MEDICAL DIAGNOSTIC LABORATORIES, L.L.C. Lyme Disease INTRODUCTION EPIDEMIOLOGY Early in the 20th century, European physicians observed Lyme disease (LD), caused by infection with Borrelia patients with a red, slowly expanding rash called erythema burgdorferi, is the most common vector-borne disease in the migrans (EM) (Figure 1) (1). They associated this rash with United States, accounting for more than 95% of all reported the bite of ticks and postulated that EM was caused by a tick- vector-borne illnesses. From 2003-2005, 64,382 cases of borne bacterium. In the 1940s, a similar tick-borne illness Lyme disease were reported to the CDC from 46 states and was described that often began with EM and developed into the District of Columbia (2). However, a considerable level a multi-system illness. In 1969, a physician in Wisconsin of underreporting is associated with Lyme Disease and, diagnosed a patient with EM and successfully treated the therefore, the true number of infected individuals is probably individual with penicillin. In 1975, a women in Old Lyme, greater. Of the reported cases, 59,770 occurred within ten Connecticut contacted the state health authorities to ask why endemic states: Connecticut, Delaware, Maine, Maryland, so many children in her town had arthritis. She was alarmed Minnesota, New Jersey, New York, Pennsylvania, Rhode by the fact that 12 cases of juvenile arthritis, a relatively rare Island and Wisconsin (2). Within these endemic states, disease, had been diagnosed in a town with a population of the average annual rate of infection over this three year only 5,000. Subsequent investigations of these and similar period was 29.2 cases per 100,000 population (2). Three cases led to the discovery of Lyme disease and to the counties, New York’s Columbia and Dutchess counties and identification of the causative bacterium. Massachusetts’ Dukes County, were determined to have an incidence rate of 300 cases per 100,000 population (2). Evaluation of race and sex revealed a slightly higher incidence for males (54% of reported cases) and that 97% of the cases affect caucasians (2). Persons of all ages and both genders are equally susceptible, although the highest incidence of LD occurs in children ages 0-14 years and in persons 30 years of age and older (median, 28 years). LD has been reported in 49 states and the District of Columbia. Lyme borreliosis also occurs in temperate regions of the Northern Hemisphere in Europe (3), Scandinavia (4), the former Soviet Union (5), China (6) and Japan (7). In the United States, the infection is spreading and has caused focal epidemics, particularly in the northeastern United States (8-10). From 1985 to 1989, Figure 1: Erythema migrans rash in Lyme borreliosis. the number of counties in New York State with documented I. scapularis ticks increased from 4 to 22, and the number of In 1982, spirochetes were identified in the midgut of the counties endemic to LD increased from 4 to 8 (11). During black-legged, adult deer tick, Ixodes scapularis, and given the subsequent 10 years, I. scapularis ticks have spread to the name Borrelia burgdorferi. Finally, conclusive evidence 54 of the 62 counties in the state. In the US, the majority that B. burgdorferi caused Lyme disease came in 1984 when of affected individuals have had symptoms of the illness, spirochetes were cultured from the blood of patients with the whereas in Europe, the majority is asymptomatic (10, 11). rash EM and from the cerebrospinal fluid of a patient with Of 346 people who were studied in the highly endemic area meningoencephalitis and history of prior EM. The Centers for of Liso, Sweden, 41 (12%) had symptoms of the illness and Disease Control and Prevention (CDC) began surveillance 89 (26%) had evidence of subclinical infection (12). In a for Lyme disease in 1982. The Council of State and Territorial serosurvey of 950 Swiss orienteers, 26% had detectable IgG Epidemiologists (CSTE) designated Lyme disease as a antibodies to B. burgdorferi, but only 2% to 3% had a past nationally notifiable disease in January 1991. history of definite or probable LD (Figure 2) (1,13). www.mdlab.com • 877 269 0090 (C) Adult female black-legged or deer tick (I. scapularis). As a member of the greater I. persulcatus group that also includes I. pacificus, I. ricinus, and I persulcatus, this tick is an important vector of several infectious agents that cause disease in humans, including Lyme borreliosis, (granulocytic) anaplasmosis, Figure 2: Approximate geographic distributions of I. ovatus and babesiosis. I. persulcatus (green with horizontal lines), I. pacificus (red with horizontal lines), ticks elsewhere in the world I. persulcatus (red), I. ricinus (green), I. scapularis (blue), R. evertsi may also transmit tick-borne flaviviruses capable of causing (yellow with horizontal lines), and R. pumilio (yellow with vertical encephalitis, encephalomyelitis, and even hemorrhagic fevers lines). (including tick-borne encephalitis virus, louping ill virus, Russian spring-summer encephalitis virus, Powassan virus, Kyasanur Forest TICK BIOLOGY