Lyme Disease Is on the Rise

Lyme disease is caused by infection with a bacterium called a spirochete (Borrelia burgdorferi) and is transmitted to humans by infected ticks (Ixodes scapularis and I. Pacificus). Lyme disease is the most common vector-borne disease in the U.S. Patients with early stage Lyme disease have a characteristic rash (erythema migrans) accompanied by nonspecific symptoms (for example, fever, malaise, fatigue, headache, myalgia, and arthralgia). Lyme disease can usually be treated successfully with standard antibiotics.

The U.S. Centers for Disease Control and Prevention (CDC) reports that over 30,000 Americans were diagnosed with Lyme disease in 2014, representing more than a 30% increase in the annual rate in the past decade. It is suggested that the increase in reported cases is probably a result of both a true increase in incidence within known high-risk areas as well as more complete reporting as a result of enhanced Lyme disease surveillance. They noted that surveillance capabilities and public awareness of Lyme disease have increased during this period. Additionally, there has been an increase in the number of clinically diagnosed cases of Lyme disease that are not substantiated by laboratory testing.

Researchers also note that Lyme disease remains underreported with an estimated seven to 12 cases for each reported case.

Geographic and seasonal patterns of disease correlate with the distribution and feeding habits of the vector ticks. Most cases of Lyme disease occur in states that are known to be high risk. A total of 92% of cases was reported from eight northeastern and mid-Atlantic states and two north-central states. Less than 8% of cases were reported from states with low or no known risk for Lyme disease. The majority of reported cases had onsets of disease in June, July, or August -- the months when humans most commonly engage in outdoor activities. Researchers believe that a majority of human cases result from young ticks. Because the attached young tick (nymph) is approximately the size of a poppy seed, it might not be noticed and, therefore, not removed before disease transmission occurs. It has been suggested that factors contributing to the rise in reported cases of Lyme disease include proliferation of the animal hosts of the ticks and Lyme bacterium, including rodents and deer, as well as warmer weather during the season of tick reproduction during the summertime.

Children 5-10 years of age and adults 35-54 years of age are most commonly affected. The risk of Lyme disease increases with increasing exposure to wooded, brushy, or overgrown grassy areas in high-risk states. States reporting the highest incidence of Lyme disease in the study were New York, Connecticut, Pennsylvania, New Jersey, Wisconsin, Rhode Island, Maryland, Massachusetts, Minnesota, and Delaware.

Prevention and educational programs in endemic areas have stressed the use of personal protective measures. Wearing long clothing can protect the skin. Clothing, children, and pets should be examined for ticks. Ticks can be removed gently with tweezers and saved in a jar for later identification. Bathing the skin and scalp and washing clothing upon returning home might prevent the bite and transmission of the disease. Other prevention strategies attempt to reduce the density of I. scapularis in the environment and include deer exclusion or removal, application of acaricides or desiccants to vegetation, landscape management (for example, removal of leaf litter), host-targeted acaricides, and the use of vaccine (none currently available). To make the most efficient use of limited resources, prevention strategies should consider the geographic and temporal distribution of Lyme disease risk and appropriately target communities at moderate and higher risk.