I. LYME DISEASE (Lyme borreliosis) is the most commonly reported vectorborne disease in the United States. The causative organism is the spirochete Borrelia burgdorferi sensu stricto, which is transmitted to humans through the bite of the Ixodes tick. In the United States, the cases of Lyme disease correlate with the distribution of the infected tick vector: Ixodes scapularis in the East and Midwest and Ixodes pacificus in the West. Most cases in the United States are clustered in the northeast New England states but extend down the Atlantic coast to Virginia, in the Midwest in Wisconsin and Minnesota, or with less frequency in the west in northern California. Lyme disease also occurs in eastern Canada, Europe, China, Japan, and Russia. In Eurasia, there are two additional genotypes (Borrelia afzelii and Borrelia garinii) that cause Lyme disease but with a variation in the clinical presentation. In the United States, humans are most likely to be infected in the summer months of June through August. The incubation period from tick bite to the appearance of skin lesion(s) ranges from 1 to 32 days with a median of 11 days.

The clinical manifestations of Lyme disease are generally divided into three stages: early localized, early disseminated, and late disease. In the early localized stage, an annular, erythematous, nonpruritic lesion known as erythema migrans presents at the site of a tick bite, usually within 1 to 2 weeks. Over several days, the lesion enlarges to 5 cm or more in diameter and occasionally develops central clearing providing the classic “bulls-eye” appearance. The early localized stage may present with or without constitutional symptoms such as malaise, headache, neck stiffness, myalgia, and arthralgia. Patients with early disseminated disease commonly present with multiple erythema migrans lesions due to spirochetemia, weeks to months after the initial tick bite. These lesions are typically smaller than the primary solitary lesion seen in early localized disease. Other manifestations of early disseminated disease may include neurologic involvement (lymphocytic meningitis, cranial nerve palsy—especially cranial nerve VII—and peripheral radiculopathy), carditis (atrioventricular block
and myocardial dysfunction), and ocular manifestations (conjunctivitis, optic neuritis, keratitis, and uveitis). Patients may also have mild constitutional symptoms during this stage. Late disseminated disease occurs months to years after the onset of infection, typically in a patient without a history of early localized or early disseminated Lyme disease. The most common manifestation is recurrent pauciarticular arthritis of large joints with few cases presenting with encephalopathy, encephalitis, or polyneuropathy.

Early case reports and case series have documented that transplacental transmission of B. burgdorferi was possible and raised concerns about a potential congenital Lyme disease syndrome analogous to that seen with other spirochetal infections such as syphilis. A wide variety of clinical manifestations were noted, with most initial concerns being focused on congenital cardiac malformations and fetal death. However, epidemiologic studies and literature reviews have not supported an association between congenital infection and adverse fetal or neonatal outcomes. A prospective study of 2,014 pregnant women living in an endemic area had Lyme serology during their first prenatal visit and at delivery. Results showed no association between seropositivity or history of tick bite during pregnancy and congenital malformations, low birth weight, premature delivery, or fetal death. A report by the same authors compared 2,504 infants born in an endemic region to 2,507 delivered in a nonendemic region. This study showed a significant increase in the rate of congenital cardiac malformations in the endemic compared with the nonendemic region, but notably, no association within the endemic region between seropositivity and cardiac malformation. Similarly, in a retrospective case control study of 796 children with congenital heart disease and 704 control children, there was no association between cardiac anomalies and clinical evidence of Lyme disease during pregnancy. Although these studies were limited by the low prevalence of Lyme disease, it appears from available evidence that any increased risk for adverse neonatal effects of prenatal Lyme borreliosis are likely to be small.