Vector interactions and molecular adaptations of Lyme disease and relapsing fever spirochetes associated with transmission by ticks. (Perspectives).
Pathogenic spirochetes in the genus Borrelia are transmitted primarily by two families of ticks. The Lyme disease Lyme disease, a nonfatal bacterial infection that causes symptoms ranging from fever and headache to a painful swelling of the joints. The first American case of Lyme's characteristic rash was documented in 1970 and the disease was first identified in a cluster at spirochete spirochete
Any of an order (Spirochaetales) of spiral-shaped bacteria. Some are serious pathogens for humans, causing such diseases as syphilis, yaws, and relapsing fever. Spirochetes are gram-negative (see gram stain) and motile. , Borrelia burgdorferi Borrelia burg·dor·fe·ri
A spirochete causing Lyme disease in humans.
Borrelia burgdorferi The spirochete agent of Lyme disease, which contains several outer membrane proteins and a highly immunogenic flagellar , is transmitted by the slow-feeding ixodid tick Ixodes scapularis Ixodes scapularis Deer tick A tick with a 2-yr life cycle, and 3 feeding seasons; the cycle begins in spring with soil deposition of fertilized eggs; by summer, larvae emerge and imbibe a blood meal from small vertebrates–eg, white-footed mouse– , whereas the relapsing fever relapsing fever
Infectious disease with recurring fever, caused by several spirochetes of the genus Borrelia, transmitted by lice, ticks, and bedbugs. Onset is sudden, with high fever, which breaks within a week with profuse sweating. Symptoms return about a week later. spirochete, B. hermsii, is transmitted by Ornithodoros hermsi, a fast-feeding argasid tick argasid tick
tick belonging to the family Argasidae. . Lyme disease spirochetes are generally restricted to the midgut midgut /mid·gut/ (mid´gut) the region of the embryonic digestive tube into which the yolk sac opens and which gives rise to most of the intestines; ahead of it is the foregut and caudal to it is the hindgut. in unfed I. scapularis. When nymphal nymph
1. Greek & Roman Mythology Any of numerous minor deities represented as beautiful maidens inhabiting and sometimes personifying features of nature such as trees, waters, and mountains.
2. ticks feed, the bacteria pass through the hemocoel he·mo·coel
A cavity or series of spaces between the organs of most arthropods and mollusks through which the blood circulates. to the salivary glands salivary glands (săl`əvâr'ē), in humans, three pairs of glands that secrete the alkaline digestive fluid, saliva, into the mouth. 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 Lipoproteins
The packages in which cholesterol and triglycerides travel throughout the body.
Mentioned in: Lipoproteins Test
The molecular adaptations required by pathogenic spirochetes for efficient transmission by obligate obligate /ob·li·gate/ (ob´li-gat) pertaining to or characterized by the ability to survive only in a particular environment or to assume only a particular role, as an obligate anaerobe. , blood-feeding ticks are largely unknown. In the new era of genomics, the complete DNA sequence DNA sequence Genetics The precise order of bases–A,T,G,C–in a segment of DNA, gene, chromosome, or an entire genome. See Base pair, Base sequence analysis, Chromosome, Gene, Genome. of two spirochetes, Borrelia burgdorferi and Treponema pallidum Treponema pal·li·dum
A spirochete that causes syphilis in humans.
Treponema pallidum Infectious disease The spirochete that causes syphilis Epidemiology 9000 cases/yrs–US, primarily in the SE US. , have been determined (1, 2). As additional genome sequences become available for other pathogenic and free-living spirochetes, comparisons of their genomes may elucidate genes that are unique to those species of spirochetes associated with ticks. This information, along with an increased understanding of the molecular mechanisms used by tick-borne spirochetes to adapt for transmission by their tick vectors, may lead to unique disease prevention strategies.
The genus Borrelia currently contains 37 species of spirochetes, many of which cause diseases in humans and domestic animals (Table) (3). Except for B. recurrentis (which causes louse-borne relapsing fever and is transmitted by the human body louse body louse
A parasitic louse that infests the body and clothes of humans. ), all known species are transmitted by ticks (4). Two groups of spirochetes stand out among these tick-borne species because of their prevalence as human pathogens: Lyme disease spirochetes, transmitted by the relatively slow-feeding ixodid (hard) ticks of the genus Ixodes, and relapsing fever spirochetes, transmitted by the fast-feeding argasid (soft) ticks of the genus Ornithodoros (Figure 1). Major observations in recent years have increased our understanding of how one species in each group adapts while infecting ticks. B. burgdorferi, a causative agent of Lyme disease, and B. hermsii, a causative agent of tick-borne relapsing fever, have received the most attention. We describe how these two species of Borrelia Borrelia
A genus of spirochetes that have a unique genome composed of a linear chromosome and numerous linear and circular plasmids. Borreliae are motile, helical organisms with 4–30 uneven, irregular coils, and are 5–25 micrometers long and 0. 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 dynamics of infection of these two bacteria in strikingly different types of ticks provide examples of possible adaptations for their transmission.
[FIGURE 1 OMITTED]
B. burgdorferi-Tick Interactions
Detailed studies of B. burgdorferi were initiated in 1982 when Burgdorfer and coworkers reported these bacteria in adult Ixodes scapularis ticks collected from vegetation on Shelter Island, New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of (5). These researchers observed that spirochetes were commonly present in the midgut of infected ticks and occasionally seen in the hindgut hindgut /hind·gut/ (-gut) the embryonic structure from which the caudal intestine, chiefly the colon, is formed.
1. The large intestine, rectum, and anal canal.
2. and rectal ampule ampule /am·pule/ (am´pul) a small glass or plastic container capable of being sealed so as to preserve its contents in a sterile condition; used principally for sterile parenteral solutions. . No spirochetes were observed in other tissues, including the salivary glands. During this initial period of study of Lyme disease spirochetes, how vector ticks actually transmitted this new pathogen was the subject of much discussion. Because spirochetes were reported to be restricted to the digestive tract digestive tract
See alimentary canal.
