Here are more references regarding the possibility of transovarial transmission -- from oldest to newest, with a few that are undated:
http://www.tickencounter.org/tick_notes ... _miyamotoi
http://www.vetmed.wisc.edu/pbs/zoonoses ... trans.html
But there are certain pathogens that CAN be passed on from an infected female tick through the egg stage and into the next generation of ticks, a process called transovarial (t/o) transmission. Pathogens capable of t/o transmission infect at least a portion of the new larval cohort, and conceptually, can be transmitted by the larvae when they bite.
Borrelia miyamotoi is a t/o transmitted bacterium in ticks. First reported in 1995 (1) infecting Ixodes persulcatus ticks in Japan, strains of this microbe also have been recovered in other Ixodes tick species, including Ixodes ricinus ticks in Europe as well as deer ticks and western blacklegged ticks in the United States.
Previously, 1.9 - 2.5% of host-seeking nymphal deer ticks collected in RI, CT, NY & NJ were shown to be infected with B. miyamotoi (2). In a preliminary study, TERC researchers recently found that 9% of egg-laying female deer ticks collected in Rhode Island passed B. miyamotoi infection to their offspring (larvae), and this study and other estimates suggest that 6 - 73% of larvae hatching from eggs laid by B. miyamotoi-infected females may be infected. It's still unknown how efficient these t/o infected larvae are in transmitting infection to humans.
In fact, until recently there was no evidence that Borrelia miyamotoi caused human infection. However, a study reported in the journal Emerging Infectious Disease in 2011 (3) reported on 46 human cases of influenza-like illness with high fever, all associated with Borrelia miyamotoi infection in Yekaterinburg City, Russia.
The study was clear that these cases WERE NOT Lyme disease. In some of the cases, a relapsing fever syndrome was observed. Other strains of Borrelia in the U.S. and elsewhere are known to cause relapsing fever.
The geographic extent of relapsing fever disease caused by Borrelia miyamotoi remains to be determined. But given the comparable tick infection rates between the Yekaterinburg region in Russia and other places where this pathogen has been detected, including here in the U.S., human infection likely does occurs outside of Russia.
Tick transmission of Borrelia burgdorferi
B. burgdorferi is transmitted by the Ixodes ("deer tick") family of "3 host" ticks. These ticks require 2 years to complete their life cycle and must feed on 3 independent hosts during this cycle. (Click here for a photo of the larvae, nymph and adult Ixodes scapularis ticks)
There is minimal transovarial transmission of B. burgdorferi in ticks, so each new generation of ticks must be infected de novo by feeding on an infected host. The organism can, however, be transmitted transstadially from larvae to nymph to adult.
In general, the tick larvae first become infected by feeding on rodents that are competent hosts for B. burgdorferi (i.e., these rodent hosts replicate B. burgdorferi to a sufficient level to be infectious for subsequently feeding ticks).
Robins have also been shown to be competent hosts for B. burgdorferi.
In the southeastern and western U.S., reptiles may also serve as competent hosts, although, conversely, some lizards contain a borreliacidal substance in their blood that eliminates Borrelia from feeding ticks.
The tick nymphs and especially adults obtain their blood meals by feeding on larger mammals. Deer are the preferred enzootic feeding hosts- dogs, horses, cows, people etc. are accidental victims of a hungry tick!
Deer are not competent hosts for B. burgdorferi - their role is to maintain the ticks, not the Borrelia.
Nymphs are the life stage most commonly involved in transmitting B. burgdorferi to dogs and humans.
Zentralbl Bakteriol Mikrobiol Hyg A. 1986 Dec;263(1-2):29-33.
Borrelia transfer by ticks during their life cycle. Studies on laboratory animals.
Stanek G, Burger I, Hirschl A, Wewalka G, Radda A.
