Previous Article | Next Article ![]()
Infect Immun, March 1998, p. 1248-1251, Vol. 66, No. 3
Department of Zoology,
Received 15 October 1997/Returned for modification 17 November
1997/Accepted 10 December 1997
The sensitivity of Borrelia burgdorferi sensu lato to
animal sera was analyzed. Complement-mediated borreliacidal effects were observed with particular combinations of host serum and
Borrelia genospecies. The species-specific pattern of
viability and/or lysis is highly consistent with the pattern of
reservoir competence of hosts for B. burgdorferi sensu
lato, suggesting a key role of complement in the global ecology of Lyme
borreliosis.
Borrelia burgdorferi, the
tick-borne agent of Lyme borreliosis, is a genetically diverse species
complex of spirochetes, comprising at least nine genospecies (22,
23, 31). The different genospecies of B. burgdorferi
sensu lato appear to cause distinct clinical manifestations of Lyme
borreliosis in humans (28). Consistent with this, arthritis
is common in North America, where B. burgdorferi sensu
stricto predominates, whereas in Eurasia, neuroborreliosis and
acrodermatitis are typical disease manifestations, reflecting the high
abundance of Borrelia garinii and Borrelia
afzelii throughout this region (5, 7, 16, 20, 25).
Other genospecies, such as Borrelia lusitaniae (former
genomic group PotiB2), Borrelia valaisiana (former genomic
group VS116), and Borrelia japonica from Japan or
Borrelia andersonii from the United States, have not yet
been associated with disease in humans. Geographic variation in the
distribution of different B. burgdorferi sensu lato
genospecies in regions where the same tick species is involved as the
vector, e.g., in Europe with Ixodes ricinus (10,
23-25), appears to be associated with host-specific differential
spirochete transmission between hosts and ticks. For example, recent
studies indicate that B. garinii and B. valaisiana are transmitted preferentially to ticks by certain
avian hosts while B. afzelii is transmitted preferentially
to ticks by European rodent species (6, 7, 14, 19). Although
it has been previously suggested that adaptive immune responses may be
involved in the regulation of spirochete transmission (11),
the mechanisms underlying differential transmission of the
Borrelia genospecies by hosts have so far been unknown.
Cultured spirochetes belonging to different genospecies of B. burgdorferi sensu lato differ in their sensitivity to human serum
(1, 29). To determine whether such a phenomenon plays a role
in spirochete transmission cycles, we analyzed the sensitivity of
different genospecies of B. burgdorferi sensu lato to sera from a wide range of reservoir-competent and -incompetent animals, including small mammals, lagomorphs, sheep, horses, cattle, pigs, deer,
and game birds.
The Borrelia strains ZS 7 (B. burgdorferi sensu
stricto), ACA-1 (B. afzelii), ZQ 1 (B. garinii),
HO 14 (B. japonica), and UK (B. valaisiana) were
cultured in BSK-II medium (Sigma) without the addition of serum or
antibiotics. The isolates were low passage and clonal. The taxonomic
identity and clonality of each isolate were confirmed by PCR
amplification of the intergenic spacer between the 5S and 23S rRNA
genes and subsequent genotyping by using the reverse line blot as
described previously (14, 23).
Sera were taken from adult wood mice (Apodemus sylvaticus),
BALB/c mice, bank voles (Clethrionomys glareolus), Syrian
hamsters, grey squirrels (Sciurus carolinensis), blue
mountain hares (Lepus timidus), sheep (lambs), horses, pigs,
cattle (cow and calf), red deer (Cervus elaphus), pheasants
(Phasianus colchicus), and a human. All sera, except those
from the human, hares, and horses, came from animals without any
previous contact with I. ricinus ticks. The following
noninfected animals were bred at the institutions indicated: small
rodents at the Department of Zoology, University of Oxford, and NERC
Institute of Virology and Environmental Microbiology, Oxford, United
Kingdom; pheasants at the Game Conservancy Trust, Fordingbridge, United
Kingdom; sheep (lambs), pigs, and cattle at the Department of
Veterinary Clinical Medicine, University of Liverpool, Liverpool,
United Kingdom; and deer at the Reediehill Deer Farm, Auchtermuchty,
United Kingdom.