The organs that perform digestion, or changing of food into a form that can be absorbed by the body. of ticks, some investigators speculated that transmission occurred by tick regurgitation regurgitation /re·gur·gi·ta·tion/ (re-ger?ji-ta´shun)
1. flow in the opposite direction from normal.
2. vomiting. or fecal contamination (6). These inefficient routes of transmission became a less likely explanation after spirochetes were described in the hemolymph hemolymph /he·mo·lymph/ (he´mo-limf?)
1. blood and lymph.
2. the bloodlike fluid of those invertebrates having open blood-vascular systems.
n. (7) and salivary glands of feeding ticks (8). The hypothesis that Lyme disease spirochetes were transmitted via the salivary gland salivary gland
Any of the organs that secrete saliva. Three pairs of major glands secrete saliva into the mouth through distinct ducts: the parotid glands (the largest), between the ear and the back of the lower jaw; the submaxillary glands, along the side of the lower jaw; route was confirmed when spirochetes were actually identified in tick saliva (9).
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 nymph, in Greek mythology
nymph (nĭmf), in Greek mythology, female divinity associated with various natural objects. It is uncertain whether they were immortal or merely long-lived. There was an infinite variety of nymphs. . Although transmission by adult I. scapularis or transovarially infected larvae Larvae, in Roman religion
Larvae: see lemures. remains possible, our review focuses on tick-spirochete interactions within nymphal I. scapularis. Larval larval
1. pertaining to larvae.
see cutaneous and visceral larva migrans. ticks ingest in·gest
tr.v. in·gest·ed, in·gest·ing, in·gests
1. To take into the body by the mouth for digestion or absorption. See Synonyms at eat.
2. spirochetes from infected reservoir hosts, molt, and emerge as nymphs. When spirochetes are ingested in·gest
tr.v. in·gest·ed, in·gest·ing, in·gests
1. To take into the body by the mouth for digestion or absorption. See Synonyms at eat.
2. 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.
Spirochete Surface Proteins
Virtually all spirochetes in the midgut of an unfed nymph express outer surface protein (Osp) A. This protein is also the predominant surface antigen expressed by the spirochetes in vitro in vitro /in vi·tro/ (in ve´tro) [L.] within a glass; observable in a test tube; in an artificial environment.
In an artificial environment outside a living organism. . As the nymphal ticks start to feed and the spirochetes in the midgut begin to multiply rapidly, most spirochetes cease expressing OspA on their surface (13,14). Simultaneous with the disappearance of OspA, the spirochete population in the midgut begins to express a different Osp, OspC (15). Upregulation of OspC begins during the first day of feeding and peaks 48 hours after attachment (14). After this time point, the proportion of spirochetes in the midgut expressing OspC decreases rapidly. Therefore, the repression of OspA synthesis and upregulation of OspC correlate with the exit of spirochetes from the midgut, dissemination through the hemolymph, and passage through the salivary glands of the feeding tick. Several researchers have hypothesized that OspA binds spirochetes to the tick midgut (14,16,17). By downregulating OspA, the spirochetes might free themselves to migrate through the midgut epithelium and out of the midgut. Recently, purified OspA of B. burgdorferi was shown to bind to to contract; as, to bind one's self to a wife s>.
See also: Bind suspensions of tick midgut cells. The binding domains apparently reside in both the central and carboxy-terminus of the OspA protein; OspA also binds to itself (16). Thus, a picture emerges of aggregates of OspA-positive spirochetes bound to the tick midgut. Also, B. burgdorferi and B. afzelii expressing OspA were shown recently to adhere to tick-cell cultures more readily than spirochetes not producing this protein (17). Thus, when OspA is rapidly cleared from the spirochete surface, a proportion of the spirochete population may be free to leave the midgut and migrate to the salivary glands for transmission in saliva. The tick midgut protein that binds to OspA has not yet been described but should be an area of future research, as will be identifying factors that modulate the dispersal of spirochetes from the tick midgut (18).
Factors that regulate the switch from expression of OspA to OspC are likely varied and complex. Temperature is clearly one factor. As the tick finds a host and starts to feed, it moves from ambient temperature to the temperature at the surface of mammalian host skin. This rapid change in temperature clearly influences the spirochete population. Shifting spirochetes in vitro from lower temperatures to 37 [degrees] C induced OspC expression (14,19). Similarly, other spirochete proteins, such as the Erp lipoprotein lipoprotein (lĭp'əprō`tēn), any organic compound that is composed of both protein and the various fatty substances classed as lipids, including fatty acids and steroids such as cholesterol. family, are upregulated during temperature increase (20). Cell density also may regulate spirochete protein expression. In a series of experiments using anti-OspA antibody passively transferred to mice serving as hosts for infected nymphal ticks, decreased spirochete density resulting from antibody-mediated death was associated with a lack of expression of OspC (21). Similarly, growth phase affects the synthesis of various proteins, including OspC (22). A change in pH in vitro can influence the expression of many proteins, including OspC (23,24). When ticks ingest blood, the pH of the midgut decreases from 7.4 to 6.8, which acts interdependently with increasing cell density and increased temperature to promote the reciprocal expression of OspA and OspC (25). The expression locus of the variable-like sequence (vlsE) may also prove to be of interest, since heterogeneity at this site appears to increase when ticks start to feed (26).
Dissemination to the Salivary Glands
Different experimental strategies have been used to visualize spirochetes as they move from the tick midgut, through the hemolymph, and into the salivary glands before delivery to the host. Spirochetes present in hemolymph (7) and salivary glands have been directly visualized by electron microscopy (8). Indirect methods for detecting spirochetes in tick salivary glands included salivary gland explant cultures in BSK BSK Banashankari
BSK Biskra, Algeria - Biskra (Airport Code)
BSK Basking Shark (FAO fish species code)
BSK Brass Surround Kit (fireplace accessory) medium (Sigma Chemical Co., St. Louis, MO) and an infectivity assay of salivary gland homogenates inoculated into mice (27). These experiments demonstrated that although spirochetes were occasionally detected in salivary glands early during tick feeding, sufficient numbers of infectious spirochetes were not present within the salivary glands to cause infection in experimental hosts until at least 60 hours after tick attachment. Recently, confocal microscopy has allowed direct determination of specific spirochetal proteins synthesized in salivary glands. This approach has shown that small populations of spirochetes expressing OspA are present in the tick salivary glands and the dermis dermis: see skin. at the site of tick feeding early during the tick bloodmeal, but these spirochetes do not appear to be infectious. After 2 days of feeding, large numbers of spirochetes belonging to two predominant populations appear in the salivary glands and local dermis of the feeding site: spirochetes expressing only OspC, and spirochetes expressing neither OspA nor OspC (26). Infection of the host may be determined by actual numbers of spirochetes, the particular Osp phenotype entering the host from the tick, or both.
