Borrelia burgdorferi sensu lato genospecies in questing Ixodes ricinus ticks in Austria

Unfed ticks of all instars (Ixodes ricinus, n=853; Haemaphysalis concinna, n=11) collected in all nine federal states of Austria were individually examined for the presence of Borrelia burgdorferi sensu lato (s.l.) using PCR. The mean overall infection rate was 14.4%. Infection rates were 24.5% in adult ticks, 16.1% in nymphs, and 1.6% in larvae. Four genospecies were detected, including B. valaisiana which was detected for the first time in Austria. The most common B. burgdorferi s.l. genospecies was B. garinii (66.9%), followed by B. valaisiana (13.7%), B. afzelii (11.3%), and B. burgdorferi sensu stricto (s.s.) (6.5%). Two specimens (1.6%) could not be identified to the genospecies level. Geographically, the highest infection rates were detected in the federal state of Vorarlberg (33.3%), B. garinii and B. afzelii being the most prevalent genospecies. B. valaisiana occurred most often in the federal state of Lower Austria, and B. burgdorferi s.s. was focally distributed in the Tyrol, in the surroundings of Imst.     

Efficiency of experimental infection of Ixodes ricinus ticks with Borrelia burgdorferi spirochetes

Feeding of an ixodid tick on a Borrelia-infected vertebrate is the natural route of tick infection. To obtain a cohort of nymphs with a high prevalence of infection, the immersion of Ixodes ricinus larvae in the suspension of B. burgdorferi sensu stricto spirochetes was used. Immersed larvae fed on C3H mice until full engorgement, molted to nymphs and 9 of 10 nymphs were shown to be infected by PCR with specific primers. Specific antibodies in the sera of the mice, on which either immersion-infected larvae or infected nymphs had engorged, were not detected. However, nymphs molted from immersed larvae were able to infect naïve mice, and all the resulting 10 adults were infected.     

Prevalence of Borrelia burgdorferi in Ixodes ricinus ticks in urban recreational areas of Helsinki

Lyme borreliosis, an infection caused by the tick-borne spirochete Borrelia burgdorferi, is a major health problem for populations in areas of endemicity in the Northern Hemisphere. In the present study we assessed the density of ticks and the prevalence of B. burgdorferi sensu lato among ticks in popular urban recreational areas of Helsinki, Finland. Altogether 1,688 Ixodes ricinus ticks were collected from five areas located within 5 km of the downtown section of Helsinki, and 726 of them (303 nymphs, 189 females, and 234 males) were randomly chosen for laboratory analysis. The midguts of the ticks were divided into three pieces, one for dark-field microscopy, one for cultivation in BSK-II medium, and one for PCR analysis. Ticks were found in all the study areas; their densities varied from 1 to 36 per 100 m along which a cloth was dragged. The rate of tick infection with B. burgdorferi sensu lato varied from 19 to 55%, with the average being 32%. Borellia afzelii was the most predominant genospecies in all the areas, and no B. burgdorferi sensu stricto isolates were detected. Only two ticks were concurrently infected with both B. afzelii and Borrelia garinii. Dark-field microscopy gave more positive results for B. burgdorferi than did cultivation or PCR analysis. However, the agreement between all three methods was fairly good. We conclude that Lyme borreliosis can be contracted even in urban environments not populated with large mammals like deer or elk. The disease should be taken into account in the differential diagnosis of certain symptoms of patients from these areas, and the use of measures to improve the awareness of the general population and health care officials of the risk of contracting the disease is warranted.     

Prevalence rates of Borrelia burgdorferi sensu lato in host-seeking Ixodes ricinus ticks in Europe

Borrelia burgdorferi sensu lato spirochetes have been found in all examined Ixodes ricinus (L.) populations in Europe. The overall mean proportions of unfed I. ricinus infected with B. burgdorferi s.l. were 1.9% (range 0–11%), 10.8% (2–43%) and 17.4% (3–58%) for larvae (n = 5699), nymphs (n = 48 804) and adults (n = 41 666), respectively. However, the results varied according to the method used. Cultivation in BSK medium is the least sensitive technique (an average of 11% adult ticks found infected), whereas polymerase chain reaction detecting spirochetal DNA is probably the most sensitive method (29% adults found infected). Microscopic methods (dark field, phase contrast, direct or indirect fluorescence) are generally comparable to each other (17–20% adults found infected) and should be regarded as standard procedures because they also make possible a quantitative estimation of spirochetes in the vector. Some technical problems of these methods are discussed. Received: 18 August 1997 / Accepted: 12 September 1997     