Ticks of the species Ixodes ricinus were cultured in the laboratory. Yellow silver rabbits, gerbils and white mice served as blood hosts. Borrelia burgdorferi could be detected by means of an IFA test in homogenates of female ticks, their eggs as well as the respective larval and nymphal ticks. Blood infection of splenectomized gerbils and ordinary white mice or of ordinary white mice alone has been demonstrated after feeding of larval or nymphal ticks on them, respectively. Spirochetemia started 5 to 8 days after feeding and lasted for ca 3 weeks. Two distinct peaks in the cell count of spirochetal organisms per ml blood plasma could be observed on days 11-13 (5 X 10(5) to 2 X 10(6) cells/ml) and 17-19 (10(5) cells/ml), regardless whether splenectomized gerbils or white mice were used. The results display that B. burgdorferi is vertically from the female ticks to their eggs and transstadially transmitted. The transmission-rate from larval to nymphal ticks is 100%. These findings show the tick itself as a main reservoir of B. burgdorferi. The established mouse-model appears to be a useful tool to detect Borrelia carrying ticks.
[PubMed - indexed for MEDLINE]
Exp Appl Acarol. 1993 Aug;17(8):581-6.
Ability of transovarially and subsequent transstadially infected Ixodes hexagonus ticks to maintain and transmit Borrelia burgdorferi in the laboratory.
Toutoungi LN, Gern L.
Institut de Zoologie, University of Neuchâtel, Chantemerle 22, CH-2000 Neuchâtel, Switzerland.
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.
[PubMed - indexed for MEDLINE]
J Med Entomol. 1993 Jan;30(1):80-6.
Efficiency of transovarial transmission of the Lyme disease spirochete, Borrelia burgdorferi, in the western blacklegged tick, Ixodes pacificus (Acari: Ixodidae).
Schoeler GB, Lane RS.
Department of Entomological Sciences, University of California, Berkeley 94720.
The efficiency of transovarial transmission of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner was evaluated in Ixodes pacificus Cooley & Kohls collected from two areas of northern California where Lyme disease is endemic. In total, 132 (8.8%) of 1,499 replete females examined by direct immunofluorescence were demonstrated to be infected with B. burgdorferi. Larvae or eggs from 119 of these females were examined for the presence of spirochetes by direct immunofluorescence, placing them in culture, or both; none was found to contain B. burgdorferi. The fecundity of 20 midgut-infected (mean = 874.2) and 20 uninfected (mean = 1,048.3) I. pacificus females did not differ statistically. Likewise, the fertility of infected (mean = 87.0%) and uninfected (mean = 89.9%) females and the mean engorged weights of both groups (infected, 120.8 mg versus uninfected, 132.7 mg), were comparable. The fecundity, fertility, and mean weights of six replete females having ovarian infections, six females having midgut-restricted infections, and six uninfected females were also similar. We conclude that transovarial transmission is not efficient for maintaining B. burgdorferi in populations of I. pacificus, a known vector of that pathogen. Infection with the spirochete does not appear to affect either feeding or reproductive success adversely in females of this tick.
[PubMed - indexed for MEDLINE]
Exp Appl Acarol. 1994 Sep;18(9):531-42.
Infection rates of Borrelia burgdorferi in different instars of Ixodes ricinus ticks from the Dutch North Sea Island of Ameland.
Rijpkema S, Nieuwenhuijs J, Franssen FF, Jongejan F.
Laboratory of Bacteriology and Antimicrobial Agents, National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands.
Between 1988 and 1993, a total of 7173 I. ricinus ticks, predominantly, were collected from the vegetation on the Dutch North Sea Island of Ameland. A proportion of the ticks (n = 547) was screened for the presence of Borrelia by immunofluorescence. Infection rates of Borrelia varied, in nymphs (n = 347) from 13% to 46% and in adults, (n = 122) from 20% to 43%. The infection rate in larvae (n = 84) collected in 1993 was 21%, showing that transovarial transmission of B. burgdorferi occurs in the I. ricinus population on Ameland. Two tick-naive sheep seroconverted for B. burgdorferi after field-collected adult or nymphal I. ricinus were allowed to feed on them. Larval progeny (n = 168) of 15 female adult ticks fed on one of these sheep were free from B. burgdorferi. B. burgdorferi was isolated in culture from field-collected adult ticks. Serotyping using monoclonal antibodies against outer surface proteins A and C indicated that both isolated belonged to genospecies B. garinii, and this was confirmed by DraI restriction analysis of the variable DNA sequence between the 5S and 23S rRNA genes.
