Borrelia Infections: Lyme Disease and Relapsing Fever

Epidemiology and Transmission

B. burgdorferi is transmitted by species of ticks of the Ixodes genus. In the United States, the usual vector in the Northeast and the upper Midwest is Ixodes scapularis (the deer tick or black-legged tick), whereas Ixodes pacificus (the western black-legged tick) is the usual vector on the Pacific Coast. In Europe, the most important vector for the spirochete is Ixodes ricinus, which commonly feeds on sheep and cattle.

The life cycle of I. scapularis consists of three stages—larva, nymph, and adult—that develop during a 2-year period. Ticks feed once during each stage of the life cycle. The larvae emerge in the early summer from eggs laid in the spring by the adult female tick. Greater than 95% of the larvae are born uninfected with B. burgdorferi because transovarial transmission rarely occurs. The larvae feed on a wide variety of small mammals, such as the white-footed mouse, that are natural reservoirs for B. burgdorferi . Tick larvae become infected by feeding on animals that are infected with the spirochete. The tick emerges the following spring in the nymphal stage. This stage of the tick is most likely to transmit infections to humans, presumably because it is active at times during which humans are most likely to be in tick-infested areas and because it is very small and difficult to see. Consequently, the tick is more likely to be able to feed for a relatively long time, which increases the likelihood of transmission. If the nymphal tick is not infected with B. burgdorferi, it may subsequently become infected if it feeds on an infected animal during this stage of its development. The nymphs molt in the late summer or early fall and reemerge as adults. If the adult is infected, it also may transmit B. burgdorferi to humans. The adult deer tick may breed and spend the winter on a white-tailed deer (hence its name). In areas of abundant deer, decreasing the deer population may result in a parallel decrease of the deer tick population. In the spring, the females lay their eggs and die, completing the 2-year life cycle. The density of the deer tick population varies based on geography, the deer population, and the weather.

Numerous factors are associated with the risk of transmission of B. burgdorferi from infected ticks to humans. The proportion of infected ticks varies greatly by geographic area and by the stage of the tick in its life cycle. I. pacificus often feeds on lizards, which are not a competent reservoir for B. burgdorferi . Consequently, less than 5% of these ticks are infected with B. burgdorferi, so Lyme disease is rare in the Pacific states. By contrast, I. scapularis feeds on small mammals (usually field mice), which are competent reservoirs for B. burgdorferi . As a result, in highly endemic areas, the rates of infection for different stages of deer ticks are, approximately, 2% for larvae, 15% to 30% for nymphs, and 30% to 50% for adults.

B. burgdorferi is transmitted when an infected tick inoculates saliva into the blood vessels of the skin of its host. The risk of transmission of B. burgdorferi from infected deer ticks is related to the duration of feeding. It takes hours for the mouthparts of ticks to implant in the host, and much longer (days) for the tick to become fully engorged from feeding. B. burgdorferi is found primarily in the midgut of the tick, but as the tick feeds and becomes engorged, the bacteria migrate to the salivary glands, from which they can be transmitted. Experiments with animals have shown that infected nymph-stage ticks must feed for 48 hours or longer, and infected adult ticks must feed for 72 hours or longer before the risk of transmission of B. burgdorferi becomes substantial. Results of a study of transmission of Lyme disease to humans are consistent with these experimental results. Among persons bitten by nymph-stage ticks, for which the duration of feeding could be estimated, the risk of Lyme disease was 0% among persons bitten by nymphs that had fed for less than 72 hours but was 25% among persons bitten by nymphs that had fed for 72 hours or more. Approximately 75% of persons who recognize that they have been bitten by a deer tick remove the tick within 48 hours after it has begun to feed, which may explain why only a small proportion of persons who recognize that they have been bitten by deer ticks subsequently develop Lyme disease. The risk of Lyme disease is greater from unrecognized bites because, in such instances, the tick is able to feed until fully engorged.

Substantial evidence indicates that the risk of Lyme disease after a recognized deer tick bite, even in hyperendemic areas, is only 1% to 3%. The expertise to identify the species, stage, and degree of engorgement of a tick and to assess the degree of risk is rarely available to individuals who are bitten. The dog or wood tick, which does not transmit Lyme disease, is more than twice as large as the deer tick; however, subjects frequently misidentify dog ticks as deer ticks. Many “ticks” submitted for identification by physicians turned out actually to be spiders, lice, scabs, or dirt, none of which can transmit Lyme disease. In addition, estimates by patients of the duration for which the tick fed or degree of engorgement are unreliable.

