Description

• An infection caused by Borrelia spirochetes, transmitted primarily by ixodid ticks
• Ixodes scapularis (deer ticks) in the Northeast and Great Lakes areas
• Ixodes pacificus in the West (black-legged ticks and Western black-legged ticks)

Epidemiology

In 2021, a total of 24,611 confirmed and probable cases of Lyme disease were reported to CDC. Approximately 476,000 people may get Lyme disease each year in the United States.

Incidence
High incidence U.S. states: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, and Wisconsin

Prevalence
Predominant age: most common in children ages 5 to 14 years and in adults aged 55 to 70 years of age

Etiology and Pathophysiology

• Average incubation period of 7 to 10 days after tick bite
• The 1st week of July is the peak week of onset for confirmed and probable cases.
• If a tick is infected, the chance of transmission increases with time attached: 0% at 24 hours, 12% at 48 hours, 79% at 72 hours, and 94% at 96 hours of attachment
• The primary animal reservoir is the white-footed mouse.
• Spirochetes multiply and spread within dermis, resulting in characteristic (erythema multiforme [EM]) rash. Hematogenous dissemination results in involvement of central nervous system (CNS), cardiovascular, or other organ stems.

Genetics
Human leukocyte antigen haplotype DR4 or DR2 increases susceptibility to prolonged arthritis.

Risk Factors

Lyme endemic area; ixodid ticks are common on deer; hunters at increased risk

General Prevention

• Wear appropriate clothing when outdoors in endemic areas during times of high tick activity. Clothing should cover the ankles and pretreat clothes, shoes, and tents with 0.5% permethrin.
• “Tick checks”: Examine the skin after outdoor activities.
• Remove ticks as soon as possible to limit transmission.
• To prevent of tick bites: N,N-diethyl-meta-toluamide (DEET), picaridin ethyl-3-(N-n-butyl-N-acetyl) aminopropionate (IR3535), oil of eucalyptus (OLE), p-menthane-3,8-diol (PMD), 2-undecanone
• Prophylactic treatment with 1 dose of 200 mg of doxycycline within 72 hours of a tick that has been attached for at least 36 hours is indicated in endemic areas; number needed to treat = 50

Commonly Associated Conditions

• Coinfection with other tick borne illness (e.g., babesiosis, ehrlichiosis, anaplasmosis)
• Comorbid human granulocytic anaplasmosis and/or babesiosis in patients living in endemic regions