[PubMed - indexed for MEDLINE]
Epidemiol Infect. 1996 Dec;117(3):563-6.
Detection of four species of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks collected from roe deer (Capreolus capreolus) in The Netherlands.
Rijpkema SG, Herbes RG, Verbeek-De Kruif N, Schellekens JF.
Research Laboratory for Infectious Diseases, National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
Roe deer (Capreolus capreolus) were investigated for their value as sentinel animals for Lyme borreliosis in the Netherlands. Serum was obtained from 114 roe deer, and 513 Ixodes ricinus, predominantly females (72%), were obtained from 47 animals (41%). The polymerase chain reaction was used to detect DNA of Borrelia burgdorferi sensu lato in a total of 190 ticks, comprising 106 engorged ticks and 84 non-engorged ticks. Borrelia DNA was detected in 24 engorged ticks (23%) and 26 non-engorged ticks (31%). This difference was not significant (P = 0.25). Four species of B. burgdorferi sensu lato were identified in the ticks. B. burgdorferi sensu stricto, Borrelia garinii, Borrelia afzelii and group VS116. B. afzelii was most commonly found and present in 13 mixed infections, and in 28 single infections. Fifteen sera (13%) contained antibodies to Borrelia spp. Ticks are more appropriate sentinel animals for Lyme borreliosis than roe deer, an important host for I. ricinus. Although the viability of borrelia spirochaetes in engorged ticks collected from roe deer was not assessed, a bloodmeal taken from roe deer did not eliminate borrelia spirochaetes from the tick. The relevance of this finding for transovarial transmission of borrelia spirochaetes in ticks is discussed.
[PubMed - indexed for MEDLINE]
Free PMC Article
The full article is here (in the form of a scanned copy of the original print version):
http://www.afpmb.org/sites/default/file ... 169235.pdf
Experimental & Applied Acarology, 22 (1998) 249-258
The ecology of ticks transmitting Lyme borreliosis
Department of Environmental Resource Management, University College Dublin, Belfield 4,
Dublin, Republic of Ireland
(Received November 1996; accepted 6 February 1998)
The main vectors of Borrelia burgdorferi sensu lato, the cause of Lyme borreliosis, are ixodid
ticks of the lxodes persulcatus species complex. These ticks, which occur throughout the northern
temperate zone, have very similar life cycles and ecological requirements. All are three-host ticks,
with the immature stages mainly parasitizing small to medium-sized mammals and birds and the
adult females parasitizing large mammals such as deer, cattle, sheep and hares. The host-seeking
stages show a distinct seasonality, which is regulated by diapause mechanisms and there appear to be major differences in this respect between the Old World and New World species. Most
cases of human borreliosis are transmitted in the summer by the nymphal stages, with the
exception of the Eurasian species, I. persulcatus, in which the adult females are mainly
responsible. The ticks acquire the spirochaetes from a wide variety of mammals and birds but
large mammals do not seem to be infective, so that ticks that feed almost exclusively on large
mammals, for example in some agricultural habitats, are rarely infected. The greatest tick
infection prevalences occur in deciduous woodland harbouring a diverse mix of host species and
the diversity of the different genospecies of B. burgdorferi s.1. is also greatest in such habitats.
There is evidence that these genospecies have different host predilections but, apart from the fact
that I. persulcatus does not seem to be infected by B. burgdorferi sensu stricto, they do not seem
to be adapted to different tick strains or species.
