The Medical Minute: Lyme disease upswing expected

June 21, 2005

By John Messmer
Penn State Family and Community Medicine
Penn State Milton S. Hershey Medical Center
Penn State College of Medicine

It's Lyme disease season again, particularly in the northeast United States. Last year in Pennsylvania there were 903 reported cases of Lyme disease and reports are on course to exceed that number this year according to the Centers for Disease Control. To understand how many cases that represents, compare it to 642 reported cases of AIDS and 124 cases of tuberculosis.

Most people know ticks transmit Lyme disease, but there are other tick-borne illnesses including Rocky Mountain Spotted Fever (12 cases in Pennsylvania in 2004), ehrlichosis and more. Lyme disease is named for the town of Lyme, Conn., where a cluster of cases in the 1970s was linked to tick bites. It is believed Lyme disease was introduced into the United States by a herd of deer brought from Europe in the early 20th century.

Lyme disease is only carried by the Ixodes or deer tick. When tick eggs hatch, the newborn tick is called a larva. It looks like a tick but is only the size of a period on this screen. The larva stays on the ground until it can attach to a passing bird or mammal, typically a mouse, from which it feeds. Larvae are not born infected with Lyme, but may contract it from this feeding if the animal is infected. Since ticks do not pass on Lyme until they feed and because larvae do not feed again, they are not a threat to us.

Tick larvae live and grow in the ground until the following spring when the temperature rises above 40 degrees. About 25 percent of nymphs carry Lyme organisms. During peak times from May to July, nymph ticks climb onto grasses then attach to a passing animal, such as, a deer, bird, dog or human which brushes against it. Ticks do not jump or fly to hosts. The nymph, about the size of a sesame seed, will look for a place on its host to attach and feed. The tick attaches itself with an adhesive secretion and takes up to three days to feed. Disease can only be passed during feeding. Nymphs are often unnoticed until after feeding when they are swollen with blood. If not removed, they fall to the ground and grow into adults.

Adult ticks climb tall grasses and shrubs to continue to look for other hosts on which to feed until winter. They resume the following spring when they mate and die. About 50 percent of adult deer ticks carry Lyme which they contract from one of their feeding sources, but they are not usually responsible for transmitting it to humans since they are large enough for us to see and feel on our skin.

The risk of tick bites can be reduced by understanding where they are most active. Dense, mature woods with thick underbrush and small trees are the most likely place to find them. Well-mowed lawns discourage ticks because lack of vegetation makes it too hot and dry. Birdbaths, woodpiles, brush piles, stone fences, tree houses and swing sets and woods surrounding a yard are high-risk places for ticks. In addition, pets coming indoors from these areas may carry ticks into the house.

When one is in a high-risk area, light-colored clothing makes the dark ticks easier to see. Tuck long pants legs into socks and use a tick repellant containing DEET or permethrin to reduce the chance of picking up a tick. A veterinarian can help with an appropriate tick treatment for pets.

After exposure to potentially tick infested areas, remove all clothing and closely inspect the entire body for ticks. Crawling ticks are no threat and can be removed easily. If the tick is attached, grasp it with fine tweezers and gently pull. The adhesive will look like skin as it pulls away, but it might take a few seconds for the tick to release its bite. Do not try to burn the tick or apply Vaseline or other chemicals, simply pull it off slowly. Wash the area with soap and water. If the tick if flat, it did not feed and did not spread Lyme disease. If it is swollen, it may have transmitted disease. Seek medical care within a day or two and if possible, take the tick along in a secure container or plastic bag.

Too often, symptoms begin without noticing a tick bite. Most of the time a red ring develops within weeks of the bite, but it may be in an area that is not easily seen. If untreated, in the next few weeks, a flu-like illness without sore throat or respiratory symptoms develops, but since the flu does not occur in the warm weather, medical evaluation should be obtained. Most cases of Lyme disease are easily treated with antibiotics.

Untreated, Lyme disease can cause damage to the nervous system, heart and joints. There is a blood test for exposure to Lyme, but it takes a few weeks after infection to become positive and is best used to confirm suspected cases.

This summer, remember to take precautions to reduce the risk of Lyme disease in your family. For more information on Lyme disease, go to http://www.hmc.psu.edu/healthinfo/jkl/lymedisease.htm online.

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Last Updated March 19, 2009