Lyme Disease

Introduction: Lyme disease was named in 1977 when arthritis was observed in a cluster of children in and around Lyme, Connecticut. Other clinical symptoms and environmental conditions suggested that this was an infectious disease probably transmitted by an arthropod. Further investigation revealed that Lyme disease is caused by the bacterium, Borrelia burgdorferi. These bacteria are transmitted to humans by the bite of infected deer ticks and cause more than 16,000 infections in the United States each year.

            Vector: Black-legged ticks (Ixodes scapularis) are responsible for transmitting Lyme disease bacteria to humans in the northeastern and north-central United States. On the Pacific Coast, the bacteria are transmitted to humans by the western black-legged tick (Ixodes pacificus). Ixodes ticks are much smaller than common dog and cattle ticks. In their larval and nymphal stages, they are no bigger than a pinhead. Ticks feed by inserting their mouths into the skin of a host and slowly take in blood. Ixodes ticks are most likely to transmit infection after feeding for two or more days.

Risk: In the United States, Lyme disease is mostly localized to states in the northeastern, mid-Atlantic, and upper north-central regions, and to several counties in northwestern California. In 1999, 16,273 cases of Lyme disease were reported to the Centers for Disease Control and Prevention (CDC). Ninety-two percent of these were from the states of Connecticut, Rhode Island, New York, Pennsylvania, Delaware, New Jersey, Maryland, Massachusetts, and Wisconsin.

Individuals who live or work in residential areas surrounded by tick-infested woods or overgrown brush are at risk of getting Lyme disease. Persons who work or play in their yard, participate in recreational activities away from home such as hiking, camping, fishing and hunting, or engage in outdoor occupations, such as landscaping, brush clearing, forestry, and wildlife and parks management in endemic areas may also be at risk of getting Lyme disease.

Prevention and Treatment: It is important to remember that prevention measures can be effective in reducing your exposure to infected ticks. Avoid tick habitats: Whenever possible, avoid entering areas that are likely to be infested with ticks, particularly in spring and summer when nymphal ticks feed. Ticks favor a moist, shaded environment, especially areas with leaf litter and low-lying vegetation in wooded, brushy or overgrown grassy habitat. Both deer and rodent hosts must be abundant to maintain the enzootic cycle of B. burgdorferi.

Use personal protection measures:
Wear light-colored clothing so that ticks can be spotted more easily and removed before becoming attached. Wearing long-sleeved shirts and tucking pants into socks or boot tops may help keep ticks from reaching your skin. Ticks are usually located close to the ground, so wearing high rubber boots may provide additional protection.

Use of insect repellents containing DEET (n,n-diethyl-m toluamide) to clothes and exposed skin, and applying permethrin (which kills ticks on contact) to clothes.

Perform a tick check and remove attached ticks: The transmission of B. burgdorferi (the bacteria that causes Lyme disease) from an infected tick is unlikely to occur before 36 hours of tick attachment. For this reason, daily checks for ticks and promptly removing any attached tick that you find will help prevent infection. Embedded ticks should be removed using fine-tipped tweezers. DO NOT use petroleum jelly, a hot match, nail polish, or other products. Grasp the tick firmly and as closely to the skin as possible. With a steady motion, pull the tick's body away from the skin. The tick's mouthparts may remain in the skin, but do not be alarmed. The bacteria that cause Lyme disease are contained in the tick's midgut or salivary glands. Cleanse the area with an antiseptic.

Taking preventive antibiotics after a tick bite: In most circumstances, treating persons who only have a tick bite is not recommended. Individuals who are bitten by a deer tick should remove the tick promptly, and may wish to consult with their health care provider. Persons should promptly seek medical attention if they develop any signs and symptoms of early Lyme disease,

Strategies to reduce tick abundance: Such as deer feeding stations equipped with pesticide applicators to kill ticks on deer, and baited devices to kill ticks on rodents, are currently under evaluation.

Lyme disease vaccine: As of February 25, 2002 the manufacturer announced that the LYMErix™ Lyme disease vaccine is  no longer be commercially available

Diagnosis

Clinical Description:

Early Localized Infection  First symptom: "bull's-eye" rash, erythema migrans, The incubation period from infection to onset of erythema migrans is typically 7 to 14 days followed in 50% of cases by fever, malaise, fatigue, headache, myalgia and arthralgia. Some infected individuals have no recognized illness

Early Disseminated: Days to weeks after the appearance of a solitary erythema migrans lesion other symptoms involving  the nervous system, the musculoskeletal system, or the heart can appear.

• Early neurologic manifestations include lymphocytic meningitis, cranial neuropathy (especially facial nerve palsy), and radiculoneuritis.
• Musculoskeletal manifestations may include migratory joint and muscle pains with or without objective signs of joint swelling.
• Cardiac manifestations are rare but may include myocarditis and transient atrioventricular blocks of varying degree.

Late disseminated disease weeks to months after untreated  infection.

• Intermittent swelling and pain of one or a few joints, usually large, weight-bearing joints such as the knee.
• Polyneuropathy, or encephalopathy, the latter usually manifested by cognitive disorders, sleep disturbance, fatigue, and personality changes. Infrequently, Lyme disease morbidity may be severe, chronic, and disabling. Lyme disease is rarely, if ever, fatal.

Diagnosis:

• The diagnosis of Lyme disease is based primarily on clinical findings, and it is often appropriate to treat patients with early disease solely on the basis of objective signs and a known exposure.
• Serologic testing may, however, provide valuable supportive diagnostic information in patients with endemic exposure and objective clinical findings that suggest later stage disseminated Lyme disease. When serologic testing is indicated, CDC recommends testing initially with a sensitive first test, either an enzyme-linked immunosorbent assay (ELISA) or an indirect fluorescent antibody (IFA) test, followed by testing with the more specific Western immunoblot (WB) test to corroborate equivocal or positive results obtained with the first test.

Treatment:

Antibiotic treatment for 3-4 weeks with doxycycline or amoxicillin is generally effective in early disease. Cefuroxime l or erythromycin can be used for persons allergic to penicillin or who cannot take tetracyclines.

 Later disease, particularly with objective neurologic manifestations, may require treatment with intravenous ceftriaxone or penicillin for 4 weeks or more, depending on disease severity. In later disease, treatment failures may occur and retreatment may be necessary.