Lyme disease occurs throughout the world ( Fig. 17-1 ). In the United States, greater than 95% of cases of Lyme disease occur in 12 eastern states—Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Maryland, Delaware, and Virginia—and two Midwestern states—Minnesota and Wisconsin ( Fig. 17-2 ). In Europe, most cases occur in the Scandinavian countries and in central Europe (especially in Germany, Austria, and Switzerland), although cases have been reported from throughout the region.

Although an increase in frequency and an expansion of the geographic distribution of Lyme disease in the United States have occurred in recent years, the incidence of Lyme disease even in endemic areas varies substantially from region to region and within local areas. Information about the incidence of the disease is complicated by reliance, in most instances, on passive reporting of cases and by the high frequency of misdiagnosis of the disease. From 2003 through 2012, approximately 30,000 cases of Lyme disease were reported to the CDC each year ( Fig. 17-3 ), but ongoing studies suggest that the true number of Americans diagnosed with Lyme disease approaches 300,000 yearly.

Microbiology

The spirochetal bacterium B. burgdorferi is a fastidious, microaerophilic organism that in vitro must be grown on special media. It is slow growing, with a cell membrane that is covered by flagella and a loosely associated outer membrane. Major antigens of the bacteria include the outer surface lipoproteins OspA, OspB, and OspC (highly charged basic proteins of molecular masses of about 31 kDa, 34 kDa, and 23 kDa, respectively) and the 41-kDa flagellar protein. The organism is more properly classified as the Borrelia burgdorferi sensu lato (“in the broad sense”) species complex, which has been subclassified into several genomospecies, among which the major ones that cause human diseases are Borrelia burgdorferi sensu stricto (“in the strict sense”), Borrelia garinii, and Borrelia afzelii . In the United States, only B. burgdorferi sensu stricto has been isolated from humans. By contrast, substantial variability exists in the species of B. burgdorferi isolated from humans in Europe, most of which are either B. garinii or B. afzelii . The complete genome of the organism has been sequenced. The biology of B. burgdorferi is complex, as might be expected in view of the complicated life cycle of this vector-borne bacterium, part of which is spent in ticks (with a primitive immune system) and part of which is spent in mammals, which have a highly evolved immune system. The reader is referred to other sources for detailed discussion of the genetics and physiology of this organism.

Pathogenesis and Pathology

In approximately 90% of patients in the United States, Lyme disease begins with the characteristic expanding skin lesion, erythema migrans, at the site of the tick bite. During the development of the initial erythema migrans, the spirochete disseminates via the bloodstream; this may be asymptomatic or may be characterized by malaise, fatigue, headache, arthralgia, myalgia, fever, and regional lymphadenopathy. Days to weeks after the tick bite, infection may be clinically manifested in the skin as multiple erythema migrans. Then weeks to months after the initial infection clinical infection may involve the nervous system, heart, and/or the joints. The ability of the spirochete to spread through skin and other tissues may be facilitated by the binding of human plasminogen and its activators to the surface of the organism. During dissemination, B. burgdorferi attaches to certain host integrins, matrix glycosaminoglycans, and extracellular matrix proteins, which may explain the organism’s particular tissue tropisms (e.g., collagen fibrils in the extracellular matrix in the heart, nervous system, and joints). In addition, the sequences of OspC vary considerably among strains, and only a few groups of sequences are associated with disseminated disease.

Studies in mice have shown the importance of inflammatory innate immune responses in controlling early disseminated Lyme disease. In humans with erythema migrans, infiltrates of macrophages and T cells produce inflammatory and antiinflammatory cytokines. In addition, evidence suggests that in disseminated infections, adaptive T-cell and B-cell responses in lymph nodes produce antibodies against many components of the spirochete.

The mechanism by which B. burgdorferi interacts with the host immune responses to produce Lyme neuroborreliosis or Lyme arthritis is not fully understood. In the initial attempt to eliminate B. burgdorferi, the innate immune response to the organism results in the release of cytokines, chemokines, and other immune mediators that produce an inflammatory response. This inflammatory response damages host tissues in the process of attempting to eradicate the Borrelia organisms. Subsequently, an adaptive immune response is initiated through the processing and presentation of B. burgdorferi antigens by macrophages and dendritic cells. This response results in the release of additional immune mediators, which further exacerbate the damage produced by the inflammatory response.

