The Facts about Lyme Disease

Lyme disease is an illness caused by a bacterium, Borrelia burgdorferi, that is transmitted by a tick named Ixodes scapularis (commonly called the deer tick). The first cluster of cases associated with this infectious agent was discovered near the town of Lyme, Connecticut (thus the name).

Lyme disease may cause symptoms affecting the skin, nervous system, heart and/or joints of an infected individual. More than 7,000 cases of the disease have been reported in Wisconsin since surveillance for Lyme disease began in 1980.

Anyone can get Lyme disease. People who spend time outdoors in tick-infested environments are at an increased risk of exposure. Most cases have reported an exposure to ticks or woodland/brush habitat during the months of May through August, but exposure can occur whenever the temperature at ground level is warm enough for ticks to be active. In Wisconsin, the vast majority of cases have been acquired in the western two-thirds of the state. The northwestern and west central portions of Wisconsin have the highest incidence of the disease.

Transmission
Lyme disease is spread through tick bites. The deer ticks that transmit the Lyme disease bacterium become infected when the immature stage of the tick feeds on infected field mice. When the tick feeds again, the infection can be transmitted to the tick's new host - often, a human. The tick must actually be attached to a person's skin for about 24 hours before it can transmit the bacterium. The bite of the tick is usually painless, making it more difficult to detect. That's why it's important to do a thorough body check for ticks after being in areas where ticks are likely to live.

Occurrence
In a CDC report summarizing the analysis of 40,792 cases of LD reported to CDC during 2001 - 2002, patients were most likely to have illness in May (7%), June (28%), July (31%), or August (12%). Fewer than 7% were reported to have illness onset during December to March.

In 2001, a total of 17,029 cases of LD were reported to CDC by 43 states and the District of Columbia, yielding a national incidence of 6.0 cases per 100,000 population. In 2002, the number of reported cases increased 40% to 23,763 cases, yielding a national incidence of 8.2 cases per 100,000 population. All states except Hawaii, Montana, and Oklahoma reported cases during 2002.

Twelve states reported an incidence of LD that was higher than the national average in both 2001 and 2002: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Wisconsin. These 12 states account for 95% of cases reported.

In Wisconsin, the number of cases of Lyme disease rose gradually through the 1990s, from 401 in 1993 to 597 in 2001. Then, as in many other states, there was a giant leap to 1,090 reported cases in 2002, yielding an incidence of about 20 cases per 100,000 people.

Symptoms
The illness usually occurs during the summer months and often - but not always - starts as a roughly circular reddish rash (called erythema migrans) around or near the site of the tick bite. The rash expands in size over a period of days or weeks, often from 4 to 12 inches in diameter or even larger. During the rash stage, other symptoms such as fever, headache, fatigue, stiff neck, muscle and/or joint pain may be present. These may last for several weeks.

If left untreated, within a few weeks to months after the rash onset, complications such as meningitis, facial palsy, heart abnormalities, and arthritis may occur. Swelling and pain in the large joints may recur over several months or years in untreated Lyme disease. Not all persons with the disease develop the initial skin rash.

The CDC report mentioned above found that among 31,120 patients for whom at least one clinical finding was indicated, a history of erythema migrans was reported for 21,126 (68%) patients, arthritis for 10,126 (33%) patients, Bell's palsy (paralysis of the facial nerve) for 2,510 (8%) patients, and radiculopathy (disease of the nerve roots) for 1,009 (3%) patients. Meningitis, encephalitis, and heart block were reported in <1% of patients.

Early symptoms of Lyme disease usually begin within a month of exposure. The later arthritic, cardiac, and neurologic problems can take weeks to months to appear.

Treatment
The disease is treated with oral or injectable antibiotics.

Past infection does provide some immunity, but that protection is relatively short-lived. It is possible for a person to get infected more than once.

Prevention
The continued emergence of LD underscores the need for persons in areas where LD is endemic to reduce their risk for infection through integrated pest management, landscaping practices, repellent use, and prompt removal of ticks.

If you are in areas where ticks may be present, the following precautions can reduce the risk of acquiring Lyme disease:

• Wear a long-sleeved shirt, long pants, and high socks with pant cuffs tucked into the socks. Light colored clothing will make ticks easier to find. Walk in the center of mowed trails to avoid brushing up against vegetation.
• Conduct thorough "tick checks" on yourself and your children after spending time outdoors. Prompt removal of ticks, even after they have attached, can drastically reduce the chance of Lyme disease transmission.
• Insect repellents containing 0.5% permethrin or 20-30% DEET have been shown to be effective in repelling deer ticks. If such products are used, be sure to follow the manufacturer's directions on the label.
• Clear leaf litter from yard; put a border of gravel or wood chips around perimeter as a buffer between forest and lawn.
• Newly available bait boxes can be placed around outside of yard. When tick-carrying rodents enter the box, they're dosed with insecticide that kills the bugs.

Although there had been a vaccine against human Lyme disease, it is no longer marketed.

Tick Removal
To remove an attached tick, grasp it with narrow-bladed tweezers or forceps as close as possible to attachment (skin) site, and pull upward and out with a firm and steady tension. If tweezers are not available, use fingers shielded with tissue paper or rubber gloves. Do not handle with your bare hands. Be careful not to squeeze, crush or puncture the body of the tick - it may contain infectious fluids. After removing the tick, thoroughly disinfect the bite site and wash your hands. See or call a doctor if there is a concern about incomplete tick removal. It is important that a tick be properly removed as soon as it is discovered.

Information provided by the Centers for Disease Control and Prevention and the CDC's Morbidity and Mortality Weekly Report.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.