Exp Appl Acarol 22:249-258 (C) 1998 Chapman & Hall Ltd
THE TRANSMISSION OF LYME BORRELIOSIS
Much remains to be learned about the details of Borrelia burgdorferi transmission,
but some facts are now well-established. In most unfed ticks, the spirochaetes
inhabit the midgut and during feeding they penetrate the midgut wall and translocate
to the salivary glands via the haemolymph. They then pass into the feeding
lesion with the saliva. The migration of spirochaetes from the gut to the salivary
glands during feeding means that most infections do not take place for at least 2
days after attachment; however, in a proportion of unfed ticks the spirochaetes are
already present in the salivary glands and transmission can take place much sooner
(Korenberg et al., 1994; Leuba-Garcia et al., 1994). At one time regurgitation of
the gut contents into the feeding lesion was considered to be possible and could
explain early transmission, but so far no convincing evidence has appeared to
support this hypothesis. Trans-stadial transmission (stage to stage) rather than
transovarial transmission (from an infected female to her eggs) normally takes place
so that the infection is usually acquired from a reservoir host by the larvae or
nymphs, and transmitted by the nymphs or adults. Transovarial transmission is
uncommon and the larval infection rates are usually less than 1% so that the larvae
are not considered to be a significant source of infection for humans. However, in
an attempt to explain the fact that in Europe rodents seem to become infected
despite feeding few infecting nymphs, it has been suggested that transovarial
transmission may have a considerable role in maintaining the circulation of the
spirochaete in nature (de Boer et al., 1993). So far no consistent experimental
transmission of spirochaetes by the larvae has been shown and the precise role of
rodents in the circulation of spirochaetes between the hosts and ticks remains to be
Appl Environ Microbiol. 1998 August; 64(8): 3089–3091.
Failure of Ixodes Ticks To Inherit Borrelia afzelii Infection
Franz-Rainer Matuschka,1,2 Thomas W. Schinkel,1 Birte Klug,1 Andrew Spielman,2 and Dania Richter1,2,*
Institut für Pathologie, Charité, Medizinische Fakultät der Humboldt-Universität zu Berlin, 12249 Berlin, Germany,1 and Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts 021152
*Corresponding author. Mailing address: Department of Immunology and Infectious Diseases, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115.
To define conditions promoting inherited infection by Lyme disease spirochetes in Ixodes ticks, we variously infected ticks with Borrelia afzelii and examined their progenies by dark-field microscopy, immunofluorescence, PCR, and serial passage. No episode of inherited infection was evident, regardless of instar or gender infected or frequency of exposure. We suggest that these spirochetes rarely, if ever, are inherited by vector ticks.
FOLIA PARASITOLOGICA 51: 67–71, 2004
Studies on the transovarial transmission of Borrelia burgdorferi sensu lato in the taiga tick Ixodes persulcatus
Valentina V. Nefedova, Edward I. Korenberg, Nataliya B. Gorelova and Yury V. Kovalevskii
Gamaleya Research Institute for Epidemiology and Microbiology, Russian Academy of Medical Sciences, 18 Gamaleya Street, 123098 Moscow, Russia
Key words: Borrelia burgdorferi, Ixodes persulcatus, ticks, transovarial transmission
Abstract. The possibility of vertical transmission of Borrelia burgdorferi sensu lato in Ixodes persulcatus Schulze, 1930 ticks was studied in the progeny of 20 females collected from the vegetation in an active focus of ixodid tick-borne borrelioses (ITBB) located in the Perm oblast, Russia, where Borrelia garinii and B. afzelii are circulating. The presence of Borrelia DNA was detected by the PCR method after feeding and egg laying in 16 engorged females (80.0%), as well as in 36.5 ± 7.2% samples containing 20 eggs each and in 21.4 ± 4.2% samples containing 10 eggs each. The respective rates of individual egg infection were 0.4−8.0% and 0.5−23.0%. PCR analysis of 370 eggs (one egg per sample) and 781 unfed larvae hatched from the same egg masses (1, 10, 20, 40, and 50 larvae per sample) failed to reveal the presence of Borrelia DNA. Negative results were also obtained in experiments on inoculating the BSK II medium with the egg and larval materials. Microscopic analysis of 1,683 smear preparations of eggs and 1,416 preparations of unfed daughter larvae revealed spirochete-like cells in 7 (0.4 ± 0.3%) and 13 (0.9 ± 0.5%) preparations, respectively; typical Borrelia cells were found in seven preparations of larvae (0.5 ± 0.4%). Only 1 out of 16 infected females transmitted Borrelia vertically, through the eggs to the larval progeny. The infection rate in this progeny was about 7%, and the prevalence of Borrelia in individual larvae was 0.4−0.8 cells per 100 microscopic fields. These data do not allow the conclusion that transovarial transmission of B. burgdorferi sensu lato in the I. persulcatus tick is an established fact. However, they show that, even if such transmission is possible, its probability is very low.