Several spirochetes have the ability to cause transplacental infections in various animals and in humans. Transplacental transmission of B. burgdorferi has been documented in several animal studies, including case reports, case series, and transmission studies. B. burgdorferi has been cultured from fetal tissues of a coyote and a white-footed mouse and from the blood of a newborn calf. The presence of B. burgdorferi in fetal tissues of a white-footed mouse and a house mouse also has been shown by polymerase chain reaction (PCR) assay. Serologic evaluations also have been used to document in utero fetal infection with B. burgdorferi in an aborted calf, a newborn foal, and four beagle pups. Several animal studies have linked infection with B. burgdorferi during pregnancy with fetal wastage and reproductive failure in cows and beagles. Infection with B. burgdorferi during pregnancy also has been associated with reproductive failure and severe fetal infection in horses and with increased fetal loss in mice.

In animal experiments, transplacental transmission of B. burgdorferi was documented by PCR assay in 19 of 40 pups born to female beagles that had been intradermally inoculated with this spirochete multiple times during pregnancy. Only 4 of the 19 pups had culture-positive tissues, and none of the pups had any evidence of inflammation. In other studies, neither female rats inoculated with B. burgdorferi intraperitoneally at 4 days of gestation nor pregnant hamsters infected by tick bite just before gestation showed any culture evidence of transplacental transmission of B. burgdorferi to their offspring. In another study, offspring of naturally infected white-footed mice were unable to transmit B. burgdorferi to spirochete-free deer ticks allowed to feed on them.

Transplacental transmission of B. burgdorferi in humans has been shown in association with adverse fetal outcome in several case reports. The first was a report by Schlesinger and coworkers in 1985 that described a 28-year-old woman with untreated Lyme disease during the first trimester of pregnancy and who gave birth at 35 weeks of gestation to an infant with widespread cardiovascular abnormalities. The infant died during the first week of life, and postmortem examination showed spirochetes morphologically compatible with B. burgdorferi in the infant’s spleen, kidneys, and bone marrow but not in the heart. In contrast with the mononuclear cell infiltrate and proliferation of fibroblasts usually seen with congenital syphilis, there was no evidence of inflammation, necrosis, or granuloma formation in the infant’s heart or other organs. In 1987, MacDonald and coworkers described a 24-year-old woman with untreated Lyme disease in the first trimester of pregnancy who gave birth at term to a stillborn infant weighing 2500 g. B. burgdorferi was cultured from the liver, and spirochetes were seen in the heart, adrenal glands, liver, brain, and placenta with immunofluorescence and silver staining techniques. No evidence of inflammation was seen, however, and no abnormalities were noted except for a small ventricular septal defect.

Weber and colleagues in 1988 described a 37-year-old woman who received penicillin orally for 1 week for erythema migrans during the first trimester of pregnancy. She subsequently gave birth to a 3400-g at-term infant who died at 23 hours of age of what was described as “perinatal brain damage.” B. burgdorferi was subsequently identified in the newborn’s brain by using immunochromogenic staining with monoclonal antibodies. However, on postmortem examination, no significant inflammation or other abnormalities were found in any organ, including the brain. In 1997, Trevisan and associates described an otherwise healthy infant who presented with multiple annular erythematous lesions, fever, and generalized lymphadenopathy at 3 weeks of age. These clinical abnormalities recurred throughout the first 3 years of life despite oral therapy with amoxicillin and the macrolide antibiotic josamycin. A skin biopsy specimen revealed spirochetes by silver stain and was positive for B. burgdorferi by PCR assay. In addition, serologic studies were positive for infection with B. burgdorferi . The patient’s mother had no history of either a tick bite or Lyme disease, but she had been involved in outdoor activities in an endemic area and had a weakly positive serologic test for Lyme disease.

Several case reports have described pregnant women with either erythema migrans or neuroborreliosis who received appropriate antimicrobial therapy at different stages of their pregnancies. In none of these reports was there an association between Lyme disease in the mother and an adverse outcome of the pregnancy.

Transplacental transmission of B. burgdorferi also has been investigated in a study of 60 placentas from asymptomatic women who lived in an area endemic for Lyme disease and whose results on serologic testing by enzyme-linked immunosorbent assay (ELISA) were either positive or equivocal for antibodies to B. burgdorferi . All 60 placentas were examined with a Warthin-Starry silver stain for evidence of infection with B. burgdorferi ; 3 (5%) were positive for spirochetes. PCR assays for B. burgdorferi nucleotide sequences were performed on 2 of these 3 placentas and were positive in both. The women from whom these 3 placentas were obtained all had equivocal results on ELISAs and negative results on Western blot analysis for Lyme disease and negative results on serologic tests for syphilis. In addition, none of these women had a history of either a tick bite or a clinical course consistent with Lyme disease. All of these pregnancies had entirely normal outcomes.