Transmission to Host and Duration of Tick Feeding
Most persons bitten by nymphal I. scapularis do not become infected with B. burgdorferi and do not become ill with Lyme disease. Although 25% to 30% of nymphal I. scapularis in the northeastern United States are infected with B. burgdorferi sensu stricto, only approximately 1% to 2% of persons with recognized bites by nymphal I. scapularis become infected. One reason for this low rate of infection is that most ticks are detected and removed before they transmit infectious spirochetes. Virtually no transmission occurs during the first day of nymphal feeding, inefficient transmission takes place during the second day of tick feeding, and transmission is extremely efficient during the third day of nymphal feeding (28,29). These observations are consistent with the timing of spirochete multiplication, switching of Osps, and dispersal within the tick. A basic understanding of tick-spirochete interactions and transmission dynamics clearly has important implications in the clinical setting. The fact that prompt tick removal aborts transmission of B. burgdorferi sensu stricto is an important reason why most physicians in Lyme disease-endemic areas do not prophylactically treat persons bitten by ticks. In Europe and Asia, where other tick species (I. ricinus and I. persulcatus) transmit several genospecies of spirochetes, the situation may be more complex, with some risk of transmission during the first day of tick attachment (30,31).
An important practical outgrowth of understanding how B. burgdorferi populations change during tick feeding is the enhanced insight into the molecular mechanisms of how the human Lyme disease vaccine based on OspA (32,33) works. Early on it was noticed that when anti-OspA antibody was present in the host at the time of tick attachment or during the first 24 hours of tick feeding, infection was prevented. If, however, antibodies were passively transferred to the host after this window of opportunity, infection was not prevented or cured with anti-OspA antibody (13,34). The implication was clear: spirochetes were killed inside the tick, before transmission to the host. Originally, it was suggested that anti-OspA antibodies actually sterilized ster·il·ize
tr.v. ster·il·ized, ster·il·iz·ing, ster·il·iz·es
1. To make free from live bacteria or other microorganisms.
2. the tick, eliminating all spirochetes present before they were transmitted (13). Subsequent studies with variable levels of anti-OspA antibody showed that ticks were only occasionally sterilized, at the highest levels of antibody in an immune host. More subtle effects were demonstrated with passively transferred anti-OspA antibody, which demonstrated that spirochete populations in the midgut were diminished but not eliminated. This diminution also prevented the switch from OspA expression to OspC expression and prevented dispersal of spirochetes to the salivary glands and transmission to the host (21). Thus, the action of anti-OspA antibody ingested by the tick had subtle effects on spirochete populations that blocked transmission to the host. Anti-OspC immunity appears to differ, acting in both the invertebrate invertebrate (ĭn'vûr`təbrət, –brāt'), any animal lacking a backbone. The invertebrates include the tunicates and lancelets of phylum Chordata, as well as all animal phyla other than Chordata. and vertebrate host (34,35). These studies are a prime example of how insight into basic vector-pathogen interactions can lead to development of important prevention tools used to combat human disease.
Tick-Borne Relapsing Fever
In 1857, Livingstone published his observations resulting from 16 years of exploration in southern Africa. In regions that are now Angola and Mozambique, he documented an illness of humans following the bite of a tick, known regionally as the "tampan" or "carapato." This brief description was the first written account of tick-borne relapsing fever caused by B. duttonii. The tick was described by Murray in 1877 and named Argas moubata, later revised within the genus Ornithodoros. In 1905, Dutton and Todd (36) reported that O. moubata transmitted spirochetes to monkeys while feeding on them--the first demonstration that ticks were capable vectors of relapsing fever spirochetes. Also included in this landmark work was the observation that spirochetes were present in both the midgut and malpighian tubules of infected ticks.
Relatively few studies have examined the distribution of relapsing fever spirochetes in tissues of argasid ticks. Most early investigations examined B. duttonii in O. moubata, expanding on the work of Dutton and Todd, and demonstrated spirochetes in numerous tick tissues including the midgut, synganglion (central ganglion ganglion: see nervous system.
Aggregate of nerve-cell bodies outside the central nervous system (CNS). The spinal ganglion contains the nerve-cell bodies of the nerve fibres that carry impulses toward the CNS (afferent neurons in dorsal ), malphigian tubules, salivary glands, ovaries Ovaries
The female sex organs that make eggs and female hormones.
Mentioned in: Choriocarcinoma
ovaries (ō´v , and coxal coxal (käkˑ·sl),
adj pertaining to the hip area. organs. Early investigators also demonstrated that B. duttonii is transmitted by contamination of infected coxal fluid and tick bite. Burgdorfer's study of B. duttonii in nymphal and adult O. moubata is one of the most thorough investigations of any relapsing fever spirochete (37). While confirming the infection of many tick tissues, Burgdorfer also showed that B. duttonii enters the hemolymph as early as 24 hours after ticks acquire spirochetes in their midgut by feeding on a spirochetemic mouse. Also, the mode of transmission varies with the stage of tick. Nymphal O. moubata transmit B. duttonii in the saliva; adults transmit primarily via the coxal fluid. This stage-dependent difference in the primary mode of transmission helped clarify earlier observations.