http://wwwnc.cdc.gov/eid/article/8/2/01 ... rticle.htm
Transmission of the Lyme Disease Spirochete
Transmission of the Lyme Disease Spirochete
By Louis A. Magnarelli
Department of Entomology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P.O. Box 1106
New Haven, CT 06504-1106
The rise in deer populations over several decades in and near forests is correlated with substantial increases in blacklegged ticks and corresponding amplification of the disease organism in nature. Although deer are important hosts for adult blacklegged ticks, they do not serve to infect ticks. White-footed mice are considered the chief reservoirs for the Lyme disease agent. Larval and nymphal blacklegged ticks acquire the pathogen when they feed on these rodents and possibly other hosts, such as chipmunks and some birds. The disease organism can then be passed from larvae to nymphs to adults during the developmental process. There is occasional passage of the disease agent from infected females to larvae (via the eggs), but this form of pathogen transmission is not considered to be epidemiologically significant.1
1. Magnarelli, L.A., J. F. Anderson, and D. Fish. 1987. Transovarial transmission of Borrelia burgdorferi in Ixodes dammini (Acari: Ixodidae). Journal of Infectious Diseases 156:234-236.
2. Piesman, J., T. N. Mather, R. J. Sinsky, et al. 1987. Duration of tick attachment and Borrelia burgdorferi transmission. Journal of Clinical Microbiology 25:557-558.
3. des Vignes, F., J. Piesman, R. Heffernan, et al. 2001. Effect of tick removal on transmission of Borrelia burgdorferi and Ehrlichia phagocytophila by Ixodes scapularis nymphs. Journal of Infectious Diseases 183:773-778.
4. Piesman, J. and M. C. Dolan. 2002. Protection against Lyme disease spirochete transmission provided by prompt removal of nymphal Ixodes scapularis (Acari: Ixodidae). Journal of Medical Entomology 39:509-512.
Vector Interactions and Molecular Adaptations of Lyme Disease and Relapsing Fever Spirochetes Associated with Transmission by Ticks
Tom G. Schwan* and Joseph Piesman†
Author affiliations: *National Institutes of Health, Hamilton, Montana, USA; †Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
Pathogenic spirochetes in the genus Borrelia are transmitted primarily by two families of ticks. The Lyme disease spirochete, Borrelia burgdorferi, is transmitted by the slow-feeding ixodid tick Ixodes scapularis, whereas the relapsing fever spirochete, B. hermsii, is transmitted by Ornithodoros hermsi, a fast-feeding argasid tick. Lyme disease spirochetes are generally restricted to the midgut in unfed I. scapularis. When nymphal ticks feed, the bacteria pass through the hemocoel to the salivary glands and are transmitted to a new host in the saliva after 2 days. Relapsing fever spirochetes infect the midgut in unfed O. hermsi but persist in other sites including the salivary glands. Thus, relapsing fever spirochetes are efficiently transmitted in saliva by these fast-feeding ticks within minutes of their attachment to a mammalian host. We describe how B. burgdorferi and B. hermsii change their outer surface during their alternating infections in ticks and mammals, which in turn suggests biological functions for a few surface-exposed lipoproteins.
The principal tick vectors of Lyme disease spirochetes in North America are I. scapularis and I. pacificus; the developmental stage of the former species that transmits most human infections is the nymph. Although transmission by adult I. scapularis or transovarially infected larvae remains possible, our review focuses on tick-spirochete interactions within nymphal I. scapularis. Larval ticks ingest spirochetes from infected reservoir hosts, molt, and emerge as nymphs. When spirochetes are ingested by larvae, they rapidly multiply in the replete tick until the nymphal molt, when a precipitous drop in spirochete numbers occurs (10,11). Thus, at the time questing nymphs are likely to contact their potential victims, spirochete numbers are at their lowest and generally restricted to the lumen of the midgut. When nymphal feeding begins, a pronounced multiplication of spirochetes takes place in the tick. Nymphal I. scapularis take approximately 3 to 4 days to complete feeding. Spirochete numbers are reported to increase >300- fold during this feeding period, increasing from a mean of 496 spirochetes in unfed nymphs to 166,575 at 72 hours after attachment (12). Along with this rapid multiplication, other changes are taking place in the spirochete population that may lay the groundwork for eventual transmission to the host.