Prevalence of Borrelia burgdorferi s.l. in ticks feeding on humans in Thuringia/Germany

In 2004, a total of 618 Ixodes ricinus ticks fed on humans were collected by physicians throughout Thuringia. The prevalence rates of Borrelia burgdorferi sensu lato (s.l.) genotypes were determined by nested PCR and restriction fragment length polymorphism, targeting a 0.8-kb fragment of the ospA gene. The total prevalence of B. burgdorferi s.l. was 6.1%. B. afzelii was found in 67%, B. valaisiana in 15% and B. garinii in 15% of the positive ticks (3% could not be determined). In one tick, a double infection with B. valaisiana type II and B. garinii OspA type V was detected. Female adult ticks had the highest infection rate (11.7%), followed by nymphs (4.5%) and larvae (3.4%). The overall prevalence increased from spring (4.0%) to autumn (10.0%). Nevertheless, the risk of infection was maximal in summer, because of a much higher infestation and consequently a higher absolute number of infected ticks. The predominance of B. afzelii probably results from its resistance against human serum. The unexpectedly low total prevalence is possibly caused by immune defence mechanisms (e.g. complement) effective against less resistant B. burgdorferi s.l. strains in the tick.     

Prevalence of avian-associated Borrelia burgdorferi s.l. genospecies in Ixodes ricinus ticks collected from blackbirds (Turdus merula) and song thrushes (T. philomelos)

Between May and September of 2002, forest passerine birds and immature Ixodes ricinus ticks infesting them were surveyed for infection with Borrelia burgdorferi s.l. in a sylvatic habitat in west-central Poland. A total of 738 feeding I. ricinus ticks were recovered from 114 birds belonging to 9 species. The majority of ticks (65.7%) were collected from two thrush species, the blackbird (Turdus merula) and the song thrush (T. philomelos). Since only the two Turdus species proved to be parasitized by Borrelia-infected ticks, this study focused mainly on these birds. Immature ticks were removed from 53 of the 54 captured thrushes. A total of 304 partially or fully engorged ticks (110 larvae and 194 nymphs), and 53 bird-derived blood samples were tested for borreliae. B. burgdorferi s.l. DNA was detected by PCR in 11% of the larval ticks and in 7.2% of the nymphs. The PCR-positive ticks were found on 8 of 53 tick-infested thrushes. B. garinii and B. valaisiana accounted for 88.5% and 11.5% of the infections detected in Borrelia-positive ticks, respectively. Only one out of 53 of Turdus blood samples were PCR-positive for borreliae. The blood-positive thrush was infected with B. burgdorferi s.s. B. afzelii was the most frequently identified genospecies in PCR-positive questing I. ricinus ticks, followed by B. valaisiana (89% and 11%, respectively). The absence of B. afzelii infection in ticks feeding on passerine birds, despite its strong predominance in local questing nymph populations, indicates that avian hosts are not reservoirs of this genospecies and consequently that the rodent-adapted B. afzelii is negatively selected in ticks feeding on these hosts. These results validate the concept of some avian-associated genospecies within the B. burgdorferi s.l. complex and demonstrate that thrush species may support the circulation of B. garinii and B. valaisiana under natural conditions.     

Prevalence of Borrelia burgdorferi and Granulocytic and Monocytic Ehrlichiae in Ixodes ricinus Ticks from Southern Germany

A total of 287 adult Ixodes ricinus ticks, collected in two regions of southern Germany (Frankonia and Baden-Württemberg) where Borrelia burgdorferi infections are known to be endemic, were examined for the presence of 16S ribosomal DNA specific for the Ehrlichia phagocytophila genogroup, E. chaffeensis, E. canis, and B. burgdorferi by nested PCR. Totals of 2.2% (6 of 275) and 21.8% (65 of 275) of the ticks were positive for the E. phagocytophila genogroup and B. burgdorferi, respectively. Two ticks (0.7%) were coinfected with both bacteria. Of 12 engorged I. ricinus ticks collected from two deer, 8 (67%) were positive for the E. phagocytophila genogroup and one (8%) was positive for B. burgdorferi. There was no evidence of infection with E. canis or E. chaffeensis in the investigated tick population. The nucleotide sequences of the 546-bp Ehrlichia PCR products differed at one or two positions from the original sequence of the human granulocytic ehrlichiosis (HGE) agent (S.-M. Chen, J. S. Dumler, J. S. Bakken, and D. H. Walker, J. Clin. Microbiol. 32:589-595, 1994). Three groups of sequence variants were detected; two of these were known to occur in other areas in Europe or the United States, whereas one has not been reported before. Thus, in the German I. ricinus tick population closely related granulocytic ehrlichiae are prevalent, which might represent variants of E. phagocytophila or the HGE agent.     