B. hermsii-Tick Interactions
Tick-borne relapsing fever was first reported in the United States in 1915, following the recognition of five human patients in Colorado (38). The tick vector for the causative spirochete lives in the higher elevations in western North America and was named O. hermsi in 1935 (39). Relapsing fever spirochetes transmitted by O. hermsi were first named Spirochaeta hermsi in 1942 and later changed to Borrelia hermsii in 1948. The criterion for naming the spirochete B. hermsii was based on the many observations in the laboratory by Davis (40). O. hermsi was capable of transmitting this spirochete while other species of ticks, O. turicata and O. parkeri, were not, although these other species of ticks were capable of transmitting other species of spirochetes (40). The mechanisms responsible for this strict species specificity for the transmissibility trans·mis·si·ble
That can be transmitted: transmissible signals.
trans·mis of one species of spirochete by only one species of tick are unknown.
B. hermsii infects a variety of small mammals living in coniferous forests at moderate to high elevations. The primary hosts for spirochetes and ticks are diurnal diurnal /di·ur·nal/ (di-er´nal) pertaining to or occurring during the daytime, or period of light.
1. Having a 24-hour period or cycle; daily.
2. rodents such as chipmunks and tree squirrels. Ticks living in the nests or crevices nearby feed on these hosts at night, taking their bloodmeal quickly within 15 to 90 minutes, then retreating to their off-host refuge. These ticks and other species of Ornithodoros can fast for months to many years and retain infectious spirochetes throughout a life cycle that may take years to complete (41). Therefore, ticks have a greater potential to maintain spirochetes in nature for prolonged periods than do individual mammalian hosts that are infective to new cohorts of ticks while intermittently spirochetemic for 14 to 30 days (42).
Although other, larger species of Ornithodoros excrete excrete /ex·crete/ (eks-kret´) to throw off or eliminate by a normal discharge, such as waste matter.
To eliminate waste material from the body. substantial amounts of coxal fluid while feeding, O. hermsi excretes little or none while on the host. Therefore the only efficient mechanism for O. hermsi to transmit B. hermsii is by bite (43). The larva larva, in zoology
larva, independent, immature animal that undergoes a profound change, or metamorphosis, to assume the typical adult form. Larvae occur in almost all of the animal phyla; because most are tiny or microscopic, they are rarely seen. , three to five nymphal stages, and adult O. hermsi are all capable of transmitting B. hermsii (43,44). Transovarial transmission is rare (43), so larvae in nature are unlikely to be infective during their blood meal.
The distribution of B. hermsii in organs and tissues of O. hermsi has received little attention. In 1942, Wheeler published the only study before 1998 that examined different tissues of O. hermsi for B. hermsii (45). Spirochetes were consistently found in the midgut but only occasionally seen in the hemocoel, muscles, and "esophagus" for up to 38 days after infection was initiated in ticks. No spirochetes were seen in the salivary glands. Yet, based on recent observations (46), Wheeler's negative data were most likely due to his use of thin sections and silver stain. The lack of specific immunologic stains for fluorescence microscopy 60 years ago made visualizing spirochetes much more difficult than today. Schwan and Hinnebusch (46) examined 41 O. hermsi from 33 to 144 days after infection with B. hermsii and found that the salivary glands from all ticks were infected. The midgut from 33 ticks and the synganglion from 22 ticks were also examined, and spirochetes were present in these organs from all ticks.
Antigenic Variation in Mammals and Ticks
During the last 20 years, many studies have examined the mechanism of antigenic variation of B. hermsii, which has been proclaimed as a spirochete adaptation to evade the mammalian host's immune response immune response
An integrated bodily response to an antigen, especially one mediated by lymphocytes and involving recognition of antigens by specific antibodies or previously sensitized lymphocytes. (47). The ability of the spirochete to evade immunologic destruction through antigenic variation within the mammal allows for the prolonged, recurrent bacteremias (Figure 2) that make spirochetes accessible to fast-feeding ticks and hence facilitate horizontal transmission horizontal transmission
Transmission of infection by contact.
horizontal transmission Epidemiology The transmission of an infection from one to another person of the same generation in the same population. of spirochetes in nature. A single cell of B. hermsii can give rise to 30 antigenic variants, each of which expresses a unique, variable major protein (Vmp) that confers a specific serotype serotype /se·ro·type/ (ser´o-tip) the type of a microorganism determined by its constituent antigens; a taxonomic subdivision based thereon.
v. (47,48). Other than the suggested role of immune evasion, no function has been demonstrated for these Vmps, which occur in two size classes, the variable large proteins (Vlps) and the variable small proteins (Vsps) (49). During mammalian infection, B. hermsii produces cyclic spirochetemias that may achieve a density of [10.sup.8] bacteria/mL of blood. Each acute phase of spirochetemia contains a population of spirochetes composed almost entirely of one serotype (48). Relapse populations are predominated by a serotype different from the population preceding or following it.
[FIGURE 2 OMITTED]
To address the influence of tick infection on the antigenic stability of spirochetes, two cohorts of O. hermsi were each infected with a different serotype of B. hermsii, serotype 7 or serotype 8 (46). The ticks were allowed to molt to the next stage and then fed individually on single mice. Eighteen (19%) of the 95 ticks transmitted spirochetes, and with every infection the first spirochetemia in mice had the same serotype ingested previously by the tick. Additional groups of ticks infected with the same serotypes were also examined. Polymerase chain reaction polymerase chain reaction (pŏl`ĭmərās') (PCR), laboratory process in which a particular DNA segment from a mixture of DNA chains is rapidly replicated, producing a large, readily analyzed sample of a piece of DNA; the process is (PCR PCR polymerase chain reaction.