In addition to the individual case reports, several published case series have assessed the relationship between Lyme disease in pregnant women and fetal outcomes. Two of these case series were conducted by the CDC. The first was a retrospective investigation conducted in 19 women with Lyme disease during pregnancy and who were identified by the investigators without knowing the fetal outcomes. The adverse outcomes included prematurity, cortical blindness, intrauterine fetal death, syndactyly, and a generalized neonatal rash. Infection with B. burgdorferi could not be directly implicated as the cause of any of these outcomes. The second case series included 17 women who acquired Lyme disease during pregnancy and were evaluated prospectively. One woman had a spontaneous abortion with no evidence of an infection with B. burgdorferi on either stains or cultures of the fetal tissue, 1 woman had an infant with isolated syndactyly, and 15 women were delivered of normal infants with no clinical or serologic evidence of infection with B. burgdorferi .

In 1999, Maraspin and coworkers reported a series of 105 women with erythema migrans during pregnancy. Ninety-three (88.6%) of the 105 women had healthy infants delivered at term, 2 (1.9%) pregnancies ended with a miscarriage, and 6 (5.7%) ended with a preterm birth. One of the preterm infants had cardiac abnormalities, and two died shortly after birth. Four (3.8%) infants born at term had congenital anomalies (one with syndactyly and three with urologic abnormalities). As with a previous study, infection with B. burgdorferi could not be directly implicated as the cause of any of these adverse outcomes.

Several epidemiologic studies of Lyme disease during pregnancy also have been conducted. In the first, Williams examined 421 serum specimens obtained from cord blood and found no association between the presence of immunoglobulin G (IgG) antibodies to B. burgdorferi and congenital malformations. In another study, Nadal and associates investigated outcomes in 1434 infants of 1416 women for the presence of antibodies to B. burgdorferi at the time of delivery. Of the women, 12 (0.85%) were found to be seropositive, but only 1 woman had a history consistent with Lyme disease during pregnancy. Of the infants born to the 12 seropositive women, 2 had transient hyperbilirubinemia, 1 had transient hypotonia, 1 was postterm and small for gestational age with evidence of chronic placental insufficiency, 1 had transient macrocephaly, and 1 had transient supraventricular extra beats. The infant born to the woman with a clinical history of Lyme disease during pregnancy had a ventricular septal defect. At follow-up evaluations, approximately 9 to 17 months later, all of the children, except for the child with the cardiac defect, were entirely well, and none had serologic evidence of infection with B. burgdorferi .

In 1994, Gerber and Zalneraitis surveyed neurologists in areas of the United States in which Lyme disease was endemic at that time to determine how many had seen a child with clinically significant neurologic disease whose mother had been diagnosed as having Lyme disease during pregnancy. None of the 162 pediatric and 37 adult neurologists who responded to the survey had ever seen a child whose mother had been diagnosed with Lyme disease during pregnancy. The investigators concluded that congenital neuroborreliosis was either not occurring or occurring at an extremely low frequency in areas endemic for Lyme disease. In a retrospective case-control study carried out in an area endemic for Lyme disease, 796 “case” children with congenital cardiac anomalies were compared with 704 “control” children without cardiac defects with respect to Lyme disease in their mothers either during or before the pregnancy. No association was found between congenital heart defects and either a tick bite or Lyme disease in the mothers either within 3 months of conception or during pregnancy.

