Biology 2051

4 April, 2000

The causative organism of Lyme disease is identified primarily by three genomic groups; Borrelia burgdorferi, B. garinii, B. afzelii, all three of the species are classified as spirochaetes that are nuetrophilic fastidious aerobes and are Gram negative(-). The medium used to grow these strains of Borrelia is Barbour-Stoenner-Kelly (BSK) agar and it grows at 33 C.

Lyme disease is a tickborne, spirochetal, zoonotic disease that is characterized by distinctive skin lesions, systemic symptoms and neurologic, rheumatologic and cardiac involvement occuring in varying combinations over a period of months to years. The illness typically begins in the early summer, and the first manifestation in majority of patients appears as a red papule that expands slowly in an annular manner, sometimes with multiple similar lesions. Systemic manifestations may include malaise, fatigue, fever, headache, stiff neck, myalgia, and migratory arthralgias that could last several weeks or more in untreated patients. Within weeks to months after lesions have appeared neurologic abnormalities may develop, symptoms fluctuate and may last for months becoming chronic. Cardiac abnormalities may also begin to occur a few weeks after the onset of lesions. Weeks to years after the onset of the lesions swelling and pain in the larger joints especially the knees may develop and recur for several years. Diagnosis is currently based on clinical findings supported by serologic data by IFA, ELISA and immunoblotting techniques. Because of the sensitivity of the IFA tests patients with early symptoms as well as patients who have been treated early with antibiotics result with negative tests; therefore, the tests must be interpreted with caution. The ELISA for IgM antibodies has been shown to be more sensitive for early diagnosis. Test sensitivity increases when patients progress to later stages of the disaese, but small portions of chronic Lyme disease patients may remain seronegitive. Cross-reacting antibodies may cause a false positive test in patients with syphilis, relapsing fever, leptospirosis, HIV, Rocky Mountain spotted fever, and infectious mononucleosis.

Lyme disease is the number one tick transmitted disease in public health and is also the number one vector borne disease in the United States. Lyme disease accounts for about 90% of vector-borne infections in the U.S. and between 1980 and 1998 over 112,000 cases were reported from 49 states. The distribution of the majority of cases in the U.S. coincides with the distribution of the genus Ixodes tick. In the U.S. endemic foci exists along the Atlantic coast from Massachusetts to Maryland, in the upper midwest the expanding focus is currently concentrated in Wisconsin and Minnesota, and in the west in California and Oregon. The majority of recorded cases occur in the summer and it may be highly endemic. In some areas up to 4% of the population can be infected and ages 25-44 are most commonly infected. More than 50% of Ixodes ticks in the northeastern U.S. are infected with B. burgdorferi through transstadial transmission. In the northeastern and midwestern U.S., wild rodents and other animals maintain the enzootic transmission cycle. Deer serve as important maintenance mammalian hosts for vector tick species. Larval and nymphal ticks feed on small mammals and adult ticks feed primarily on deer. Transmission usually occurs by transmission of the ticks saliva to the host after the tick has been attached for twenty-four hours or more. There have also been recorded cases of dog owners becoming symptomatic after having crushed engorged ticks with their fingers through the mucus membrane. Nymphs are responsible for 90% of the cases transmitted by I. Dammini (deer tick) because 50-60% of the adults are infected, and rarely feed on humans; only 1% of the larvae are infected but they are not involved in the transmission to humans. There is no evidence of natural transmission from person to person; however, there are rare case reports of congenital transmission, but studies have not shown a link between maternal Lyme disease and adverse outcomes of pregnancy.

Prevention, treatment, and control involve relatively easy to follow and understand steps. Receintly human vaccinations have been developed, approved and made available. Education of the public in mode of transmission by ticks and avoiding tick infested areas when feasible is at the top of the list. If a person is working in an infested area, wear suitable clothing that covers the arms