History and Distribution
In 1975, two concerned mothers from Lyme, Connecticut reported a cluster of children thought to have juvenile rheumatoid arthritis. A surveillance system was created within the surrounding communities to identify children with inflammatory joint disease. A study was undertaken at Yale University to determine the cause, and 39 children were found with similar symptoms.
The studies showed that the cases were clustered, and that the infection rate among children was 12.2/1000, a frequency 100 times that of juvenile rheumatoid arthritis. Even within these clustered communities, there were even smaller clusters of disease incidence. Half of the affected Lyme residents lived in heavily wooded areas on two adjoining country roads, as did half of those affected in a nearby community. Clustering within the families was also observed with six families having more than one affected member. The majority of patients noted onset of symptoms in the summer or early fall. These features seemed most compatible with an arthropod-vectored illness (insects or arachnids).
Many patients reported an expanding lesion, identified as erythema migrans (EM) around the area thought to be an insect bite. In Europe, erythema chronicum migrans (ECM) was described in 1909, and is associated with the bite of Ixodes ticks. Patients in Europe presenting with ECM often later showed signs of neurologic abnormalities, but not arthritis. Later studies following patients with EM in Connecticut found many developed arthritis, but also neurologic or cardiac abnormalities. Thus the illness in Lyme residents was thought to be a previously unrecognized clinical entity, a complex, multi-system disorder named Lyme disease.
The identification of patients with EM also helped identify the domestic vector of the disease. Many patients remembered being bitten by a tick the site of EM a median of 12 days before symptom onset. One patient saved the implicated tick and it was identified as Ixodes scapularis or the black-legged tick. Field surveys showed high abundance of the ticks on white-footed mice and white-tailed deer. Subsequent studies into the vector and affected patients revealed the disease agent, the spirochete Borrelia burgdorferi in the early 1980's.
Since its discovery in the early 1980's, Lyme disease has become the most reported vector-borne disease in the United States. In 2000, approximately 16,000 cases were reported to the Centers for Disease Control and Prevention. This increase in cases is due to many factors, including (but not limited to):
Increased surveillance and understanding of the disease system
The movement of people out of cities into more rural environments brings them into close proximity with the preferred habitat of the black-legged tick
Forest fragmentation and increasing deer populations
Dispersal of the black-legged tick into new, receptive habitats
Lyme disease is now endemic (prevalent) in the Northeast and much of the North Central United States including Wisconsin, Illinois, Indiana, and Pennsylvania. Lyme disease is also endemic in the Northwest United States, being vectored by Ixodes pacificus, the western black-legged tick. CDC's national Lyme disease risk map. Historically, the only endemic region in Michigan has been Menominee County in the Upper Peninsula, bordering a highly endemic region of Wisconsin. Recently, however, populations of infected black-legged ticks have been found in Western Lower Michigan.
In Michigan, the first official reported human case of Lyme disease was in 1985. Cases have now been reported in both the upper and lower peninsula and are increasing. It is anticipated that the number of cases reported will continue to increase due to public and medical personnel education, and expanding tick ranges. It is always prudent, to use precautions when recreating in wooded areas. Over the counter products containing DEET or permethrins ARE EFFECTIVE against ticks.