For borreliacidal assays, Borrelia cultures were grown to an
approximate density of 107 cells per ml of culture medium
at 33°C without antibiotics under microaerophilic conditions. Sera
were thawed on ice shortly before use. Suspensions of
Borrelia cultures were added to variable concentrations of
serum to give final volumes of Borrelia-serum suspensions of 100 µl per well in 96-well microtiter plates (Nunc). Some aliquots of
sera were depleted of functional complement, or components thereof, by
heat treatment (0.5 h of incubation at 56°C) or by the addition of
either EDTA (10 mM) or MgCl2 (4 mM) plus EGTA (10 mM),
while other aliquots were left untreated. Controls consisted of
Borrelia cultures without any supplements. The plates were sealed and incubated at 33°C for mammalian sera and at either 33 or
38°C for avian sera. Three parameters of borreliacidal effects, each
known to be an indicator of Borrelia mortality
(29), were recorded: bleb formation, immobilization, and
bacteriolysis. Each well was read at 0, 2, 4, and 22 h. Ten
microliters of each suspension was collected aseptically and examined
by using dark-field microscopy.
After incubation for 22 h with a 50% final serum concentration, a
clear pattern of bacteriolysis was observed (Table
1). All rodent and human sera were
borreliacidal for B. garinii and B. valaisiana
but not for B. afzelii and B. japonica. In
contrast, all pheasant sera showed the reverse pattern, killing
B. afzelii and B. japonica but not B. garinii and B. valaisiana. Sera from wood mice and
pheasants were also partially borreliacidal for B. burgdorferi sensu stricto. The hare serum was borreliacidal for
the genospecies tested except for B. japonica. Most sheep sera were intermediately borreliacidal for B. burgdorferi
sensu stricto, B. afzelii, and B. japonica but
highly borreliacidal for B. garinii and B. valaisiana. The sera from horses, pigs, and cattle killed all of
the genospecies tested except for B. burgdorferi sensu
stricto, while the sera from red deer were indiscriminately borreliacidal for all of the genospecies tested. The pattern of Borrelia sensitivity to the human serum included in the
present study was consistent with that reported in earlier studies
(1, 29). Controls, including all of the Borrelia
strains, which were always incubated together with the test samples at
either 33 or 38°C, showed no genotype-specific difference in
temperature tolerance per se (data not shown). Furthermore, incubation
of bird serum and spirochetes at 33°C showed the same pattern of results as that observed at 38°C (data not shown). Thus, although the
body temperature of birds is higher than that of mammals, differences
in the temperature tolerance of spirochete strains cannot account for
the observed contrasting patterns of bacteriolytic activity of sera
from birds and rodents.
Borreliacidal effects became apparent within 2 h of incubation and
increased with time. For the selected combinations of wood mouse-B. garinii, sheep-B. burgdorferi sensu
stricto, red deer-B. garinii, and pheasant-B.
afzelii, the effect of the serum concentration on the kinetics of
killing was assayed (Table 2). Partial
effects were observed at a serum concentration of 10%, but all effects were more rapid and pronounced at the higher concentrations of 25 and
50%.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Serum Complement Sensitivity as a Key Factor in
Lyme Disease Ecology
![]()
ABSTRACT
Top
Abstract
Text
References
![]()
TEXT
Top
Abstract
Text
References
TABLE 1.
Bacteriolysis of different genospecies of B. burgdorferi sensu lato by untreated sera after 22 h
of incubation
TABLE 2.
Bacteriolysis of B. burgdorferi sensu lato by
different concentrations of untreated sera after 2, 4, and 22 h
of incubationa
Heat inactivation (0.5 h at 56°C) of sera from mice (n = 3), hares (n = 1), sheep (n = 4), cows (pool), bovine calves (pool), pigs (pool), deer (n = 4), and pheasants (n = 3) abolished all borreliacidal effects, indicating that the complement system is involved in the killing. When these sera were supplemented with EDTA, all borreliacidal effects were abolished in the same way as seen after heat inactivation, whereas supplementation with Mg-EGTA did not disrupt bacteriolysis (data not shown). These results indicate that the alternative pathway of the complement system, which operates independently of antibodies, plays a key role in spirochete killing (30). Thus, the bacteriolysis observed in the present study is distinct from the borreliacidal effects observed with immune sera (12, 21).