Investigators in New York performed two studies of the relationship between Lyme disease in pregnant women and adverse outcomes of the pregnancies. The first was an unselected, prospective, population-based investigation in an area endemic for Lyme disease in which approximately 2000 women in Westchester County, New York, were evaluated for clinical and serologic evidence of Lyme disease at the first prenatal visit and again at delivery. Of these women, 11 (0.7%) were seropositive, and 79 (4%) reported at the first prenatal visit that they had had Lyme disease sometime in the past. One woman with an untreated influenza-like illness in the second trimester had a negative result on serologic testing for Lyme disease at the prenatal visit but a positive result at delivery. In addition, during the study period, clinical Lyme disease was diagnosed in 15 pregnant women. No association was found between exposure of the mother to B. burgdorferi either before conception or during pregnancy and fetal death, prematurity, or congenital malformations. In the second study, the researchers compared 5000 infants, half from an area in which Lyme disease was endemic and half from an area without Lyme disease, who served as control subjects. The researchers found no significant difference in the overall incidence of congenital malformations between the two groups. Although there was a statistically significant higher rate of cardiac malformations in the endemic area compared with that in the control area, no relationship was noted between a cardiac malformation and either a clinical history or serologic evidence of Lyme disease. The researchers concluded from the findings of these two studies that a pregnant woman with a past infection with B. burgdorferi, either treated or untreated, did not have an increased risk of early fetal loss or of having a low-birth-weight infant or an infant with congenital malformations.

Two reports have documented the presence of B. burgdorferi in cow’s milk. In 1988, Burgess cultured B. burgdorferi from 1 of 3 samples of colostrum from cows but from none of 44 samples of cow’s milk. Lischer and colleagues used a PCR assay to identify nucleotide sequences of B. burgdorferi in the milk of a cow with clinical Lyme disease. In a similar investigation of human milk, Schmidt and coworkers examined breast milk from two lactating women with erythema migrans and from three lactating women with no clinical evidence of Lyme disease. The breast milk samples from both women with erythema migrans tested positive for B. burgdorferi by PCR assay, whereas the breast milk samples from all three healthy women tested negative. No other reports have corroborated these findings in human milk. B. burgdorferi has never been cultured from breast milk, and transmission of Lyme disease through breastfeeding has never been documented.

Clinical Manifestations

The clinical manifestations of Lyme disease depend on the stage of the illness: early localized disease, early disseminated disease, or late disease. Erythema migrans, the manifestation of early localized Lyme disease, appears at the site of the tick bite, 3 to 30 days (typically 7-10 days) after the bite. Erythema migrans is found in about 90% of patients with objective evidence of infection with B. burgdorferi . In a prospective study of 10,936 subjects given Lyme vaccine versus placebo, 147 subjects developed definite Lyme disease and 142 of 147 (97%) presented with erythema migrans. Erythema migrans begins as a red macule or papule and expands for days to weeks to form a large, annular erythematous lesion that ranges from 5 to 70 cm in diameter (median, 15 cm). This rash may be uniformly erythematous, or it may appear as a target lesion with a variable degree of central clearing or central purpura (target lesion). It can vary greatly in shape and, occasionally, may have vesicular or necrotic areas in the center. Erythema migrans is usually asymptomatic but may be pruritic or painful, and it may be accompanied by systemic findings, such as fever, malaise, headache, regional lymphadenopathy, stiff neck, myalgia, or arthralgia. In a large prospective study of erythema migrans in adults, the erythema migrans rashes included homogenous erythema (59%), central erythema (30%), central clearing (9%), or central purpura (2%). In addition, 7% of lesions had central vesicles or ulcerations. Thus target lesions occurred in 41% of patients.

The most common manifestation of early disseminated Lyme disease in the United States is multiple erythema migrans. The secondary skin lesions, which usually appear 3 to 5 weeks after the tick bite, consist of multiple annular erythematous lesions similar to, but usually smaller than, the primary lesion. Other common manifestations of early disseminated Lyme disease are cranial nerve palsies, especially facial nerve palsy, and meningitis. Systemic symptoms such as fever, myalgia, arthralgia, headache, and fatigue also are common in this stage of Lyme disease. Carditis, which usually is manifested by third-degree heart block and/or myocarditis, is a rare manifestation of early disseminated disease.

The most common manifestation of late Lyme disease, which occurs weeks to months after the initial infection, is arthritis. The arthritis is usually monarticular and affects the large joints, particularly the knee. The affected joint often is swollen and mildly tender; the intense pain associated with a septic arthritis usually is not present. Encephalitis, encephalopathy, and polyneuropathy also are manifestations of late Lyme disease, but each is very rare.

The clinical manifestations of Lyme disease also may depend on which subspecies of B. burgdorferi is causing the infection. The differences in subspecies found in Europe and in North America may account for differences in the frequencies of certain clinical manifestations of Lyme disease in these areas. Neurologic manifestations of Lyme disease are more common in Europe, whereas rheumatologic manifestations are more common in North America. In addition, certain skin and soft tissue manifestations of Lyme disease, such as acrodermatitis chronica atrophicans and lymphocytomas, occur in Europe but are extremely rare in the United States.

