Double Cone Quarterly
Fall Equinox 2003-- Volume VI, Number 2

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Lyme Disease
By William H. Johnston, M.D.

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Named for Lyme, Connecticut, where it was first described in the 1970's, Lyme disease is caused by a corkscrew-shaped bacterium called Borrelia burgdorferi (BB), which in California is transmitted to humans by the bite of the western black-legged tick, Ixodes pacificus (IP), The incidence of Lyme disease is low in Monterey County, with 5 cases having been reported to the Monterey County Health Department in 2002 and 2 cases in 2001, in a population of approximately 409,000 people. In contrast, more than 18,000 cases were reported nationwide in 2002, mostly in a few heavily wooded regions in the Northeast and parts of Wisconsin and Minnesota, making it the most commonly reported insect-transmitted disease in the United States.

The Bacterium. BB is a spirochete (from the Greek words for spiral and hair), a member of the same family of bacteria that includes the organisms that cause syphilis. As a matter of fact, the course of Lyme disease is quite similar to syphilis, in that an initial skin lesion may be followed by pathological changes in almost any organ system as the organism proliferates and disseminates throughout the body. The BB bacterium has surface proteins that allow it to attach to mammalian cells, and apparently depends on the host for most of its nutritional requirements. Outside of the United States, other species of Borrelia cause Lyme disease.

The Tick and Its Bite

IP is a hard tick that has larval, nymphal, and adult stages (Figure 1).

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Figure 1

Each life stage of the tick bites and attaches to an animal for several days to take one blood meal before maturing to the next stage. In California (and Oregon), the spirochete is maintained in nature by the dusky-footed woodrat and another species of ticks which does not bite humans. Larval and nymphal IP ticks prefer to feed on lizards, which are not susceptible to BD spirochete infection; however, they occasionally also feed on woodrats infected with the BD spirochete (as well as birds, which are not infected). Adult IP ticks usually feed on medium sized to large mammals such as deer, but occasionally on humans.

Only the relatively few nymphal and adult IP ticks that fed on infected woodrats when they were in the preceding stage are responsible for the transmission of the BB spirochete to humans; hence the low rate of Lyme disease in the west.

In contrast, in the northeastern and north central parts of the United States, abundant nymphal deer ticks become infected with BB from infected wild mice, and then bite humans in a highly efficient cycle of transmission. As a result, the frequency of Lyme disease in humans is high during the late spring and summer months in these parts of the country.

In Monterey County, larval and nymphal IP ticks are found in low, moist vegetation such as leaf litter, so that hikers will probably encounter IP nymphs while camping or resting along the trail. Adults, in contrast, are found on the tips of grasses and shrubs, so that hikers will most likely encounter IP adults on the trail. Ticks do not jump or fly, but rather crawl onto their victims directly from leaf litter, or position themselves on low-lying vegetation and climb aboard as passing people and other animals brush against the vegetation.

IP is a small tick at all stages of development, with the largest being the engorged female (Figure 2).

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Figure 2

Nymphs can pose a greater risk of transmitting Lyme disease to humans because they are about the size of a poppy seed and are difficult to find. However, the adult female is not that much larger. The larger ticks that we encounter when hiking and camping are probably Pacific Coast, Pajahuello, or American dog ticks, which do not carry Lyme Disease.

The IP tick must be attached for at least 24 hours in order to transmit the BD spirochete to humans. One study demonstrated that when the tick had fed for less than 72 hours, there was no infection with BB. Thus, there is a grace period during which simple removal of the tick prevents infection. The tick becomes engorged with blood as it feeds, making the enlarged tick more noticeable.

How The Disease Presents and Develops

Ordinary tick bites usually cause local pain, redness, and sometimes pain (Pajahuello ticks) that occurs less than 24 hours after the bite and does not expand. This represents a local reaction to the proteolytic enzymes and anticoagulants in the tick saliva that is injected by the tick to break down skin tissue and permit the intake of blood from damaged blood capillaries. The local reaction usually subsides in less than a week, although if the head or mouth parts of the tick remain attached, there may be an itchy bump that lasts much longer (personal experience).

In contrast, a bite from the IP tick which transmits the BB spirochete causes a conspicuous target-shaped lesion called erythema migrans (EM) in at least 80% of infected individuals (Figure 3).

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Figure 3

EM appears 1 to 30 days after the bite of an infected tick, expands over a 1 to 2 week period, and then disappears. More EM lesions can show up later, not necessarily at the site of the tick bite, hence the term "migrans". EM is usually painless and varies in shape and appearance. On dark skin, the EM can look more like a bruise. If EM may occurs on a part of the body such as the scalp that is difficult to see, it may be missed.

The skin lesion is frequently accompanied by other early (acute) symptoms such as a flu-like illness (even though it's not the flu season), malaise and fatigue, headache, joint pains, muscle pains, fever, or swelling of lymph nodes in the vicinity of the bite. Other early symptoms include sudden arthritis in the large joints, sudden sciatica-like pain or other nerve inflammation, facial paralysis, or abnormal heart rhythm. These symptoms may be the presenting manifestation rather than EM, which sometimes does not appear (up to 20% of cases).