All genospecies of B. burgdorferi sensu lato are maintained in nature by tick-vertebrate transmission cycles. The pattern of species-specific, complement-mediated sensitivity to serum observed in the present study is highly consistent with the observations on spirochete transmission patterns reported so far. For example, the resistance of B. afzelii to rodent serum parallels the high level of transmission competence of both small natural rodent species (7) and squirrels (2) for this genospecies. In contrast, the particular B. garinii strain used in the present study, isolated in western Europe, was readily lysed by rodent sera. This is consistent with the finding that European rodents are inefficient reservoir hosts for the variants of B. garinii found in Europe, despite the fact that B. garinii has been isolated from or detected in rodent tissues (7, 14, 16, 17). Most interestingly in terms of evolution, B. garinii is a polymorphic genospecies of B. burgdorferi sensu lato (31), and there is evidence that one genotype of this genospecies, detected only in Japan so far, is efficiently transmitted by Japanese rodents to ticks (16). The resistance of the B. garinii strain tested against bird serum, on the other hand, is consistent with the finding that B. garinii has been associated with ticks derived from seabirds (19), blackbirds (6), and pheasants (13, 14). Likewise, blackbirds and pheasants, but not rodents, have been identified as reservoir hosts for B. valaisiana (6, 14). The finding that pheasant serum lysed B. afzelii, by comparison, may explain the incompetence of such birds as reservoirs for this genospecies. Sera from wood mice, but not from bank voles, were intermediately borreliacidal for B. burgdorferi sensu stricto, which is consistent with the lower degree of reservoir competence of wood mice for this genospecies compared with that of bank voles (11). Furthermore, the reported reservoir incompetence of deer (8, 27) correlates with the indiscriminatory borreliacidal activity of deer sera against all the genospecies tested. The reservoir competence for B. burgdorferi sensu lato of another ungulate species, sheep, appears to be low. However, it has been shown that transmission of B. burgdorferi sensu stricto from infected to uninfected ticks cofeeding on sheep may occur (18), perhaps related to the intermediate sensitivity of this genospecies to sheep serum.
In summary, the pattern of serum (complement) sensitivity of different Borrelia genospecies matches the known reservoir status of many vertebrate species for B. burgdorferi sensu lato. The hare, however, appears to be an exception since this species has been described to be reservoir competent for B. burgdorferi sensu lato in Scandinavia (26). The reason for the discrepancy between the pattern of serum compatibility and the reported reservoir status of hares remains unclear but may be related to the particular source of the serum (a hare from Scotland) and the strains of B. burgdorferi sensu lato used in the present study. At present, there is no information available on the reservoir competence of horses, pigs, and cattle for B. burgdorferi sensu lato. However, by extrapolating the findings of the present study, one may predict that horses, pigs (perhaps also wild boar), and cattle are reservoir competent, at a low level, for B. burgdorferi sensu stricto but not for any other genospecies analyzed in the present study.
Vertebrate hosts may be infected concurrently with different genospecies of B. burgdorferi sensu lato, even with those for which they are apparently not transmission competent (3, 5, 6, 9, 14, 15, 17). A possible explanation for this apparent paradox may be related to the fact that Borrelia genes are differentially expressed during the life cycle (4). While the gene expression of spirochetes residing in the tick's midgut resembles that observed in culture, major outer surface proteins of Borrelia, including possible complement receptors, appear to be down-regulated in the salivary glands of ticks and within the vertebrate host (4). Thus, it is possible that complement taken up by the tick during the blood meal selectively kills spirochetes in the tick's midgut (as seen in vitro), whereas spirochetes injected into the host by ticks whose salivary glands were infected prior to the uptake of blood may evade destruction. Studies to identify complement receptors on the spirochetes and to unveil the protective mechanisms of spirochetes against complement are under way.
Altogether, we conclude that complement plays a key role in the host-to-tick transmission of B. burgdorferi sensu lato and, as a consequence, in the global ecology of Lyme borreliosis.
| |
ACKNOWLEDGMENTS |
|---|
We thank M. M. Simon, Freiburg, Germany, and A. P. Van Dam, Amsterdam, The Netherlands, for kindly providing spirochetal strains; S. Butcher, Oxford, United Kingdom, for providing horse sera; S. Fletcher, Auchtermuchty, United Kingdom, for providing deer sera; and D. Strange, Oxford, United Kingdom, for providing squirrel sera.
| |
FOOTNOTES |
|---|
* Corresponding author. Mailing address: The Wellcome Trust Centre for the Epidemiology of Infectious Diseases, Department of Zoology, University of Oxford, South Parks Rd., Oxford OX1 3PS, United Kingdom. Phone: 44-1865-281630. Fax: 44-1865-281696. E-mail: kku{at}mail.nerc-oxford.ac.uk.