There has been substantial controversy about an entity that has been called “chronic Lyme disease.” There is no evidence that persistent B. burgdorferi infection unresponsive to an appropriate antibiotic exists. Nonspecific symptoms (e.g., fatigue, irritability, forgetfulness, arthralgia, or myalgia) may persist for weeks or months in patients who are successfully treated for early Lyme disease; the presence of these subjective symptoms should not be regarded as an indication for additional antimicrobial therapy. These symptoms may respond to nonsteroidal antiinflammatory drugs. Within 6 months of completion of the initial course of antimicrobial therapy, these nonspecific symptoms usually resolve with or without any therapies. For the unusual patients who have symptoms that persist longer than 6 months after the completion of antimicrobial therapy, an attempt should be made to determine if there exists a non–Lyme disease explanation or if there has been reinfection. Most likely these are post–Lyme disease symptoms and the cause is unknown. A parallel example is persistent fatigue after mononucleosis, which was initially thought to be secondary to persistent Epstein-Barr virus (EBV) infection (and was called chronic mononucleosis). Later it was shown that the EBV viremia had resolved in these patients, and the cause of the persistent fatigue was unknown.

There is a network of doctors that diagnose many patients with “chronic Lyme disease,” including patients from non–Lyme endemic areas. Many of these patients diagnosed with “chronic Lyme disease” have no evidence of either current or past infection with B. burgdorferi . There have been four double-blind randomized clinical trials of long-term antibiotic treatment for patients with evidence of past infection with B. burgdorferi and subsequent symptoms that persist for at least 6 months after conventional (or longer) treatment with antibiotics. The results of all of these studies showed that long-term treatment provided little or no benefit but was associated with substantial risks to the patient. In addition, prolonged use of antibiotics encourages selection of antibiotic-resistant bacteria that pose risks to the patients and to the community. These results add to the already substantial data that “chronic Lyme disease” is not a persistent infection but more likely should be classified as a syndrome of medically unexplained symptoms or post–Lyme disease symptoms.

Ixodes ticks may transmit other pathogens in addition to B. burgdorferi, including Babesia, Anaplasma, other Borrelia species, and viruses. These agents may be transmitted either separately from or simultaneously with B. burgdorferi . The frequency with which coinfection occurs is unknown. The impact of coinfection on the clinical presentation and the response to treatment of Lyme disease, although well documented and important in rare selected cases, seems to be of minor significance in most instances. In the south-central United States, in areas such as Missouri, another tick-borne infection that causes erythema migrans has been recognized. Southern tick-associated rash illness (STARI) is transmitted by the tick Amblyomma americanum, the Lone Star tick. The cause of STARI was originally thought to be Borrelia lonestari, but this has not been confirmed. In contrast to Lyme disease, it does not seem to cause systemic disease. Similar to Lyme disease, there is no evidence that STARI is associated with congenital disease in children. STARI causes a rash similar to erythema migrans and in areas where the deer tick and Lone Star tick cohabitate, the skin manifestations of these two diseases overlap.

Diagnosis

The CDC clinical case definition for Lyme disease initially was intended for epidemiologic surveillance purposes. When used in conjunction with CDC and U.S. Food and Drug Administration (FDA) guidelines for diagnostic tests, however, this case definition has been widely accepted as a means to standardize the clinical diagnosis of Lyme disease ( Box 17-1 ).

For patients in locations endemic for Lyme disease who present with the characteristic lesion of erythema migrans, the diagnosis of Lyme disease should be based on the clinical presentation alone. In such situations, laboratory testing is neither necessary nor recommended. With the exception of erythema migrans, however, the clinical manifestations of Lyme disease are nonspecific. For patients who do not have erythema migrans, the diagnosis of Lyme disease should usually be based on objective clinical findings and positive laboratory tests. These laboratory tests may consist of either direct identification of B. burgdorferi in the patient or demonstration of a serologic response to the organism.

Methods for identifying the presence of B. burgdorferi in a patient (e.g., culture, histopathologic examination, antigen detection) generally have poor sensitivity or specificity or both and may require invasive procedures (e.g., a biopsy of the skin) to obtain an appropriate specimen for testing. Isolation of B. burgdorferi from a symptomatic patient should be considered diagnostic of Lyme disease. B. burgdorferi has been isolated from blood, skin biopsy specimens, cerebrospinal fluid (CSF), myocardial biopsy specimens, and the synovium of patients with Lyme disease. B. burgdorferi can take 6 weeks to grow in culture. The best chance of culturing B. burgdorferi from a patient is when erythema migrans is present, although at this stage of the disease, the diagnosis should be largely clinical. During the later stages of Lyme disease, culture is much less sensitive. In addition, it is necessary for patients to undergo an invasive procedure, such as a biopsy, to obtain appropriate tissue or fluid for culture. Culture is indicated only in rare circumstances.