Characterization of Borrelia burgdorferi sensu lato strains isolated from Ixodes ricinus in Mecklenburg-Vorpommern,Germany

Epidemiological studies in Mecklenburg-Vorpommern have shown a high prevalence ofBorrelia burgdorferi-infected ticks. A total of 17B. burgdorferi sensu lato strains were isolated from ticks and investigated by Western blots (immunoblot) with eight monoclonal antibodies against different epitopes of the outer surface protein A (OspA). Except for one, all strains could be classified using this system. The majority of strains belonged to theB. garinii-associated OspA serotypes 3, 5 and 6. Three isolates were classified as OspA serotype 2 (B. afzelii).B. burgdorferi sensu stricto strains (Ospa serotype 1) as well asB. garinii-associated OspA serotype 4 were not present.     

Borrelia burgdorferi infection prevalences in questing Ixodes ricinus ticks (Acari: Ixodidae) in urban and suburban Bonn, western Germany

From March to October 2003, a total of 2,518 host-seeking Ixodes ricinus ticks (1,944 nymphs, 264 females, 310 males) were collected by blanket dragging at 45 sites all over the city area of Bonn, western Germany, to be checked for Borrelia burgdorferi infection. The collection sites included 20 private gardens, nine public recreational parks, the boundaries of 14 sylvatic suburban areas and two footpaths between suburban farmed fields. Generally, numbers of specimens collected along sylvatic suburban areas and at urban sites with dense tree populations were significantly higher than at the other collection sites. Out of 1,394 specimens (865 nymphs, 241 females, 288 males) that were randomly chosen for Borrelia analysis by a simple PCR, 250 (17.9 %) were found to be infected with B. burgdorferi sensu lato. While the infection prevalences varied significantly between females (26.6%), males (12.5%) and nymphs (17.3%), there were no striking differences between sylvatic and unwooded sites. A total of 92.8% of the ticks Borrelia-positive by the simple PCR were also positive in a diagnostic nested PCR. Using genospecies-specific oligonucleotide probes, single Borrelia genospecies infections (91.4%) could be assigned to B. afzelii (39.5%), B. garinii (27.9%), B. burgdorferi sensu stricto (15.6%) and B. valaisiana (8.6%) by DNA hybridization. Various combinations of double infections were observed in 4.3% of the infected ticks. Another 4.3% of the Borrelia infections were untypeable. The B. burgdorferi genospecies distribution in the city area was shown to be variable from site to site and, even more, it was distinct from rural collection sites near Bonn. This is ascribed to a different spectrum of reservoir hosts. Taking into account the infection prevalences of host-seeking ticks in the forested surroundings of Bonn, our study demonstrates that the risk of acquiring Lyme disease after a tick bite in urban/suburban areas is comparably as high as in woodlands outside of the city.     

Determination of novel Borrelia genospecies in Swedish Ixodes ricinus ticks

A total of 301 adult questing Ixodes ricinus ticks were collected at 15 different locations along the south and east coasts of Sweden to determine the Borrelia genospecies diversity. Thirty-two ticks (11%) were found to be positive by nested PCR with Borrelia burgdorferi sensu lato-specific primers. Species determination was based on partial sequencing of the 16S rRNA gene and the flagellin gene. Five different Borrelia species were found. The nucleotide sequence of the Borrelia DNA found in two ticks differed extensively from the nucleotide sequences of the Borrelia DNA found in the other ticks, and analysis revealed that they were closely related to the relapsing fever borrelia species Borrelia miyamotoi. This is the first report of a B. miyamotoi-like borrelia in I. ricinus and in Europe. Moreover, the Borrelia DNA of two ticks (6%) clustered within the B. valaisiana complex. B. valaisiana has not previously been reported in Sweden. B. afzelii DNA was found in 14 ticks (44%), and B. garinii DNA was found in 10 ticks (31%). B. burgdorferi sensu stricto DNA was found in four ticks (13%). We conclude that all of the known human-pathogenic species (B. garinii, B. afzelii, and B. burgdorferi sensu stricto) and B. valaisiana found elsewhere in Europe are also present in the Swedish host-seeking tick population and that a B. miyamotoi-like Borrelia species seems to be present in I. ricinus ticks in Europe.     