Editor: R. N. Moore
| |
REFERENCES |
|---|
|
|
|---|
| 1. | Breitner-Ruddock, S., R. Wurzner, J. Schulze, and V. Brade. 1997. Heterogeneity in the complement-dependent bacteriolysis within the species of Borrelia burgdorferi. Med. Microbiol. Immunol. 185:253-260[Medline]. |
| 2. | Craine, N. G., P. A. Nuttall, A. C. Marriott, and S. E. Randolph. 1997. Role of grey squirrels and pheasants in the transmission of Borrelia burgdorferi sensu lato, the Lyme disease spirochaete, in the UK. Folia Parasitol. 44:155-160. |
| 3. | Demaerschalck, I., A. Ben Massaoud, M. De Kesel, B. Hoyois, I. Lobet, P. Hoet, G. Bigaignon, A. Bollen, and E. Godfroid. 1995. Simultaneous presence of different Borrelia burgdorferi genospecies in biological fluids of Lyme disease patients. J. Clin. Microbiol. 33:602-608[Abstract]. |
| 4. | De Silva, A. M., and E. Fikrig. 1997. Borrelia burgdorferi genes selectively expressed in ticks and mammals. Parasitol. Today 13:267-270. [Medline] |
| 5. | Gorelova, B. N., E. I. Korenberg, Y. V. Kovalevskii, and S. V. Shcherbakov. 1995. Small mammals as reservoir hosts for Borrelia in Russia. Zentralbl. Bakteriol. 282:315-322[Medline]. |
| 6. | Humair, P. F. Personal communication. |
| 7. | Humair, P. F., O. Peter, R. Wallich, and L. Gern. 1995. Strain variation of Lyme disease spirochetes isolated from Ixodes ricinus ticks and rodents collected in two endemic areas in Switzerland. J. Med. Entomol. 32:433-438[Medline]. |
| 8. | Jaenson, T. G. T., and L. Talleklint. 1992. Incompetence of roe deer as reservoirs of the Lyme borreliosis spirochete. J. Med. Entomol. 29:813-817[Medline]. |
| 9. | Kimura, K., E. Isogai, H. Isogai, Y. Kamewaka, T. Nishikawa, N. Ishii, and N. Fujii. 1995. Detection of Lyme disease spirochetes in the skin of naturally infected wild Sika deer (Cervus nippon yesoensis) by PCR. Appl. Environ. Microbiol. 61:1641-1642[Abstract]. |
| 10. | Kirstein, F., S. Rijpkema, M. Molkenboer, and J. S. Gray. 1997. The distribution and prevalence of B. burgdorferi genomospecies in Ixodes ricinus ticks in Ireland. Eur. J. Epidemiol. 13:67-72[Medline]. |
| 11. |
Kurtenbach, K.,
A. Dizij,
H. M. Seitz,
G. Margos,
S. E. Moter,
M. D. Kramer,
R. Wallich,
U. E. Schaible, and M. M. Simon.
1994.
Differential immune responses to Borrelia burgdorferi in European wild rodent species influence spirochete transmission to Ixodes ricinus L. (Acari: Ixodidae).
Infect. Immun.
62:5344-5352 |
| 12. | Kurtenbach, K., A. Dizij, P. Voet, P. Hauser, and M. M. Simon. 1997. 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. Vaccine 15:1670-1674[Medline]. |
| 13. | Kurtenbach, K., D. Carey, A. Hoodless, P. A. Nuttall, and S. E. Randolph. Competence of pheasants as reservoirs for Lyme disease spirochetes. J. Med. Entomol., in press. |
| 14. | Kurtenbach, K., M. Peachey, S. G. T. Rijpkema, A. N. Hoodless, P. A. Nuttall, and S. E. Randolph. Differential transmission of the genospecies of Borrelia burgdorferi sensu lato by game birds and small rodents in England. Appl. Environ. Microbiol., in press. |
| 15. | Nakao, M., K. Miyamoto, and M. Fukunaga. 1994. Borrelia japonica in nature: genotypic identification of spirochetes isolated from Japanese small mammals. Microbiol. Immunol. 38:805-808[Medline]. |
| 16. | Nakao, M., K. Miyamoto, and M. Fukunaga. 1994. Lyme disease spirochetes in Japan: enzootic transmission cycles in birds, rodents, and Ixodes persulcatus ticks. J. Infect. Dis. 170:878-882[Medline]. |
| 17. | Nakao, M., and K. Miyamoto. 1995. Mixed infection of different Borrelia species among Apodemus speciosus mice in Hokkaido, Japan. J. Clin. Microbiol. 33:490-492[Abstract]. |
| 18. | Ogden, N. H., P. A. Nuttall, and S. E. Randolph. Natural Lyme disease cycles maintained via sheep by co-feeding ticks. Parasitology, in press. |
| 19. | Olsen, B., T. G. T. Jaenson, L. Noppa, J. Bunikis, and S. A. Bergström. 1993. A Lyme borreliosis cycle in seabirds and Ixodes uriae ticks. Nature (London) 362:340-342[Medline]. |
| 20. | Olsen, B., T. G. T. Jaenson, and S. A. Bergström. 1995. Prevalence of Borrelia burgdorferi sensu lato-infected ticks on migrating birds. Appl. Environ. Microbiol. 61:3082-3087[Abstract]. |
| 21. | Padilla, M. L., S. M. Callister, R. F. Schell, G. L. Bryant, D. A. Jobe, S. D. Lovrich, B. K. DuChateau, and J. R. Jensen. 1996. Characterization of the protective borreliacidal antibody response in humans and hamsters after vaccination with a Borrelia burgdorferi outer surface protein A vaccine. J. Infect. Dis. 174:739-746[Medline]. |
