Lyme Disease Incidence Doubles

Since 1991, the annual number of cases of Lyme disease reported in the US has more than doubled. More than 21,000 cases of the tick-borne disease are now reported every year, making it the most common illness transmitted by bugs or animals in the United States. And these numbers are probably underestimated, says the US Centers for Disease Control and Prevention (CDC).

Lyme disease is caused by a bacterium, Borrelia burgdorferi, that is transmitted by deer ticks (Ixodes scapularis). It occurs primarily in northeastern, mid-Atlantic, and north-central states, peaking during the summer months of May through August. The first cluster of cases associated with this infectious agent was discovered near the town of Lyme, Connecticut.

The disease is considered endemic in 10 states: Connecticut, Delaware, Maryland, Massachusetts, Minnesota, New Jersey, New York, Pennsylvania, Rhode Island, and Wisconsin. During 2003-2005, the CDC received reports of 64,382 Lyme disease cases from 46 states and the District of Columbia; 93% of the cases occurred among residents of these states. 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
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.

Anyone can get Lyme disease, but people who spend time outdoors in tick-infested environments - particularly in brushy or wooded areas - are at an increased risk of exposure. People who camp, hike, or work on gardens and other leafy outdoor areas during the summer are at the greatest risk of being bitten by ticks, but you are vulnerable whenever the temperature at ground level is warm enough for ticks to be active.

Symptoms
Lyme disease can cause symptoms affecting the skin, nervous system, heart and/or joints. 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.

The illness 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 those who get the disease develop the initial skin rash.

Treatment
Lyme disease is treated with oral or injectable antibiotics. Past infection does provide some immunity, but that protection is relatively short-lived - it is possible to get infected more than once. Patients treated with antibiotics in the early stages of the infection usually recover rapidly and completely.

Prevention
Although no Lyme disease vaccine is available, you can lower your risk for the disease and other tick-borne illnesses by avoiding tick-infested areas when possible, using insect repellents containing DEET (N,N-diethyl-m-toluamide), and performing daily self-examination for ticks. In North America, removing ticks within 24 hours of attachment reduces the likelihood of B. burgdorferi transmission.

The rising numbers of Lyme disease cases underscores the need for people to reduce their risk for infection through integrated pest management, landscaping practices, repellent use, and prompt removal of ticks.

Tick populations around homes and in recreational areas can be reduced 50% to 90% through simple landscaping practices such as removing brush and leaf litter or creating a buffer zone of wood chips or gravel between forest and lawn or recreational areas. For people who are infected, prompt diagnosis and treatment are important to prevent serious illness and long-term complications.

If you are in areas where ticks might 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.

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.

This article was reviewed by Rick Gillis, MD, Assistant Professor of Medicine and Director of the Office of Clinical Informatics at the Medical College of Wisconsin. Dr. Gillis practices at the Sargeant Internal Medicine Clinic.

It includes information from the Centers for Disease Control and Prevention and the CDC's Morbidity and Mortality Weekly Report, and the US Food and Drug Administration (FDA).

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.