Lyme disease: tick terror - includes related article on Lyme disease in dogs and cats

Harvard Health Letter, July, 1991 by Patricia Thomas

In the 14 years since it was named Lyme disease, this illness caused by tick-borne bacteria has become a national concern sometimes verging on obsession. Public-service announcements run on television and in move theaters. People who have been bitten by ticks spend a few days or weeks worrying about getting sick. And an entire subculture has grown up around chronic Lyme disease.

At first, Lyme disease seemed to occur only in certain prime vacation spots: Cape Cod and eastern Long Island in the Northeast, the North Woods of Minnesota and Wisconsin, and less frequently, the northern California coast and Oregon. Although 97% of cases continue to come from only nine states, 46 states in all have reported occurrences to the Centers for Disease Control during the past decade. In 1989, the last year for which statistics are available, the number of new cases reported was 8,552.

Aiming at the bullseye

Diverse symptoms and a variable course make Lyme disease difficult to recognize. The initial event, a tick bite, may not be noticed, in part because the tick itself is no bigger than the size of the period at the end of this sentence. Most patients don't recall being bitten or even seeing the culprit.

If symptoms appear, the best person to consult is one's personal physician, according to Raymond Dattwyler, an expert on Lyme disease and an associate professor of medicine at the State University of New York at Stony Brook. Primary-care physicians are able to diagnose most Lyme infections and give appropriate treatment, and they are in the best position to make referrals, if need be, to reputable specialists in infectious disease or rheumatology.

The most reliable way for a physician to diagnose the illness is to evaluate the patient's physical symptoms andsigns in light of his or her risk of exposure. In 60-80% of cases, the disease announces itself with a so-called bullseye rash, or erythema migrans -- a rim of painless reddened skin expanding around a pale area centered on the site where the tick (by now long gone) originally attached itself. the ring of red must be at least two inches across to meet the standard criterion of erythema migrans. Such a ring can expand to reach 20 inches in diameter, and additional ones may subsequently appear inside it in a targetlike pattern. After a few days similar rashes may show up elsewhere on the body. Fever and flu-like symptoms are often present early in the illness.

Unfortunately, the blood tests available for diagnosing Lyme disease are far from perfect. They rely on detecting antibodies, which may only reach measurable levels after three or four weeks of infection. Once they have developed, the antibodies persist for years and may thus create a false impression that the patient has an active case. Moreover, certain other illnesses that are easily mistaken for Lyme disease, such as rheumatoid arthritis or lupus erythematosus, can give positive results, as can gum infections caused by distantly related bacteria. Even in regions where Lyme disease is prevalent, screening 1,000 people for the disease would yield only one true-positive result while giving 20 false positives. Consequently, physicians must still rely on clinical evidence much more than laboratory data to identify people with Lyme disease.

In areas of high prevalence, doctors often have to make judgments about two types of patients -- those hwo find a tick on themselves but have no symptoms, and those with suggestive symptoms or a rash that could be erythema migrans but is not typical. Patients with just a tick bite should probably not be treated unless symptoms develop. From experiments in mice, it appears that infectious ticks must remain attached for more than 24 hours in order to transmit Lyme disease. If a tick is spotted and removed before it drops off spontaneously, transmission is likely to be prevented. The probability of developing Lyme disease after noting a tick bite is about the same as the likelihood of developing an adverse reaction to medication. On the other hand, treating suspicious symptoms, including a suggestive rash, is nt unreasonable, even though it may lead physicians to treat some patients unnecessarily. Such decisions must always be individualized, however.

Oral antibiotics (usually tetracycline, doxycycline, or amoxicillin) are almost always curative when given promptly. They must be used for at least ten days, although some physicians prefer to continue them for up to a month.

If the diagnosis is missed or treatment is started late, the Lyme bacteria may produce a second stage of the illness after several weeks or even months of quiescence. About 15% of untreated patients develop neurological abnormalities. A fairly common problem is temporary paralysis of muscles on one or both sides of the face (Bell's palsy). There may also be symptoms of meningitis (sudden fever, headache, stiff neck, and vomiting), movement abnormalities, or pain originating in a nerve root, among other difficulties. About half as frequently the heart is involved -- often with slowing of the pulse. Generalized inflammation of the heart or its covering membrane causes some patients to experience chest pain or shortness of breath. Usually the heart improves spontaneously in a few weeks. During this phase, antibiotics are still very effective in eradicating the disease from the vast majority of patients. Depending on the severity of symptoms, the drugs can be given orally or intravenously for two to four weeks.