| 22. |
Postic, D.,
M. Assous,
P. A. D. Grimont, and G. Baranton.
1994.
Diversity of Borrelia burgdorferi sensu lato evidenced by restriction fragment length polymorphism of rrf(5S)-rrl(23S) intergenic spacer amplicons.
Int. J. Syst. Bacteriol.
44:743-752 |
| 23. | Rijpkema, S. G. T., M. J. C. H. Molkenboer, L. M. Schouls, F. Jongejan, and J. F. P. Schellekens. 1995. Simultaneous detection and genotyping of three genomic groups of Borrelia burgdorferi sensu lato in Dutch Ixodes ricinus ticks by characterization of the amplified intergenic spacer region between 5S and 23S rRNA genes. J. Clin. Microbiol. 33:3091-3095[Abstract]. |
| 24. | Rijpkema, S. G. T., and H. Bruinink. 1996. Detection of Borrelia burgdorferi sensu lato by PCR in questing Ixodes ricinus larvae from the Dutch North Sea island of Ameland. Exp. Appl. Acarol. 20:381-385[Medline]. |
| 25. | Rijpkema, S. G. T., R. G. Herbes, N. Verbeek-De Kruif, and J. F. P. Schellekens. 1996. Detection of four Borrelia burgdorferi sensu lato in Ixodes ricinus ticks collected from Dutch roe deer (Capreolus capreolus). Epidemiol. Infect. 117:563-566[Medline]. |
| 26. | Talleklint, L., and T. G. T. Jaenson. 1994. Transmission of Borrelia burgdorferi s.l. from mammal reservoirs to the primary vector of Lyme borreliosis, Ixodes ricinus (Acari: Ixodidae), in Sweden. J. Med. Entomol. 31:880-886[Medline]. |
| 27. | Telford, S. R., III, T. N. Mather, S. I. Moore, M. L. Wilson, and A. Spielman. 1988. Incompetence of deer as reservoirs of the Lyme disease spirochete. Am. J. Trop. Med. Hyg. 39:105-109. |
| 28. | Van Dam, A. P., H. Kuiper, K. Vos, A. Widjojokusumo, L. Spanjaard, B. M. De Jongh, A. C. P. Ramselaar, M. D. Kramer, and J. Dankert. 1993. Different genospecies of Borrelia burgdorferi are associated with distinct clinical manifestations in Lyme borreliosis. Clin. Infect. Dis. 17:708-717[Medline]. |
| 29. | Van Dam, A. P., A. Oei, R. Jaspars, C. Fijen, B. Wilske, L. Spanjaard, and J. Dankert. 1997. Complement-mediated serum sensitivity among spirochetes that cause Lyme disease. Infect. Immun. 65:1228-1236[Abstract]. |
| 30. |
Whaley, K., and J. North.
1997.
Haemolytic assays for whole complement activity and individual components, p. 19-48. In
A. W. Dodds, and R. B. Sim (ed.), Complement a practical approach.
IRL Press, New York, N.Y.
|
| 31. | Will, G., S. Jauris-Heipke, E. Schwab, U. Busch, D. Rössler, E. Soutschek, B. Wilske, and V. Preac-Mursic. 1995. Sequence analysis of ospA genes shows homogeneity within Borrelia burgdorferi sensu stricto and Borrelia afzelii strains but reveals major subgroups within Borrelia garinii species. Med. Microbiol. Immunol. 184:73-80[Medline]. |
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»