B. burgdorferi has been identified with silver stains (Warthin-Starry or modified Dieterle) and with immunohistochemical stains (with monoclonal or polyclonal antibodies) in skin, synovial, and myocardial biopsy specimens. B. burgdorferi can be confused with normal tissue structures, however, or it may be missed because it often is present in low concentrations. Considerable training and experience are needed for skill in identifying spirochetes in tissues. Direct detection of B. burgdorferi in tissue is of limited practical value.

Attempts have been made to develop antigen-based diagnostic tests for Lyme disease, but no convincing data indicating the accuracy of any of these tests are available. All of these tests should be considered experimental until additional studies confirm their validity and reproducibility. Assays to detect B. burgdorferi antigens in CSF or urine have poor specificity and poor sensitivity and are not recommended.

Tests that use PCR techniques to identify B. burgdorferi are sometimes helpful. Results of such tests may be positive for some time after the spirochetes are no longer viable, however. In addition, the risk of false-positive results on PCR assays is great, especially when they are performed in commercial laboratories. If a PCR test is done, it should be performed in a reference laboratory that meets the highest standards of quality control for diagnostic PCR assays. Because of its limited availability, expense, and insufficient evidence of its value in the management of most patients, PCR is at present reserved for special situations. Use of PCR assay may be appropriate in testing of specimens such as synovial tissue or fluid from patients with persistent arthritis after a course of appropriate antibiotic therapy for late Lyme disease; samples of abnormal CSF from patients who are seropositive for antibodies to B. burgdorferi and have a neurologic illness that is compatible with, but not typical of, Lyme disease. At present, there is insufficient evidence of the accuracy, predictive value, or clinical significance of a PCR test of urine for B. burgdorferi, and its use for decisions regarding the management of patients has been strongly discouraged.

In most cases, the confirmation of Lyme disease in patients without erythema migrans usually is based on the demonstration of antibodies to B. burgdorferi in the serum. The normal antibody response to acute infection with B. burgdorferi is well described. Specific IgM antibodies appear first, usually 3 to 4 weeks after the infection begins. These antibodies peak after 6 to 8 weeks and usually decline. A prolonged elevation of IgM antibodies sometimes is seen, however, even after effective antimicrobial treatment. Consequently, the results of serologic tests for specific IgM antibodies should not be used as the sole indicator of the timing of an infection. Specific IgG antibodies usually appear 6 to 8 weeks after the onset of the infection. These antibodies peak in 4 to 6 months. The IgG antibody titer may decline after treatment, but even after the patient is clinically cured, these antibodies usually remain detectable for many years.

The immunofluorescent antibody test was the initial serologic test for diagnosing Lyme disease. It requires subjective interpretation and is time consuming to perform. It has largely been replaced by the ELISA. The ELISA method may give false-positive results because of cross-reactive antibodies in patients with other spirochetal infections (e.g., syphilis, leptospirosis, relapsing fever), certain viral infections (e.g., varicella), and autoimmune diseases (e.g., systemic lupus erythematosus). In contrast to patients with syphilis, patients with Lyme disease do not have positive results on nontreponemal tests for syphilis, such as the Venereal Disease Research Laboratory or rapid plasma reagin (RPR). In addition, antibodies directed against bacteria in the normal oral flora may cross react with antigens of B. burgdorferi to produce a false-positive ELISA result.

The first-generation ELISA method used either whole cells of B. burgdorferi or the supernatant of sonicated spirochetes as the antigen. To improve the specificity of the ELISA, new assays have been developed that use less complex fractions of the spirochetes, such as the bacterial membrane, or purified native or recombinant proteins, alone or in combination.

Immunoblot (western blot) analysis for serum antibodies to B. burgdorferi also is used as a serologic test for Lyme disease. Some investigators have suggested that immunoblot is more sensitive and more specific than ELISA, but this is debatable. Immunoblot is most useful for validating a positive or equivocal ELISA result, especially in patients with a low clinical likelihood of having Lyme disease. For serologic testing for Lyme disease, it is recommended that a sensitive ELISA be performed, and, if results are either positive or equivocal, that a western blot analysis be done to confirm the specificity of the result. Specimens that give a negative result on a sensitive ELISA do not require immunoblot.