polymerase chain reaction
Polymerase chain reaction (PCR) ) and restriction fragment length polymorphism restriction fragment length polymorphism
n. Abbr. RFLP
Intraspecies variations in the length of DNA fragments generated by the action of restriction enzymes and caused by mutations that alter the sites at which these enzymes act, changing analyses of the expression locus for the vmp genes showed that either the vlp7 or vsp8 gene was present, corresponding to the serotype of B. hermsii ingested by the tick. Cumulatively, these observations suggested that no serotype-related antigenic changes occurred in the spirochetes during infection in ticks. However, when single salivary glands from infected ticks were examined by immunofluorescence Immunofluorescence
A technique that uses a fluorochrome to indicate the occurrence of a specific antigen-antibody reaction. The fluorochrome labels either an antigen or an antibody. microscopy with anti-Vlp7 or anti-Vsp8 antibody, no spirochetes were seen. Immunofluorescence staining of the other salivary glands with other antibodies showed, however, that all the glands were infected with spirochetes and that the bacteria were now expressing Vsp33, an Osp known previously from only one culture-adapted strain of B. hermsii (50). When blood from a mouse infected with serotype 8 of B. hermsii was inoculated into culture medium and incubated at either 23 [degrees] C or 37 [degrees] C, spirochetes continued to express Vsp8 at 37 [degrees] C but switched to Vsp33 at 23 [degrees] C (46). Thus, both a transfer of spirochetes from the mammalian bloodstream to tick and a drop in environmental temperature in vitro brought about an antigenic switch from the bloodstream Vmp to Vsp33. Recently, double-label immunofluorescence staining of spirochetes in the midgut and salivary glands of O. hermsi demonstrated that spirochetes expressing Vsp33 were detectable [greater than or equal to] 28 days after ticks became infected (Figure 3). By 68 days after infection, essentially all the spirochetes in the salivary glands expressed Vsp33, while only a third of the spirochetes in the midgut did so.
[FIGURE 3 OMITTED]
From the observations reviewed above, one phenomenon shared by B. burgdorferi and B. hermsii is the synthesis of OspC and Vsp33 at the time these spirochetes are transmitted by tick bite. DNA DNA: see nucleic acid.
or deoxyribonucleic acid
One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes. and amino acid amino acid (əmē`nō), any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins. sequence analysis also shows that these proteins are homologous (51) and that antisera produced to the two proteins are cross-reactive (51-53). Several other species of Borrelia also contain a related gene or protein recognized with either Northern or Western blot Western blot
A technique developed in 1979 that is used to confirm ELISA results. HIV antigen is purified by electrophoresis and attached by blotting to a nylon or nitrocellulose filter. (53). Therefore, this family of surface proteins may be shared by all species of borreliae, which are spirochetes defined, in part, by their requirement for an arthropod arthropod
Any member of the largest phylum, Arthropoda, in the animal kingdom. Arthropoda consists of more than one million known invertebrate species in four subphyla: Uniramia (five classes, including insects), Chelicerata (three classes, including arachnids and horseshoe vector for transmission. Our hypothesis is that these proteins are involved in the transmission of these spirochetes from tick to vertebrate host.
The temporal synthesis of OspC and Vsp33 during spirochete infection in ticks is strikingly different between B. burgdorferi and B. hermsii, but appears to be adaptive to ixodid versus argasid ticks, which have considerably different feeding behaviors. Most nymphal I. scapularis take 3 to 4 days to feed whereas O. hermsi feed to repletion re·ple·tion
1. The condition of being fully supplied or completely filled.
2. A state of excessive fullness. in only 15 to 90 minutes. In free-living, unfed I. scapularis, B. burgdorferi is usually found only in the midgut and OspC is not expressed. However, following tick attachment B. burgdorferi replicates, downregulates OspA, disseminates from the midgut to salivary glands, synthesizes OspC, and is transmitted via the saliva after 2 to 4 days of feeding. An increase in temperature and the ingestion ingestion /in·ges·tion/ (-chun) the taking of food, drugs, etc., into the body by mouth.
1. The act of taking food and drink into the body by the mouth.
2. of blood, environmental cues associated with a free-living tick having attached and begun to feed on a host, stimulate a subpopulation sub·pop·u·la·tion
A part or subdivision of a population, especially one originating from some other population: microbial subpopulations.
Noun 1. of B. burgdorferi to transiently synthesize OspC during feeding. If OspC is required for transmission of B. burgdorferi by tick bite, there is ample time, because of the slow feeding behavior of Ixodes ticks, for both the dissemination of spirochetes from the midgut to the salivary glands and the novel synthesis of OspC. Numerous studies have shown that humans and experimental animals infected by tick bite seroconvert to OspC early, demonstrating that this protein is expressed in mammals for some undetermined period. In free-living, unfed O. hermsii, the distribution of B. hermsii in these ticks and their expression of Vsp33 are just the opposite, with spirochetes established in the salivary glands and nearly all expressing Vsp33. In the scenario with O. hermsi feeding for only minutes after encountering a host, there is no time for spirochetes to disseminate out of the midgut, penetrate the salivary glands to the salivary duct salivary duct
An intralobular duct found in salivary glands and involved in the production and transport of their secretions. Also called secretory duct. , and also synthesize a new Osp that may facilitate (or be required for) transmission. Hence B. hermsii is in a constant state of readiness See: defense readiness condition; weapons readiness state. for transmission that is comparable to the phenotype and localization Customizing software and documentation for a particular country. It includes the translation of menus and messages into the native spoken language as well as changes in the user interface to accommodate different alphabets and culture. See internationalization and l10n. displayed by B. burgdorferi only briefly during a few days of attachment by I. scapularis (Figure 4).
[FIGURE 4 OMITTED]
The phenotypic changes and dissemination shown by B. burgdorferi during transmission by tick bite point to several possible functions for OspC: dissemination from the midgut, infection of the salivary glands, or successful colonization in the mammal following delivery into the feeding lesion in the dermis. Because the changes in protein synthesis and movement of the spirochetes occur rapidly in the nymphal ticks, identifying the precise time when OspC is produced in relation to the spirochetes' movement in the tick is difficult to determine by microscopy. Quantitative reverse transcription-PCR may help increase sensitivity through detecting specific gene transcripts in different tick tissues sampled at different times. However, the events shown by B. hermsii during its dissemination in the tick are much more protracted pro·tract
tr.v. pro·tract·ed, pro·tract·ing, pro·tracts
1. To draw out or lengthen in time; prolong: disputants who needlessly protracted the negotiations.
2. and may shed some light on the function of OspC, Vsp33, or other proteins. Because it takes approximately 3 weeks or more for B. hermsii to disseminate and become established in the salivary glands of O. hermsi, immunofluorescent staining of these spirochetes in tick tissues at successive intervals after infection has recently shown that B. hermsii can infect the salivary glands before the upregulation of Vsp33. At least for this relapsing fever spirochete, Vsp33 does not appear to be needed either for dissemination from the gut or invasion of the salivary glands.
