Lyme Disease

Brief Description:

Lyme disease, or borreliosis, is an emerging infectious disease caused by bacteria from the genus Borrelia. The vector of infection is typically the bite of an infected black-legged or deer tick, but other carriers (including other ticks in the genus Ixodes) have been implicated.

Signs & Symptoms:

The acute phase of Lyme disease infection is a characteristic reddish "bulls-eye" rash, with accompanying fever, malaise, and musculoskeletal pain (arthralgia or myalgia). The characteristic reddish "bull's-eye" rash (known as erythema chronicum migrans) may be seen in up to 80% of early stage Lyme disease patients, appearing anywhere from one day to a month after a tick bite. The rash does not represent an allergic reaction to the bite, but a skin infection cause by the Lyme bacteria. The incubation period from infection to the onset of symptoms is usually 1–2 weeks, but can be much shorter (days), or much longer (months to years). Symptoms most often occur from May through September because the nymphal stage of the tick is responsible for most cases.

Causes:

Lyme disease is caused by Gram-negative spirochetal bacteria from the genus Borrelia. At least 37 Borrelia species have been described, 12 of which are Lyme related. Hard-bodied ticks of the genus Ixodes are the primary vectors of Lyme disease. The majority of infections are caused by ticks in the nymph stage, as adult ticks are more easily detected and removed as a consequence of their relatively large size.

Diagnosis:
Due to the difficulty in culturing Borrelia bacteria in the laboratory, diagnosis of Lyme disease is typically based on the clinical exam findings and a history of exposure to endemic Lyme areas.

Treatment:

Antibiotics are the primary treatment for Lyme disease. Penicillin was first demonstrated by researchers to be useful against Borrellia in the 1950s; today the antibiotics of choice are doxycycline, amoxicillin and ceftriaxone. Macrolide antibiotics are also used.

Prevention:

Stay away from ticks.

Epidemiology:

Lyme disease is the most common tick-borne disease in North America and Europe, and one of the fastest-growing infectious diseases in the United States. Of cases reported to the United States Center for Disease Control (CDC), the ratio of Lyme disease infection is 7.9 cases for every 100,000 persons. In the ten states where Lyme disease is most common, the average was 31.6 cases for every 100,000 persons for the year 2005.