If not treated, Lyme disease can cause a variety of late (chronic) symptoms including other forms of skin rash. Swelling and pain of one or a few joints may occur, especially the knees, may move from one joint to another, and may come and go. Neurological symptoms may include numbness, tingling, or burning sensations in arms and legs; twitching, weakness, or paralysis of the face, arms, or legs; sharp pain in the arms, legs, neck, and back; increased sensitivity to light; difficulties with memory, concentration, learning, or speech; mood swings, depression, or abnormal thought processes.

Diagnosis

Lyme disease diagnosis is based upon the recognition of the characteristic clinical findings as described above, a history of exposure in an area where the disease is endemic, and detection of an antibody response after the first several weeks of infection. Direct culture of the BB bacterium is difficult and unreliable, especially in later stages of the disease.

As an adjunct to clinical diagnosis, the Sonoma County Health Department Laboratory will test suspected ticks for the presence of the BB bacterium for a fee (currently $29). To arrange for this, call the laboratory directly at 707-565-4711. (The first recognized human case in California occurred in 1978 in a hiker from Sonoma County).

Treatment

Prompt treatment with antibiotics early in the course of the infection usually cures Lyme disease. This should be supervised by a physician, who can customize the treatment to fit specific circumstances. As examples, a person allergic to one antibiotic would then be given an alternative, and some antibiotics should not be administered to children and pregnant women. About 10% of patients continue to have arthritis after treatment, and a small percentage continue to have subjective symptoms such as musculoskeletal pain, neurological difficulties, or fatigue that may last for years. Prolonged antibiotic treatment has been shown to be of no help and may cause severe side effects on its own.

Delayed treatment with antibiotics is less successful, and recovery may take longer. For this reason, it is important to see a physician promptly if you suspect that you might have contracted Lyme disease.

Self medication with antibiotics in a disease as complex as this is inadvisable. Since the risk of Lyme disease in Monterey County is very low, prophylactic antibiotic treatment following a tick bite is unnecessary and unwise, especially if the tick has been attached for a short period and is not engorged with blood.

If a course of antibiotics is prescribed by a physician, usually over a course of 14 to 21 days, it is important to take all of it over the entire length of time prescribed to effectively eradicate the BD bacteria and prevent development of chronic disease and resistant organisms.

A vaccine against Lyme disease was once available, but has been withdrawn from the market due to dwindling sales, possibly because of a class-action lawsuit maintained that the vaccine increased the risk of developing arthritis.

Practical Considerations

Wear long-sleeved shirts and long pants, with pant legs tucked into boots and socks if possible. Light colored clothing makes it easier to see and remove ticks before they bite. Tom Hopkins has observed that coarsely woven clothing attracts more ticks, probably by providing a rougher surface that the ticks can grab onto more easily. He also notes that the lead person on a hike tends to attract more ticks than those following; first come, first served, as it were. Some recommend staying to the middle of the trail to avoid brush where ticks may be waiting, although this is obviously quite difficult on the overgrown trails of the Ventana Wilderness. Carefully inspect your entire body for ticks following a hike.

Insect repellents containing DEET are effective in repelling ticks, although profuse sweating on a strenuous hike might make it difficult to maintain adequate coverage for any length of time. Please see the May, 2003 issue of Consumer Reports (page 15) for specific brand name recommendations.

Ticks should be removed with tweezers applied to the head of the tick as close to the skin as possible to permit complete removal (Figure 4).

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Figure 4

Gentle pulling is the most effective means of detaching the tick. Other methods such as burning the tick or suffocating it with petroleum jelly are not effective.

SUMMARY

The risk of contracting Lyme disease in Monterey County is small. Tick avoidance and early removal of tick remain the best lines of defense against Lyme disease. The tick must be attached for at least 24 hours to transmit the disease, so that a careful search for ticks after a hike and their prompt removal should prevent infection. One should be aware of the signs and symptoms of Lyme disease and should consult a physician promptly if there is any suspicion of having contracted the disease.

YOUR INPUT IS REQUESTED

Please send me any comments or personal experiences you have had with Lyme disease, and I will incorporate pertinent ones in future updates of this article. My e-mail address is: william.h.johnston@kp.org.

REFERENCES AND SOURCES OF INFORMATION

1. California Department of Health Services online article "Lyme Disease in California", http://www.dhs.ca.gov/ps/dcdc/disb/disbindex.htm (scroll down to the section on Lyme Disease, and click the link to download the Adobe PDF document).

2. Consumer Reports, May, 2003

3. Steere, Allen C: Lyme Disease. N Engl J Med, Vol 345, pp 115-125, 2001.

4. Vredevoe, L: "Ticks Commonly Encountered in California", online article, http://entomology.ucdavis.edu/faculty/rbkimsey/caticks.html


© 2003 by William H. Johnston, M.D.
Illustrations courtesy California Department of Health Services

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