ticks collected from vegetation at two sites in Switzerland. From 17 ticks, spirochetes could be isolated from more than one organ. When the different isolates obtained from one tick were compared by SDS-PAGE analysis, differences in the protein profiles were observed in 8 cases. The isolates were further compared by immunological methods using mono- and polyclonal antibodies. Differences were observed in the proteins of 31-35 kDa and 18-25 kDa. Genetic divergence among isolates was evaluated by use of a B. burgdorferi specific gene probe for ospA. Correlation could be observed between immunological differences in OspA defined by monoclonal antibody LA31 and genetic variation of ospA as judged by restriction fragment length polymorphism (RFLP). Our findings indicate that systemic infection in unfed I. ricinus adults, as reflected by isolation of B. burgdorferi from multiple organs of one tick, is more frequent (8/22, 36%) than previously described (5%). Moreover, the presence of different B. burgdorferi phenotypes/genotypes in one tick is described for the first time. The findings may have bearings (i) on the time of tick attachment required for spirochete transmission since borreliae are already present in the salivary glands of systemically infected ticks at the beginning of the blood meal and (ii) perhaps also on the diversity of B. burgdorferi phenotypes inoculated by these ticks.

Immunization of mice by recombinant OspA preparations and protection against Borrelia burgdorferi infection induced by Ixodes ricinus tick bites

The wide distribution of Borrelia burgdorferi, the spirochete causing Lyme borreliosis, represents a human health hazard in many areas of the world. Vaccination has been proposed as an effective prevention strategy. Vaccination experiments were conducted with preparations of recombinant outer surface protein A (OspA) derived from Borrelia burgdorferi strain ZS7. Mice received three doses (1 microgram each) of the antigens adsorbed to aluminum hydroxide. A strong immune response to the vaccine antigen was observed. Mice were challenged after immunization, using Ixodes ricinus nymphal ticks infected with Borrelia burgdorferi strain ZS7. Infection was investigated by ear biopsy culture, xenodiagnosis with uninfected larvae and serological response to Borrelia burgdorferi antigens. All unimmunized control animals were found to be infected, while all immunized animals were found to be protected against infection by Borrelia burgdorferi. In addition, most adult ticks derived from nymphs that fed on immunized mice were found to be free of spirochetes.

Ability of transovarially and subsequent transstadially infected Ixodes hexagonus ticks to maintain and transmit Borrelia burgdorferi in the laboratory

In a previous study, transstadial and transovarial survival of Borrelia burgdorferi in Ixodes hexagonus and transmission to laboratory mice via the bite of infected females were demonstrated. Here, we report the ability of I. hexagonus progeny infected transovarially to maintain and transmit the spirochaete to the host. Ticks were examined for spirochaetes by direct immunofluorescence antibody test. I. hexagonus larvae derived from the parental transstadially infected females were fed on two white mice: 21/54 (38.9%) of these ticks examined as unfed nymphs were infected. I. hexagonus nymphs were fed on three white mice and examined for spirochaetes after moulting as adults: 7/25 (28%) were found to harbour the spirochaete. The success of B. burgdorferi transmission to the mice by larval and nymphal I. hexagonus was determined by xenodiagnosis using I. ricinus larvae: 20/50 (40%) and 30/99 (30.3%) of the I. ricinus larvae fed on the mice infected by I. hexagonus larvae and nymphs respectively became infected. This study shows that B. burgdorferi can be maintained through transovarial and subsequent transstadial transmissions in I. hexagonus.

Changes in the protein profile and antigenicity of different Borrelia burgdorferi strains after reintroduction to Ixodes ricinus ticks

Eight Swiss strains of Borrelia burgdorferi, with various protein profiles and the North-American strain B31 were artificially introduced into Ixodes ricinus ticks and reisolated 10 days later. All isolates were subsequently examined by SDS-PAGE analysis. Comparing initial isolates with the reisolates, we observed that 7 out of 9 strains changed their protein pattern with respect to the major proteins OspA, OspB and the 22 kDa protein after passage in the tick. The strains NE2, NE4 and NE83 with the initial phenotype of OspA and 22 kDa proteins changed to the phenotype of OspA and OspB, the strains B2 and NE202 with the initial phenotype of OspA acquired an additional protein of 22 kDa and the strain NE58 with the initial phenotype of OspA also acquired a protein of 22 kDa. Examination of these isolates by Western blot analysis demonstrated that the reaction with the monoclonal antibody H5332 and a monospecific polyclonal antibody PoAb/anti-22 kDa differed between the initial isolates and the reisolates.

Ixodes (Pholeoixodes) hexagonus, an efficient vector of Borrelia burgdorferi in the laboratory

Borrelia burgdorferi Johnson et al. was first isolated from the midgut of Ixodes dammini Spielman et al. in the U.S.A. and from the midgut of I.ricinus (L.) in Europe. I.ricinus was considered to be the only tick vector of this borrelia, in Europe, until I.hexagonus Leach, the hedgehog tick, was found to harbour spirochaetes. This paper reports an evaluation of the vector competence of I.hexagonus for the spirochaete B.burgdorferi. Transovarial and trans-stadial survival were demonstrated and the spirochaete was transmitted to laboratory mice via the bites of trans-stadially infected I.hexagonus females.

The peritrophic membrane of Ixodes ricinus

A peritrophic membrane was found in all three stages of Ixodes ricinus at no later than 18 h after their placement on rabbits. It was found to remain intact until at least 11, 30 and 10 days after repletion in larvae, nymphs and females, respectively. In blood-feeding I. ricinus, the peritrophic membrane is an uneven single layer with a thickness of about 0.03-0.48 micron in larvae, 0.03-0.79 micron in nymphs and 0.04-0.93 micron in females. It covers the whole surface of the midgut epithelium at a distance of about 0.2-0.8 micron. After repletion, the peritrophic membrane becomes thicker and thicker and more and more winding and simultaneously becomes multi-layered mainly in its arched parts. The distance between the peritrophic membrane and the midgut epithelium increases considerably and in the arched parts can reach as much as about 13 and 16 microns in metamorphosing larvae and nymphs, respectively and 25 microns in ovipositing females.