Student presentation on
By: Marianne Tawadros
Wadsworth Center, New York State Dept. of Health
Lyme disease is an infection caused by Borrelia burgdorferi, a spirochete that is found in deer ticks of genus Ixodes. Lyme disease was named in 1977 after arthritis was observed in clusters in children in Lyme, Connecticut. An infected tick can transmit B. burgdorferi to the humans and animals that it bites. If left untreated, the B. burgdorferi can cause a systemic infection by traveling through the bloodstream and establishing itself in various body tissues. Lyme disease is most prevalently found in north-eastern United States.
Microbial Characteristics and Virulence:
Borrelia burgdorferi is not classified as either Gram-positive or Gram-negative. When B. burgdorferi is Gram-stained, the cells stain a weak Gram-negative by default, as safrin is the last dye used. B. burgdorferi has an outer membrane that contains an LPS-like substance, an inner membrane, and a periplasmic space which contains a layer of peptidoglycan. They have endoflagella which are contained within the periplasmic space. It can be cultivated on a modified Kelly medium called BSK (Barbour-Stoenner-Kelly). BSK solidified with 1.3% agarose allows the production of colonies from single organisms. The spirochete grows more slowly than most other bacteria dividing once after 12-24 hours. B. burgdorferi resembles other spirochetes in that it is a highly specialized, motile, two-membrane, spiral-shaped bacteria which lives primarily as an extracellular pathogen. One of the most striking features of B. burgdorferi as compared with other eubacteria is its unusual genome, which includes a linear chromosome approximately one megabase in size and numerous linear and circular plasmids. Long-term culture of B. burgdorferi results in a loss of some plasmids and changes in expressed protein profiles. Associated with the loss of plasmids is a loss in the ability of the organism to infect laboratory animals, suggesting that the plasmids encode key genes involved in virulence.
Lyme disease usually presents with a characteristic “bull’s eye rash”, erythema migrans, along with fever, fatigue, headache, muscle aches, and joint aches. The incubation period from infection to onset of the rash is typically 1-2 weeks. Some patients may be asymptomatic and present with only non-specific symptoms. B. burgdorferi disseminate from the site of the tick bite through the blood stream. There are three clinical stages of Lyme disease: 1) the Localized Early (Acute) Stage, 2) the Early Disseminated Stage and 3) the Late Stage. The acute stage is characterized by solid red or bull’s eye rash at the site of the bite, swelling of the lymph glands near the bite, generalized achiness and headache. The early disseminated stage is characterized by two or more rashes not at the site of the bite, migrating pains in joints/tendons, headache, stiff neck, facial paralysis, tingling or numbness in the extremities, multiple enlarged lymph glands, abnormal pulse, sore throat, changes in vision, fever of 100 to 102 F, and severe fatigue. The late stage is characterized by arthritis of one or two large joints, disabling neurological disorders, and numbness in the extremities.
Diagnosis and Treatment:
Diagnosis of Lyme disease should be made solely on clinical symptoms and the presence of a tick bite, and not blood tests, which can often give false results if performed in the first month after initial infection. Later on blood tests are considered more reliable.
Antibiotics such as doxycycline or amoxicillin are administered for 3-4 weeks early in the disease. Cefuroxime, axetil or erythromycin are used for those who are allergic to penicillin or who can not take tetracylines. In the late stage of the disease patients may require treatment with intravenous ceftriaxone or penicillin for 4 or more weeks depending on disease severity. Most cases of Lyme Disease that are treated with antibiotics after the first few weeks of initial infection almost always results in a full cure. Treatment that is begun after the first three weeks will also likely provide a cure, but the rate decreases after treatment is prolonged.
Prevention of infection of B. burgdorferi includes avoiding tick habitats such as brushy or overgrown grassy habitats especially in the spring and summer. When going into tick infested habitats wear light colored clothing so that ticks can be easily seen and removed. Wear long sleeve shirts and tuck pants into socks or boot tops. Wear rubber boots since ticks tend to be located closer to the ground.
Lyme disease can be found in the northeastern, mid-Atlantic and the upper central regions of the United States. Ninety-two percent cases came from Connecticut, New York, New Jersey, Rhode Island, Pennsylvania, Delaware Maryland, Massachusetts, and Wisconsin. Lyme disease accounts for approximately 16,000 infections in the United States per year. Since 1982 there have been over 145,000 cases reported to health authorities in the US. Lyme disease accounts for 95% of vector borne illness and the incidence rate is 5 per 100,000 although this number may be less than true cases due to underreporting. People of all ages and both genders are equally susceptible, although highest attack rates are in children ages 0-14 years and in persons 30 years of age or older.