Detection and identification of Anaplasma phagocytophilum, Borrelia burgdorferi, and Rickettsia helvetica in Danish Ixodes ricinus ticks

Borreliosis is an endemic infection in Denmark. Recent serosurveys have indicated that human anaplasmosis may be equally common. The aim of this study was to look for Anaplasma phagocytophilum and related pathogens in Ixodes ricinus ticks and estimate their prevalence, compared to Borrelia, using PCR. Ticks were collected from three locations in Denmark: Jutland, Funen, and Bornholm. Ticks from Jutland and Funen were analysed individually, ticks from Bornholm were analysed in pools of 20. A. phagocytophilum was found in ticks from all areas. A. phagocytophilum was found in 23.6% of ticks from Jutland and Funen, while 11% were positive for Borrelia burgdorferi. The Borrelia genotype B. afzelii was most prevalent, followed by B. valaisiana, B. burgdorferi s.s. and B. garinii.A. phagocytophilum was found in 14.5% of nymphs and 40.5% of adult ticks, while Borrelia was found in 13% of nymphs and 8% of adult ticks. The difference in prevalence between Anaplasma and Borrelia in adult ticks supports the idea that their maintenance cycles in nature may be different. Ticks were also infected with Rickettsia helvetica. Our study indicates that A. phagocytophilum prevalence in ticks in Denmark is as high as Borrelia prevalence and that human anaplasmosis may be unrecognized.     

Expression of outer surface proteins A and C of Borrelia burgdorferi in Ixodes ricinus ticks removed from humans

A total of 131 Ixodes ricinus (51 females, 1 male and 79 nymphs) removed from persons living in Southern Germany were investigated by immunofluorescence assay for the presence of Borrelia burgdorferi with a polyvalent rabbit immune serum and monoclonal antibodies specific for outer surface proteins (Osp) A or C. Borreliae were detectable in 48 (36.6%) of the ticks. Infection rates of these adults and nymphs were significantly higher than infection rates of unfed ticks from Southern Germany. Borreliae in 31.3% (n = 15) of the infected ticks expressed solely OspA, solely OspC in 12.5% (n = 6), and both OspA and OspC in 39.6% (n = 19) of ticks, while in 16.7% (n = 8) of ticks neither were expressed. Presentation of OspC by B. burgdorferi in I. ricinus was correlated with tick weight: in females, OspC was detectable only in ticks with a minimum weight of about 3.5 mg, and in nymphs weighing at least 1 mg. These results indicate that in I. ricinus removed from humans OspC is up-regulated during the blood meal of the tick, but in most ticks OspA is still detectable and might even be present in the absence of OspC expression in the midgut and salivary glands of nearly fully engorged nymphal ticks. Furthermore, we found strong evidence that borreliae expressing solely OspA while in the salivary glands can cause Lyme borreliosis. Our findings indicate that during tick feeding, humans are exposed to borreliae that may express either OspA or OspC or both, or lack both OspA and C. These findings suggests that, at the minimum, both OspA and C should be considered as vaccine candidates for prophylaxis of Lyme borreliosis in Europe. Received: 28 July 1998     

Coexistence of ehrlichiae of the phagocytophila group with Borrelia burgdorferi in Ixodes ricinus from Southern Germany