One reason for the poor sensitivity of serologic tests for Lyme disease is that erythema migrans, which is the clinical finding that usually brings patients to medical attention, usually appears within 2 to 3 weeks of onset of infection with B. burgdorferi . Antibodies to B. burgdorferi often are not detected at this early stage of the disease. The antibody response to B. burgdorferi also may be abrogated in patients with early Lyme disease who receive prompt treatment with an effective antimicrobial agent; in these patients, antibodies against B. burgdorferi may never develop, at least as a result of that exposure. Most patients with early, disseminated Lyme disease and virtually all patients with late Lyme disease have serum antibodies to B. burgdorferi, however. Seropositivity may persist for years, even after successful antimicrobial therapy. Ongoing seropositivity, even persistence of IgM, is not a marker of active infection. Likewise, serologic tests should not be used to assess the adequacy of antimicrobial therapy.

Serologic tests for Lyme disease have not been adequately standardized. The accuracy and the reproducibility of currently available serologic tests, especially widely used, commercially produced kits, are poor. Use of these commercial diagnostic test kits for Lyme disease would result in a high rate of misdiagnosis. As with any diagnostic test, the predictive value of serologic tests for Lyme disease depends primarily on the probability that the patient has Lyme disease based on the clinical and epidemiologic history and the physical examination (the “pretest probability” of Lyme disease). Use of serologic tests to “rule out” Lyme disease in patients with a low probability of the illness would result in a very high proportion of test results that are falsely positive. Antibody tests for Lyme disease should not be used as screening tests.

With few exceptions, the probability that a patient has Lyme disease would be very low in areas in which Lyme disease is rare. Even in areas with a high prevalence of Lyme disease, patients with only nonspecific signs and symptoms, such as fatigue, headache, and arthralgia, are not likely to have Lyme disease. Although such nonspecific symptoms are common in patients with Lyme disease, they are almost always accompanied by more specific objective findings, such as erythema migrans, facial nerve palsy, or arthritis. Even when more accurate tests performed by reference laboratories are available, clinicians should order serologic tests for Lyme disease selectively, reserving them for patients from populations with a relatively high prevalence of Lyme disease who have specific objective clinical findings that are suggestive of Lyme disease so that the predictive value of a positive result is high.

If a symptomatic patient is positive for antibodies to B. burgdorferi, Lyme disease may or may not be the cause of that patient’s symptoms. The positive test may be a false-positive result (a common occurrence), or the patient may have been infected with B. burgdorferi previously. When serum antibodies to B. burgdorferi do develop, they may persist for many years despite adequate treatment and clinical cure of the illness. In addition, there is a background rate of seropositivity among patients in endemic areas who have never had clinically apparent Lyme disease.

The diagnosis of an infection of the central nervous system (CNS) with B. burgdorferi is made by showing the presence of inflammation in the CSF and Borrelia -specific intrathecal antibodies. Most patients with typical cases of Lyme neuroborreliosis have antibodies to B. burgdorferi in serum, and testing for the presence of antibodies in the CSF usually is unnecessary. In some instances, examination of the CSF for antibodies to B. burgdorferi may be indicated. Because antibodies to B. burgdorferi may be present in the CSF as the result of passive transit through a leaky blood-brain barrier, detection of antibodies in the CSF is not proof of infection. Better evidence of CNS disease is the demonstration of intrathecal production of antibodies. This can be accomplished by simultaneously measuring the antibodies in the serum and CSF by ELISA and calculating the “CSF index.” PCR assay of the CSF is usually not helpful because of low sensitivity for confirming the diagnosis of CNS Lyme disease.

A lymphoproliferative assay that assesses the cell-mediated immune response to B. burgdorferi has been developed as a diagnostic test for Lyme disease. This assay has not been standardized, however, and is not approved by the FDA. The indications for this lymphoproliferative assay are few, if any.

The diagnosis of Lyme disease in a pregnant woman should be made in accordance with the currently accepted CDC case definition (see Box 17-1 ). There is no indication for routine prenatal serologic screening of asymptomatic healthy women. Serosurveys have shown that the seroprevalence rates among pregnant women were comparable to those in the general population and that asymptomatic seroconversion during pregnancy was unusual.