Some of you who spend time in the great outdoors of Northeast Florida may wonder about your risk of exposure to Lyme disease and the need for vaccination.
Lyme disease (LD) was first recognized in 1975 while researchers were investigating children with early arthritis near Lyme, Connecticut. Subsequently, LD was found to be caused by bacteria transmitted by the local deer tick. It is not spread by animals or by contact with mosquitoes. LD is now the most common tick-borne illness in the United States and is widespread in northern and central Europe. It has been described in Asia, Australia, China, Japan, and the Soviet states.
In the United States, over 90% of reported cases occur in the Northeast, Mid-Atlantic, and North-Central regions (Figure 1).
Figure 1. LD
Figure 1. LD incidence, 1997.
Because ticks transmit LD, it helps to understand some background on the lifecycle of these ticks. There are over 800 different types of ticks known, but only a few species, mainly Ixodes scapularis in the East and Midwest and Ixodes pacificus in the West carry Borrelia burgdorferi, the bacteria which causes LD.
This black-legged or deer tick has a 2-year life cycle. First, the eggs hatch into larvae that feed on birds, lizards, and mammals. The larvae eventually molt into nymphs. The larvae and nymphs prefer small mammals, especially the white-footed mouse in the Northeast and reptiles such as the lizard in the Southeast. Because the lizard is incompetent as a bacteria reservoir, the incidence of LD in the southeastern states is only a small fraction of the total cases of LD.
Nymphs, about the size of a printed period (Figure 2), then molt into adults, about the size of an apple seed, which prefer to feed on larger mammals, particularly white-tailed deer. Both nymphs, which feed for 3 days, and adults, which feed for 7-9 days can attach to humans and feed on blood by inserting their mouthparts into the skin. Ticks search for animals by crawling from the tips of grasses and shrubs. They do not fly or jump. Less than 20% of those diagnosed with LD remember a tick bite.
Figure 2. Nymph (left) and adult deer ticks.
The diagnosis of LD is difficult and can be confused with other infections or arthritis conditions. First, all bites, from any kind of tick, create a small amount of redness, usually less than 2 inches. Second, most people dont recall how long a tick was embedded in their skin. Ticks must feed for at least 24-48 hours before transmission of the offending bacteria. Third, only a small percentage of ticks that carry the bacteria transmit it to humans. And fourth, the lab results are sometimes deceiving.
Two main lab methods are used: the initial ELISA which detects early and late antibodies in the blood, and the Western blot which may help confirm or deny the results of the ELISA. The ELISA is usually negative in the first 4-6 weeks of the illness and depending on lab methods may miss recognition altogether. The Western blot will be negative if antibiotics are used early in the illness and is a difficult procedure to standardize from one lab to another.
The Center for Disease Control recommends stopping testing if the ELISA is negative. If the ELISA is positive or unsure, then Western blot should be performed. The most common and reliable means of diagnosis is the finding of the erythema migrans (Figure 3) or bulls eye rash at the initial bite site. This rash (usually over 2 inches in diameter) found often on the scalp, underarm, navel, groin, or thigh can develop 3-30 days after a tick bite and can be accompanied by mild flu-like symptoms.
Figure 3. The classic erythema migrans lesion.
Erythema migrans will present in up to 80% of LD infections which, with medical confirmation and appropriate treatment, will prevent further complications.
Weeks to months into an untreated infection, the second stage of LD develops. This stage affects the nervous system and the heart. Symptoms can include fever, stiff neck, weight loss, dizziness, memory loss, abnormal mood and/or heart palpitations.
If the illness continues unrecognized and untreated, stage 3 LD develops. In stage 3, arthritis in one or several joints, most frequently the knee, can present months to years following the initial bite. For some this may be the first manifestation of the illness.
Treatment can be initiated at any stage starting with oral antibiotics, typically doxycycline or amoxicillin for brief periods early on which cures about 90% of those with early LD. Extended duration oral or intravenous antibiotics such as ceftriaxone are used for more advanced stage LD. With all of the complexities involving diagnosis and treatment of LD we must focus on how can LD be prevented.
The FDA approved Lymerix (www.lymevaccine.com), the first vaccine for prevention of LD, in December 1998. The antibodies produced by vaccination destroy bacteria in the gut of the tick before it can be transmitted to the host.
Lymerix is given at 0, 1, and 12 months and confers approximately 80% protection. We dont know how long the vaccine protects or how often to give boosters, but this is a significant advance in our war on LD. The vaccine presents its own challenges. We know that not all who are bitten get LD and experts fear that vaccination may replace simple precautions. Overuse of LD vaccines may render them less effective in the long run. A vaccine that works in one area of the country may not be as effective in another. Some researchers fear LD vaccines may cause Lyme arthritis. Finally, the antibodies produced by the vaccine may cause confusion in the interpretation of lab diagnosis of LD.
Current recommendations call for vaccinating only those at significant risk of contracting LD such as rangers, birdwatchers, and frequent outdoors persons in high-risk areas such as Connecticut. It is generally not recommended that those living in Northeast Florida get the vaccine.
The vaccine garners a lot of attention but carries little weight compared to other preventive measures. The 12th International Conference on Lyme Disease in April 1999 confirmed that prevention is the key to effective control of LD. When outdoors, wear bright clothes, long sleeves and pants; tuck pants into socks, tape cuffs, spray self with an insect repellent containing 10% DEET and clothes with permethrin, walk in the center of the trail, and daily check entire body for ticks.
If you live in a potential risk area, erect deer fences, remove plants that deer eat, remove leaf litter and tall grass, consider an acaricide and/or wood chips in the transition zone between wooded and living areas, and check pets regularly.
If you find a tick, first grasp the head of the tick with tweezers or forceps and pull with steady traction making sure not to crush the tick and inject it's contents into your body. After the tick is removed, wash the bitten area and your hands with alcohol or soap and water.
Do not use the old methods of removal such as Vaseline, kerosene, nail polish, or matches as these may cause the tick to spew bacteria into the wound.
In conclusion, LD and other tick-borne illnesses pose real health risks. The diagnosis and treatment of LD is sometimes perplexing. As we spend time where ticks live, we must educate ourselves to take precautions and hopefully interrupt the disease progression and potential disability resulting from LD.
American Lyme Disease Foundation, 293 Rt. 100, Suite 204, Somers, NY 10589
Centers for Disease Control, voice information: (404) 332-4555
Arthritis Foundation, 1330 West Peachtree St., Atlanta, GA 30309
Your local physician or health department