Disease virus, and Langat virus). Images courtesy of G. Maupin. Ticks evolved 94 million years ago from mites as parasites To accomplish a successful blood meal, a tick has to (i) attach of reptiles, birds, and mammals. More than 50 species of to the host, (ii) impair local itching and pain responses to stay ticks can feed on humans (13, 14). Ticks belong to two undetected, (iii) prepare the tissue for blood extraction, (iv) taxonomic families, the soft ticks (Argasidae) and the hard prevent blood clotting, and (v) suppress the local immune ticks (Ixodidae). Humans are not the principal, but rather the and inflammatory responses (16). serendipitous host for most ticks (Figure 3) (1). Figure 3: (A) Adult female Attachment: Upon finding a suitable host, the tick raises its lone star tick (Ameblyoma body at an angle to the skin surface and the chelicerae begin americanum). The lone star to cut the epidermis (17). Mouthpart lengths differ significantly, tick is broadly distributed throughout the southeastern with lengths in Dermacentor (dog ticks) extending to the quadrant of the United States, dermis-epidermis interface, while the mouthparts of Ixodes with ranges extending into New species extend well into the dermis (18). England and the Midwestern states. All three life cycle Cement: Salivary glands of Ixodid ticks generally secrete stages of A. americanum can an attachment cement, which is believed to serve as an bite humans. A. americanum adhesive and to seal the bite lesion bridging the cleft between is a recognized vector of mouthparts and host tissue (19). Attachment cement several pathogens that cause diseases in humans, including ehrlichioses caused by E. chaffeensis secretion begins within minutes after skin penetration and and E. ewingii, and has been implicated as a vector of southern tick- hardens into a tube surrounding the mouthparts. associated rash illness believed to be caused by Borrelia lonestari. Other pathogens or potential pathogens have also been detected Mechanics: Cutting action and mouthpart insertion produces in this tick, including various spotted fever group rickettsiae, an expanding hemorrhagic pool within the tissues, which is Francisella tularensis, and Coxiella burnetti, although the role of A. aided by anticoagulants, vasodilators, and platelet aggregation americanum in the transmission of these agents to humans is not inhibitors in tick saliva (17). Mouthpart mechanical actions well characterized. (B) Adult alone are not sufficient to account for the lesion. The lesion female American dog tick (Dermacentor variabilis). is characterized by a large blood-filled cavity. Ixodid tick This tick is abundant in the blood feeding is not continuous (17). The first few days of southeastern United States hard tick feeding are referred to as the slow feeding phase, and coastal New England, which coincides with cuticle growth to accommodate the with limited distribution in blood meal. Next, the rapid feeding phase is characterized several midwestern states, by the uptake of very large quantities of blood. The increase southern Canada, and in size during the 7 to 10 day slow-feeding phase can be western coastal regions. 10-fold, with an additional 10-fold increase during the rapid- The tick is best known as the primary vector of Rocky feeding phase (20). This increase actually underestimates Mountain spotted fever in the amount the blood consumed, since fluid from the blood the eastern United States. meal is reintroduced into the host during salivation (20). MOLECULAR AND BIOLOGICAL Pain and Itch: Pain and/or itching are important host responses that alert an individual to the presence of a ASPECTS OF FEEDING tick, resulting in grooming behavior that removes the tick. Ticks evolved strategies to overcome host hemostasis, pain Bradykinin is a peripheral mediator of the sensations of and itch responses, inflammation, and immune defenses itching (17) and pain (22). I. scapularis saliva contains a by secreting saliva, which contains a complex array of metallodipeptidyl carboxypeptidase capable of degrading pharmacologically active molecules (Figure 4) (1). active bradykinin (23). Bradykinin also has roles in inflammation and increases vascular permeability (24). Histamine is one of several mediators that transmit the sensation of itching through peripheral sensory nerve endings (17). In addition, a combination of histamine and serotonin, a further mediator of itching, inhibits tick feeding (25). Histamine binding proteins are produced by the salivary glands of many tick species like Rhipicephalus sanguineus A (26) and I. scapularis (27). Blood Coagulation and Tick Anticoagulants: Blood coagulation is a critical mechanism to prevent blood loss from the vasculature and poses a major obstacle for blood- feeding parasites, including ticks. Blood coagulation results B from activation of the extrinsic tissue factor and intrinsic pathways, which converge to form activated factor X (Xa) to initiate the common pathway of coagulation (28). Ticks have developed numerous redundant and complementary ways to inhibit coagulation.