Human granulocytic ehrlichiosis (HGE) is an emerging infectious disease recognized in the Western hemisphere. HGE is well known to occur in North America, but records from outside the United States are sparse. The great majority of data from Europe are restricted to seroprevalence studies and molecular biological detection of granulocytic ehrlichiae (GE) in ticks and mammals, but include defined cases from Slovenia. They argue for the existence of this disease in many parts of Europe. In the present study, 510 Ixodes ricinus ticks collected in five different regions of Southern Germany were investigated for the presence of GE and Borrelia burgdorferi sensu lato using polymerase chain reaction. In all, 8 (1.6%) of the 492 ticks that could be evaluated (193 females, 208 males, and 91 nymphs) contained GE and 178 (36.2%) B. burgdorferi s.l.. Four of these ticks were infected with both pathogens. Interestingly, all ehrlichia-infected ticks were adults and all were collected in the English Garden, a recreational park area located in the city of Munich. Sequencing of the 16S rDNA (bp 1–1101) of four of the GE showed 100% sequence identity to each other and greater than 99.9% identity with the published sequence of the HGE agent. The four GE differed in respect to other hitherto described GE by a nucleotide exchange at position 336. These results show that GE that are closely related to the HGE agent are present in Southern Germany, and that coinfection with B. burgdorferi is common in GE-infected ticks. However, in contrast to B. burgdorferi which is endemic everywhere in Southern Germany, the distribution of GE seems to be focal. Received: 30 July 1999     

Genospecies of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks from the Autonomous Province of Trento, Italy

Sequences of the variable intergenic spacer region 5S (rrfA) 23S (rrlB) rRNA were used to identify Borrelia genospecies present in Ixodes ricinus nymphs collected from the Lamar Lakes area of the Province of Trento, Italy (overall prevalence=6.3%). Four genospecies were identified, one for the first time in this Province (B. valaisiana), and three which have been noted previously (B. afzelii, B. garinii, and B. burgdorferi s.s.). In order to compare the genetic variability of these genospecies in Trento with that at a European level, our 21 sequences (15 new haplotypes) and all appropriate European Borrelia sequences registered in GenBank (up to the end of 2004) were subjected to a phylogenetic analysis (for a total of 73 sequences and 43 haplotypes). Clusters of sequences representing the five main European genospecies (afzelii, garinii, burgdorferi s.s., valaisiana, lusitaniae) are well-supported. At least two other groups of haplotypes (genospecies) are suggested by our analysis; moreover, divergent evolution may be occurring in several genospecies. The maximum uncorrected pairwise differences between sequences within genospecies ranges from 1.5% (B. burgdorferi s.s.), to 2.3% (B. garinii and B. valaisiana) to 4.7% (B. afzelii), and are not correlated with geographical distribution. Within the Province of Trento, these values for the same genospecies are 1.5%, 2.3%, 0.9%, 1.9%, respectively. These high mutation rates within genospecies suggest that the sequencing of haplotypes should continue if we are to fully understand and monitor the evolution and epidemiology of Borrelia.     

Early detection of Borrelia burgdorferi sensu lato infection in Balb/c mice by co-feeding Ixodes ricinus ticks

In Europe, Borrelia burgdorferi is transmitted by Ixodes ricinus to animals and human. When infected and uninfected ticks co-feed on a host, spirochetes are transmitted from ticks to animal and also to uninfected ticks. Here, we used uninfected ticks to co-feed with infected ticks on mice to evaluate this method to detect early infection in mice. A total of 128 mice were challenged by infected nymphs placed in capsules glued on the back of the mice. Three days later uninfected larvae were added in the capsule to co-feed with infected nymphs and were examined for Borrelia infection after natural detachment. Infection in mice was also determined by xenodiagnosis and by spirochete isolation from ear skin biopsy and back skin biopsy taken at the tick attachment site one month after infection. A total of 111 mice were found to be infected by at least one of these four methods. Borrelia infection was observed in 95% of mice by the co-feeding method, in 92% of mice by xenodiagnosis, in 69% and in 68% of mice by cultivation of ear and back skin biopsies, respectively. Our results demonstrate that the co-feeding method is a very sensitive method which can be used to detect very early infection in mice infected by tick bites.     

Detection of three genospecies of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks collected in different regions of Poland