Additional species of Borrelia and their expression of Osps associated with transmission need to be examined. If OspC, Vsp33, or other proteins are required for transmission by ticks, we anticipate finding homologs to these proteins in other species associated with their transmission. Other relapsing fever spirochetes in Ornithodoros ticks, B. anserina in Argas ticks, and other borrelia associated with ixodid ticks will be fruitful tick-spirochete associations to study. A comparison of borrelial genomes will also be helpful when such sequences become available. Finally, with important advances being made recently to inactivate in·ac·ti·vate
1. To render nonfunctional.
2. To make quiescent.
in·acti·va and introduce genes in these spirochetes (54,55), experiments to examine the importance of specific proteins in various steps of the transmission cycle are on the horizon.
Table. Diseases caused by infection with Borrelia species Disease No. of species Arthropod vector Lyme disease 3 (a) Hard ticks (Ixodes spp.) Tick-borne relapsing 21 (b) Soft ticks (Ornithodoros fever spp.) Avian borreliosis 1 (c) Soft ticks (Argas spp.) Bovine borreliosis 1 (d) Hard ticks (Boophilus spp.) Louse-borne relapsing 1 (e) Body louse (Pediculus) fever (a) Borrelia burgdorferi, B. garinii, and B. afzelii are known human pathogens. (b) Some species of Borrelia associated with Ornithodoros ticks are of unknown pathogenicity. (c) B. anserina. (d) B. theileri. (e) B. recurrentis.
We thank Gary Hettrick for help with the figures and J.M. Musser, J. Carroll, and M. Chaussee for reviewing the manuscript.
(1.) Fraser CM, Casjens S, Huang WM, Sutton GG, Clayton R, Lathigra R, et al. Genomic sequence of a Lyme disease spirochaete Noun 1. spirochaete - parasitic or free-living bacteria; many pathogenic to humans and other animals
eubacteria, eubacterium, true bacteria - a large group of bacteria having rigid cell walls; motile types have flagella , Borrelia burgdorferi. Nature 1997;390:580-6.
(2.) Fraser CM, Norris SJ, Weinstock GM, White O, Sutton GG, Dodson R, et al. Complete genome sequence of Treponema pallidum, the syphilis spirochete. Science 1998;281:375-8, 87-8.
(3.) Schwan TG, Burgdorfer W, Rosa PA. Borrelia. In: Murray PR, Baron E J, Pfaller MA, Tenover FC, Yolken RH, editors. Manual of clinical microbiology. 7th ed. Washington: American Society for Microbiology The American Society for Microbiology (ASM) is a scientific organization, based in the United States although with over 43,000 members throughout the world. It is the largest single life science professional organization and its members include those whose interests encompass basic ; 1999. p. 746-58.
(4.) Felsenfeld O. Borrelia. Strains, vectors, human and animal borreliosis. St. Louis: Warren H. Green, Inc.; 1971.
(5.) Burgdorfer W, Barbour AG, Hayes SF, Benach JL, Grunwaldt E, Davis JP. Lyme disease--a tick-borne spirochetosis spirochetosis /spi·ro·che·to·sis/ (-ke-to´sis) infection with spirochetes.
n. pl. ? Science 1982;216:1317-9.
(6.) Burgdorfer W, Hayes SF, Corwin D. Pathophysiology pathophysiology /patho·phys·i·ol·o·gy/ (-fiz?e-ol´ah-je) the physiology of disordered function.
1. of the Lyme disease spirochete, Borrelia burgdorferi, in ixodid ticks. Rev Infect Dis 1989; 11 (Suppl. 6): S1442-S1450.
(7.) Benach JL, Coleman JL, Skinner RA, Bosler EM. Adult Ixodes dammini Ixodes dam·mi·ni
A species of Ixodes that is a vector of Lyme disease and human babesiosis in the United States.
tick on rabbits: a hypothesis for the development and transmission of Borrelia burgdorferi. J Infect Dis 1987;155:1300-6.
(8.) Zung JL, Lewengrub S, Rudzinska MA, Spielman A, Telford SR, Piesman J. Fine structural evidence for the penetration of the Lyme disease spirochete Borrelia burgdorferi through the gut and salivary sal·i·var·y
1. Of, relating to, or producing saliva.
2. Of or relating to a salivary gland.
pertaining to the saliva. tissues of Ixodes dammini. Can J Zool 1989;67:1737-48.
(9.) Ribeiro JMC JMC Joint Military Commission
JMC Jefferson Medical College
JMC Jax Money Crew (computer gaming)
JMC Joint Munitions Command (US Army; Rock Island Arsenal, Rock Island IL)
JMC James Madison College , Mather TN, Piesman J, Spielman A. Dissemination and salivary delivery of Lyme disease spirochetes in vector ticks (Acari: Ixodidae). J Med Entomol 1987;24:201-5.
(10.) Piesman J, Oliver JR, Sinsky RJ. Growth kinetics of the Lyme disease spirochete (Borrelia burgdorferi) in vector ticks (Ixodes dammini). Am J Trop Med Hyg 1990;42:352-7.
(11.) Burkot TR, Piesman J, Wirtz RA. Quantitation of the Borrelia burgdorferi outer surface protein A in Ixodes scapularis: fluctuations during the tick life cycle, doubling times and loss while feeding. J Infect Dis 1994;170:883-9.
(12.) de Silva AM, Fikrig E. Growth and migration of Borrelia burgdorferi in Ixodes ticks during blood feeding. Am J Trop Med Hyg 1995;53:397-404.
(13.) de Silva AM, Telford SR III, Brunet LR, Barthold SW, Fikrig E. Borrelia burgdorferi OspA is an arthropod-specific transmission-blocking Lyme disease vaccine. J Exp Med 1996;183:271-5.
(14.) Schwan TG, Piesman J. Temporal changes in outer surface proteins A and C of the Lyme disease-associated spirochete, Borrelia burgdorferi, during the chain of infection in ticks and mice. J Clin Microbiol 2000;38:382-8.