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Vector Borne Zoonotic Dis. 2012 Jan;12(1):21-7. Epub 2011 Sep 16.
Absence of Lyme disease spirochetes in larval Ixodes ricinus ticks.
Richter D, Debski A, Hubalek Z, Matuschka FR.
Abt. Parasitologie, Institut für Pathologie, Charité Universitätsmedizin Berlin, Berlin, Germany
To determine which kind of spirochete infects larval Ixodes ricinus, we examined questing larvae and larvae derived from engorged females for the presence of particular spirochetal DNA that permitted species differentiation. Borrelia miyamotoi was the sole spirochete detected in larval ticks sampled while questing on vegetation. Questing nymphal and adult ticks were infected mainly by Borrelia afzelii, whereas larval ticks resulting from engorged females of the same population were solely infected by B. miyamotoi. Since larvae acquire Lyme disease spirochetes within a few hours of attachment to an infected rodent, questing larvae in nature may have acquired Lyme disease spirochetes from an interrupted host contact. Even if transovarial transmission of Lyme disease spirochetes may occasionally occur, it seems to be an exceedingly rare event. No undisputable proof exists for vertical transmission of Lyme disease spirochetes, whereas B. miyamotoi appears to be readily passed between generations of vector ticks.
[PubMed - indexed for MEDLINE]
Nat Rev Microbiol. 2012 Jan 9;10(2):87-99. doi: 10.1038/nrmicro2714.
Of ticks, mice and men: understanding the dual-host lifestyle of Lyme disease spirochaetes.
Radolf JD, Caimano MJ, Stevenson B, Hu LT.
Department of Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
In little more than 30 years, Lyme disease, which is caused by the spirochaete Borrelia burgdorferi, has risen from relative obscurity to become a global public health problem and a prototype of an emerging infection. During this period, there has been an extraordinary accumulation of knowledge on the phylogenetic diversity, molecular biology, genetics and host interactions of B. burgdorferi. In this Review, we integrate this large body of information into a cohesive picture of the molecular and cellular events that transpire as Lyme disease spirochaetes transit between their arthropod and vertebrate hosts during the enzootic cycle.
[PubMed - indexed for MEDLINE]
Free PMC Article
The full article is here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3313462/
http://www.ncbi.nlm.nih.gov/pmc/article ... figure/F1/
The enzootic cycle of Borrelia burgdorferi. Ixodes spp. ticks undergo a three-stage life cycle — larva, nymph and adult — with one blood meal per stage. Although some Borrelia spp. that cause relapsing fever can be passed from adult to egg (transovarial transmission), this does not occur with B. burgdorferi, so each generation of tick must acquire a B. burgdorferi infection anew. Larval ticks feed on many different animals, including Peromyscus spp. mice, squirrels and birds. B. burgdorferi infection is acquired by feeding on an infected reservoir animal, and the bacterium is retained during the subsequent stages (that is, trans-stadially) after each blood meal and moult7,10. Nymphs feed on a similar range of hosts to larvae; transmission of spirochaetes to a competent reservoir host by a feeding nymph perpetuates the enzootic cycle for the next generation of larval ticks. Although small mammals are usually thought of as the primary reservoirs for Lyme disease spirochaetes, studies have called attention to the importance of migratory birds as disseminators of spirochaetes over large distances7,10. Adult ticks are not generally important for maintenance of B. burgdorferi in the wild, as they feed predominantly on larger animals such as deer, which are incompetent hosts for B. burgdorferi7. However, deer are important for maintenance of the tick population because adult ticks mate on them. Although all three stages of Ixodes scapularis can feed on humans, nymphs are responsible for the vast majority of spirochaete transmission to humans. It is unknown whether infected humans can transmit spirochaetes to feeding larvae, and humans are generally considered dead-end hosts and not part of the enzootic cycle. Dogs are probably incidental hosts and not part of the enzootic cycle.