Ixodes ricinus ticks, collected in 1996-1998 in different Polish woodlands, were examined to assess the frequency of the occurrence of Lyme borreliosis-associated genospecies. A total of 568 samples of individual adults and 162 samples of individual (n =48) and pooled (of 2 to 7) samples of nymphs were analysed by the polymerase chain reaction (PCR) for Borrelia burgdorferi sensu lato. Spirochetes were detected in 130 adult ticks (22.9%) and in a minimum of 32 (5.3%) nymphs. Further identification of 153 B. burgdorferi s.l.-positive samples by nested PCR using three species-specific primers revealed the occurrence of B. afzelii, B. burgdorferi sensu stricto and B. garinii. Both single-species and mixed infections were noted. Single-species infections were observed in the majority of samples (n = 83/153; 54.2%). Within this group B. afzelii was found in 38/153 samples (24.9%), followed by B. burgdorferi sensu stricto (n = 23/153; 15.0%) and B. garinii (n = 22/153; 14.4%). Dual infections with B. burgdorferi s.s. and B. afzelii were detected in 17/121 (14.0%) adults, while both B. burgdorferi s. s./B. garinii and B. afzelii/B. garinii coinfected 11/121 (9.1%) adult ticks. Triple infection with B. burgdorferi s.s., B. afzelii and B. garinii was noted twice (1.6%). In general, B. afzelii was found in 72/153 (47.1%) tick samples and was the predominant species. B. burgdorferi s. s. and B. garinii were detected in a total of 60/153 (39.2%) and 51/153 (33.3%) samples, respectively. Although, 21 (13.7%) samples were infected by B. burgdorferi s.l. genospecies undetectable by the primers used, results of our study confirm that Lyme borreliosis pathogenic genospecies are well established in tick populations throughout Poland.     

Diversity in prevalence and genospecies of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks and rodents in Lithuania and Norway

A total of 1679 questing Ixodes ricinus ticks collected in Lithuania and 535 I. ricinus ticks collected in Norway from locations with different habitats were investigated for the presence of Borrelia burgdorferi sensu lato. In Lithuania, 223 ticks (13.3%) were infected with B. burgdorferi s.l., and in Norway, 28 ticks (5.2%). The highest prevalence of B. burgdorferi s.l was found in deciduous and mixed forests (19.4% in Lithuania, 8.6% in Norway). A lower prevalence was determined in pine forests (8.6% in Lithuania) and costal zones (4.3% in Norway), and the least prevalence was found in grasslands (2.5% in Lithuania, 1% in Norway). A total of 398 rodents belonging to 9 species were live-captured in Lithuania and Norway. Prevalence of B. burgdorferi s.l. in rodents varied between species and sampling sites in both countries. In Lithuania, the prevalence of infection was higher in Microtus arvalis (range 25–57% in different sampling sites) and in Myodes glareolus (range 14–71%) than in Apodemus flavicollis (range 0–37%) and in A. agrarius (range 11–33%). In Norway, the prevalence of B. burgdorferi s.l. in rodents was lower (range from 5% in A. sylvaticus to 6% in A. flavicollis). B. afzelii was the predominant genospecies in ticks and rodents in Lithuania and Norway. In Lithuania, B. afzelii was found in 76%, B. garinii in 10%, B. burgdorferi sensu stricto in 7%, and Borrelia spp. in 6% of infected ticks. Double infections were observed in 1% of the infected ticks. In Norway, B. afzelii was found in 68%, B. garinii in 21%, and B. burgdorferi s.s. in 11% of infected ticks. All infected rodents from both countries hosted B. afzelii genospecies. Only the red squirrel (Sciurus vulgaris) harbored both B. afzelii and B. burgdorferi s.s.     

OspA antibodies inhibit the acquisition of Borrelia burgdorferi by Ixodes ticks.

Ixodes ticks are infected by Borrelia burgdorferi when larvae feed on spirochete-infected mice. We studied the acquisition of B. burgdorferi by larval ticks, characterized the production of outer surface protein A (OspA) by spirochetes entering larvae, and examined the effects of OspA antibodies on the establishment of B. burgdorferi infections in ticks. Most larvae were infected by spirochetes 24 to 48 h after placement on mice. OspA antibodies stained the first spirochetes observed in larvae, suggesting that OspA is synthesized early during the colonization of the vector. When OspA antibodies were administered to B. burgdorferi-infected mice and larvae were then placed on the animals, the severity of larval infection and the number of infected ticks (7 of 16) were decreased compared with that of controls (15 of 16). The inhibitory effects of OspA antibodies were observed with passive antibody transfer as well as active host-generated immunity. The lower larval infection rate observed in the presence of OspA antibodies was exacerbated after the larval molt since only 1 of 12 nymphs was infected, and none of the mice that were fed upon by these nymphs became infected with B. burgdorferi. Therefore, an OspA antibody response in mice altered the reservoir competence of the vertebrate host by inhibiting the movement of B. burgdorferi from the host to the vector.