(15.) Schwan TG, Piesman J, Golde WT, Dolan MC, Rosa PA. Induction of an outer surface protein on Borrelia burgdorferi during tick feeding. Proc Natl Acad Sci U S A 1995;92:2909-13.
(16.) Pal U, de Silva AM, Montgomery RR, Fish D, Anguita J, Anderson JF, et al. Attachment of Borrelia burgdorferi within Ixodes scapularis mediated by outer surface protein A. J Clin Invest 2000;106:561-9.
(17.) Fingerle V, Laux H, Munderloh UG, Schulte-Spechtel U, Wilske B. Differential expression of outer surface proteins A and C by individual Borrelia burgdorferi in different genospecies. Med Microbiol Immunol 2000;189:59-66.
(18.) Coleman JL, Gebbia JA, Piesman J, Degen JL, Bugge TH, Benach JL. Plasminogen plasminogen /plas·min·o·gen/ (plaz-min´ah-jen) the inactive precursor of plasmin, occurring in plasma and converted to plasmin by the action of urokinase.
n. is required for efficient dissemination of B. burgdorferi in ticks and for enhancement of spirochetemia in mice. Cell 1997;89:1111-9.
(19.) Schwan TG, Gage KL, Hinnebusch BJ. Analysis of relapsing fever spirochetes from the western United States Noun 1. western United States - the region of the United States lying to the west of the Mississippi River
Santa Fe Trail - a trail that extends from Missouri to New Mexico; an important route for settlers moving west in the 19th century . Journal of Spirochetal and Tick-Borne Diseases 1995;2:3-8.
(20.) Stevenson B, Bono JL, Schwan TG, Rosa P. Borrelia burgdorferi Erp proteins are immunogenic im·mu·no·gen·ic
Producing an immune response.
producing immunity; evoking an immune response. in mammals infected by tick bite, and their synthesis is inducible in cultured bacteria. Infect Immun 1998;66:2648-54.
(21.) de Silva AM, Zeidner NS, Zhang Y, Dolan MC, Piesman J, Fikrig E. Influence of outer surface protein A antibody on Borrelia burgdorferi within feeding ticks. Infect Immun 1999;67:30-5.
(22.) Ramamoorthy R, Philipp MT. Differential expression of Borrelia burgdorferi proteins during growth in vitro. Infect Immun 1998;66:5119-24.
(23.) Carroll JA, Garon CF, Schwan TG. Effects of environmental pH on membrane proteins in Borrelia burgdorferi. Infect Immun 1999;67:3181-7.
(24.) Carroll JA, Cordova Cordova, Spain: see Córdoba. , RM, Garon CF. Identification of 11 pH-regulated genes in Borrelia burgdorferi localizing to linear plasmids. Infect Immun 2000;68:6677-84.
(25.) Yang X, Goldberg MS, Popova TG, Schoeler GB, Wikel SK, Hagman KE, et al. Interdependence of environmental factors influencing reciprocal patterns of gene expression in virulent Borrelia burgdorferi. Mol Microbiol 2000;37:1470-9.
(26.) Ohnishi J, Piesman J, de Silva AM. Antigenic and genetic heterogeneity of Borrelia burgdorferi populations transmitted by ticks. Proc Natl Acad Sci U S A 2001;98:670-5.
(27.) Piesman J. Dispersal of the Lyme disease spirochete Borrelia burgdorferi to salivary glands of feeding nymphal Ixodes scapularis (Acari: Ixodidae). J Med Entomol 1995;32:519-21.
(28.) Piesman J, Mather TN, Sinsky RJ, Spielman A. Duration of tick attachment and Borrelia burgdorferi transmission. J Clin Microbiol 1987;25:557-8.
(29.) Piesman J. Dynamics of Borrelia burgdorferi transmission by nymphal Ixodes dammini ticks. J Infect Dis 1993;167:1082-5.
(30.) Kahl O, Janetzki-Mittmann C, Gray JS, Jonas R, Stein J, de Boer R. 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. Zentralbl Bakteriol 1998;287:41-52.
(31.) Korenberg EI, Moskvitina GG, Vorobryeva NN. Prevention of human borreliosis after infected tick's bite. In: Cevenini R, Sambri V, la Placa M, editors. VI International Conference on Lyme Borreliosis Lyme borreliosis
Another name for Lyme disease.
Mentioned in: Lyme Disease , 1994; Bologna, Italy: the University of Bologna Nowadays, the University counts about 100,000 students in its 23 faculties. It has branch centers in Reggio nell'Emilia, Imola, Ravenna, Forlì, Cesena and Rimini and a branch center abroad in Buenos Aires. ;1994. p. 209-11.
(32.) Steere AC, Sikand VK, Meurice F, Parenti DL, Fikrig E, Schoen RT, et al. Vaccination against Lyme disease with recombinant Borrelia burgdorferi outer-surface lipoprotein A with adjuvant adjuvant /ad·ju·vant/ (aj?dbobr-vant) (a-joo´vant)
1. assisting or aiding.
2. a substance that aids another, such as an auxiliary remedy.
3. . N Engl J Med 1998;339:209-15.
(33.) Sigal LH, Zahradnik JM, Lavin P, Patella patella (pətĕl`ə): see kneecap. SJ, Bryant G, Haselby H, et al. A vaccine consisting of recombinant Borrelia burgdorferi outer surface protein A to prevent Lyme disease. N Engl J Med 1998;339:216-22.
(34.) Zhong W, Stehle T, Museteanu C, Siebers A, Gem L, Kramer M, et al. Therapeutic passive vaccination against chronic Lyme disease chronic Lyme disease A predominantly neurologic condition ranging from mild–eg, fatigue, paresthesia, arthralgia, memory loss, mood swings, and dysomnia, to severe–eg, spastic paraparesis, tetraparesis, ataxia, chorea, cognitive impairment, bladder in mice. Proc Natl Acad Sci U S A 1997;94:12533-8.
