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by Jerome Levine, MD
Vector of Transmission and Animal Hosts
Clinical Signs
Within a week at the site of the tick bite, the vase majority of patients will develop ECM. The skin lesion begins as small red raised lesion, and then begins to expand with central clearing. It may feel hot to the touch, but is usually not painful. The most common sites for this lesion are the thigh axilla, groin and head. This rash is frequently accompanied by a flu-like illness, with malaise, headache, fatigue, chills and fever. The symptoms may actually wax and wane during this early stage of infection.
Within several weeks of untreated disease, about 15% of patients will develop some neurologic abnormalities, such as facial palsy, meningitis, and encephalitis. Occasionally, after a long latent period, some individuals develop chronic neurologic manifestations of the disease, such as a subacute encephalopathy, where they have severe changes in their mood, memory, and behavior.
Also within the same time period, 5% of untreated patients develop cardiac problems. These are usually irregularities of the heart rhythm, known as heart blocks. They are generally benign and cause no clinical symptoms..
The vase majority of infected, untreated patients have the onset of joint symptoms, ranging from subjective pain to attacks of frank arthritis and eventually to a chronic erosive arthritis. The larger joints are primarily involved, especially the knees. Fortunately, though 80% of infected individuals develop these symptoms, only a small percentage go on to chronic Lyme arthritis, defined as 1 year or more of continuous joint inflammation.
Diagnosis
The diagnosis of LD is based primarily on the characteristic clinical picture in a patient from an endemic area. A history of a tick bite is frequently unknown and culture of B. burgdorferi is a very low yield, expensive procedure not available to the clinician. Thus, the physician must sometimes utilize serologic tests to aid in the diagnosis. However, these blood tests have not been standardized, and false-negative and false-positive results as well as interlaboratory differences in documented, frequently aided by well meaning, but poorly educated consumer support groups. Newer diagnostic testing, such as the polymerase chain reaction, will hopefully aid in the diagnosis of active lyme infection, but supportive studies are needed.
It is helpful if the tick can be saved to determine if it is a deer tick, and not the more common wood tick. Your doctor can bring the tick to the Microbiology Lab at HUMC and have it analyzed. However, only your physician can make a clinical diagnosis of LD. The Dept. of Health of NJ has published a very useful monograph for physicians to help them understand the complexities of diagnosing LD and utilizing and interpreting the currently available serologic tests.
Treatment
Generally, oral antibiotics are highly effective in treating most manifestations of LD. These antibiotics include doxycycline and amoxicillin. Intravenous antibiotics, such as ceftriaxone, should only be used in cases of objective neurologic abnormalities, certain cardiac manifestations, and occasionally in patients with arthritis unresponsive to oral treatment. Other newer antibiotics, such as the macrolides, Zithromax and Biaxin, may be useful. Unfortunately, since the organism cannot be cultured and in vitro sensitivity tests run, good clinical studies to determine the best antibiotic regimens have not been done. Most data tends to be anecdotal and very difficult to interpret.
Even more difficult to diagnose and treat are the small percentage of patients with LD who develop either the clinical syndrome fibromyalgia or chronic fatigue syndrome. These illnesses do not seem to respond to antibiotic therapy. However, it is important to understand that some patients carrying this diagnosis do not actually have lyme infection. Again, one should be very careful in making such a diagnosis based strictly on blood serology for LD. Your physician may want to get a second opinion from an expert in Lyme Disease.
Prevention
The risk of tick bites in endemic areas can be reduced by simple measures: wear long pants tucked into your socks; check for ticks after exposure to woods, including searches in your children (look especially in the head and neck region of small children). Insecticides containing DEET may be useful, but they should be carefully applied as serious side effects may occur if applied in excess to the skin. Permethrin also can be use, but is only applied on clothing. The deer tick is very small, approximately the size of a pin head. When attempting to remove it from the skin, a tweezers should be used and the tick gently pulled straight out, without leaving any part in the skin.
The question of whether to treat patients with a tick bite with prophylactic antibiotics is also very controversial. Conflicting studies have been published in this area. Your physician is best qualified to discuss this matter on a case-to-case basis, as no clear consensus guidelines have been established.
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LYME DISEASE
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Lyme Disease (LD) is a multisystem disorder caused by the tick-transmitted spirochete Borrelia burgdorferi. The disease was first recognized in 1975 because of a geographic cluster of children with arthritis in Lyme, Connecticut. LD usually begins in the spring with a characteristic bite (early Lyme). Within several days to weeks, in untreated patients, the organism may spread to many other body sites, such as to other skin areas, the nervous system, heart, or joints (disseminated disease). After many months to years following a long period of latent infection, the spirochete may cause persistent disease, affecting the joints, nervous system or skin (late disease). Yet, it is important to understand that all stages of the disorder are usually curable if diagnosed and treated with the appropriate antibiotic therapy.
The vector of Lyme borreliosis (another name for LD) in the Northeast is the ixodid tick I. dammini. In some areas of our region, such as Shelter Island, NY, 50 percent of all these ticks harbor the spirochete pathogen, B. burgdorferi. The peak feeding period for the tick nymph, which is primarily responsible for transmission of LD, is May through July, though all stages of the tick may feed on humans. For transmission of the infection to occur, the tick must be attached and feeding for at least 24 hours. The immature tick feed primarily on rodents, such as the white-footed mice, and adults usually feed on larger mammals, such as deer. The human is an accidental carrier and not a natural host in the tick life cycle.
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Written by Dr. Jerome Levine, M.D.
Development: Peter J. DeMauro, M.D.
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