Lyme Disease, 2015

Lyme disease is caused by Borrelia burgdorferi, a spirochete transmitted to humans by bites from Ixodes scapularis (the blacklegged tick or deer tick) in Minnesota. Recently, a new species of bacteria, Borrelia mayonii, has also been identified as a cause of human disease. In Minnesota, the same tick vector also transmits the agents of babesiosis, Anaplasmosis, one form of human ehrlichiosis, and a strain of Powassan virus.

In 2015, 1,176 confirmed Lyme disease cases (20.7 cases per 100,000 population) were reported (Figure 1). In addition, 630 probable cases (physician-diagnosed cases that did not meet clinical evidence criteria for a confirmed case but that had laboratory evidence of infection) were reported. Despite some yearly fluctuations, the number of reported cases of Lyme disease has been increasing, as evidenced by the median number of cases from 2006 through 2015 (median, 1,121; range, 896 to 1,431) compared to the median from 1996 to 2005 (median, 464; range, 252 to1,023).

Seven hundred forty (63%) confirmed cases in 2015 were male. The median age was 44 years (range, 1 to 91 years). Physician-diagnosed erythema migrans (EM) was present in 882 (75%) cases. Three hundred thirty-four (28%) cases had one or more late manifestations of Lyme disease (including 218 with a history of objective joint swelling, 95 with cranial neuritis, including Bell’s palsy, 9 with lymphocytic meningitis, 14 with acute onset of 2nd or 3rd degree atrioventricular conduction defects, and 8 with radiculoneuropathy) and confirmation by Western immunoblot (positive IgM ≤30 days post-onset or positive IgG). In 2015, 1 death due to Lyme disease was reported. The patient, a 59 year-old male, was diagnosed with Lyme carditis post-mortem. Of the 1,105 cases with known onset dates, onset of symptoms peaked from June through August, with 43% of EM cases experiencing symptom onset in July. This timing corresponds with peak activity of nymphal I. scapularis ticks in mid-May through mid-July. The majority of cases in 2015 either resided in or traveled to endemic counties in north-central, east-central, or southeast Minnesota, or Wisconsin.

• For up to date information see: Lyme disease
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2015