(35.) Gilmore RD, Piesman J. Inhibition of Borrelia burgdorferi migration from the midgut to the salivary glands following feeding by ticks on OspC-immunized mice. Infect Immun 2000;68:411-4.
(36.) Dutton JE, Todd JL. The nature of human tick-fever in the eastern part of the Congo Free State Congo Free State
See Congo. with notes on the distribution and bionomics bi·o·nom·ics
n. (used with a sing. verb)
[From French bionomique, pertaining to ecology, from bionomie, ecology : Greek bio-, bio- of the tick. Liverpool School of Tropical Medicine-Memoir XVII. 1905;17:1-18.
(37.) Burgdorfer W. Analyse des Infektionsverlaufes bei Ornithodorus moubata (Murray) und der naturlichen Uebertragung von Spirochaeta duttoni. Acta Trop 1951;8:194-262.
(38.) Meador CN. Five cases of relapsing fever originating in Colorado, with positive blood findings in two. Colorado Medicine 1915;12:365-9.
(39.) Wheeler CM. A new species of tick which is a vector of relapsing fever in California. Am J Trop Med 1935;15:435-8.
(40.) Davis GE. Species unity or plurality of the relapsing fever spirochetes. In: Moulton FR, editor. A symposium on relapsing fever in the Americas. Washington: American Association for the Advancement of Science American Association for the Advancement of Science (AAAS), private organization devoted to furthering the work of scientists and improving the effectiveness of science in the promotion of human welfare. ; 1942. p. 41-7.
(41.) Francis E. Longevity of the tick Ornithodoros turicata and of Spirochaeta recurrentis within this tick. Public Health Rep 1938;53:2220-41.
(42.) Burgdorfer W, Mavros AJ. Susceptibility of various species of rodents to the relapsing fever spirochete, Borrelia hermsii. Infect Immun 1970;2:256-9.
(43.) Herms WB, Wheeler CM. Tick transmission of California relapsing fever. J Econ Entomol 1935;28:846-55.
(44.) Herms WB, Wheeler CM. Ornithodoros hermsi Wheeler as a vector of relapsing fever in California. J Parasitol 1936;22:276-82.
(45.) Wheeler CM. The distribution of the spirochete of California relapsing fever within the body of the vector, Ornithodoros hermsi. In: Moulton FR, editor. A symposium on relapsing fever in the Americas. Washington: American Association for the Advancement of Science; 1942. p. 89-99.
(46.) Schwan TG, Hinnebusch BJ. Bloodstream- versus tick-associated variants of a relapsing fever bacterium. Science 1998;280:1938-40.
(47.) Barbour AG, Restrepo BI. Antigenic variation in vector-borne pathogens. Emerg Infect Dis 2000;6:449-57.
(48.) Stoenner HG, Dodd T, Larsen C. Antigenic variation in B. hermsii. J Exp Med 1982;156:1297-311.
(49.) Cadavid D, Pennington PM, Kerentseva TA, Bergstrom S, Barbour AG. Immunologic and genetic analyses of VmpA of a neurotropic neurotropic
pertaining to or emanating from neurotrophy, e.g. neurotropic osteopathy. strain of Borrelia turicatae. Infect Immun 1997;65:3352-60.
(50.) Barbour AG, Tessier SL, Stoenner HG. Variable major proteins of Borrelia hermsii. J Exp Med 1982;156:1312-24.
(51.) Carter CJ, Bergstrom S, Norris SJ, Barbour AG. A family of surface-exposed proteins of 20 kilodaltons in the genus Borrelia. Infect Immun 1994;62:2792-9.
(52.) Wilske B, Preac-Mursic V, Jauris S, Hofmann A, Pradel I, Soutschek E, et al. Immunological and molecular polymorphisms of OspC, an immunodominant major outer surface protein of Borrelia burgdorferi. Infect Immun 1993;61:2182-91.
(53.) Marconi RT, Samuels DS, Schwan TG, Garon CT. Identification of a protein in several Borrelia species which is related to OspC of the Lyme disease spirochetes. J Clin Microbiol 1993;31:2577-83.
(54.) Bono JL, Elias AF, Kupko III JJ, Stevenson B, Tilly K, Rosa P. Efficient targeted mutagenesis mutagenesis /mu·ta·gen·e·sis/ (mu?tah-jen´e-sis)
1. the production of change.
2. the induction of genetic mutation.
n. pl. in Borrelia burgdorferi. J Bacteriol 2000;182:2445-52.
(55.) Stewart PE, Thalken R, Bono JL, Rosa P. Isolation of a circular plasmid region sufficient for autonomous replication and transformation of infectious Borrelia burgdorferi. Mol Microbiol 2001;39:714-21.
Address for correspondence: Tom G. Schwan, Laboratory of Human Bacterial Pathogenesis, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, 903 S. 4th St., Hamilton, MT 59840 USA; fax: 406-363-9445; e-mail: email@example.com
Tom G. Schwan * and Joseph Piesman ([dagger])
* National Institutes of Health, Hamilton, Montana, USA; and ([dagger]) Centers for Disease Control and Prevention Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center. , Fort Collins, Colorado The City of Fort Collins, a home rule municipality situated on the Cache la Poudre River along the Colorado Front Range, is the county seat and most populous city in Larimer County, Colorado. , USA
Dr. Schwan is a Senior Investigator in the Laboratory of Human Bacterial Pathogenesis at the Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases. His research interests include medical entomology, the serodiagnosis serodiagnosis /se·ro·di·ag·no·sis/ (-di?ag-no´sis) diagnosis of disease based on serologic tests.serodiagnos´tic
n. pl. of vector-borne infections, and how bacterial pathogens adapt for their biological transmission by ticks and fleas.
Dr. Piesman is Chief of the Lyme Disease Vector Section in the Bacterial Zoonoses Zoonoses
Infections of humans caused by the transmission of disease agents that naturally live in animals. People become infected when they unwittingly intrude into the life cycle of the disease agent and become unnatural hosts. Branch of the Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention. His research interests include the ecology and control of Lyme disease vectors, the biology of ticks, disease prevention, and the mechanisms of spirochete transmission by ixodid ticks.