Lyme disease

Introduction

Lyme disease is a relatively common, preventable and treatable disease if detected early, that may adversely affect pilotsí or controllers' careers if ignored. This article provides background information on the disease, recommendations for prevention and an overview of disease manifestations. It also outlines treatments and potential effects on pilot/controller medical certification.

What is Lyme Disease?

Lyme disease is an infection caused by a spirochete-type bacteria, Borrelia burgdorferi, transmitted to humans by a deer tick. Named after Lyme, Connecticut, where it was first reported in the mid-1970ís, the infection manifests as a multi-system disease, meaning it can affect several organ systems (joints, skin, heart, brain, nervous system) in humans. It affects people of all ages and both genders, with significantly higher risks of infection in some areas of the United States.

Many cases of Lyme disease may go unnoticed in the initial phases or may be mistakenly attributed to a mild flu-like syndrome. If left untreated, serious complications may develop. Some of these late manifestations may be difficult to treat or unresponsive to therapy. Early recognition and treatment of Lyme disease depends on a high index of suspicion about the possibility of infection and confirmatory blood testing.

Epidemiology

Lyme disease is the most common infectious disease caused by living intermediate hosts (vectors) in the United States. The Centre for Disease Control and Prevention collects reports from all fifty states on all cases of Lyme disease. In 1999, there were 16,273 cases of Lyme disease nationwide. Over 90% of the cases came from Northeastern and northern Midwestern states (Connecticut, Massachusetts, Rhode Island, New Jersey, Delaware, Pennsylvania, Maryland, Wisconsin and Minnesota). The disease is very rare in the Rocky Mountain states, desert Southwest, Alaska and Hawaii. The number of cases reported each year is increasing, partially because of increasing awareness, improved reporting, and better laboratory testing.

Because the disease is transmitted by ticks, there is a seasonal nature to infections. Most cases occur in the spring and summer. Deer ticks prefer a habitat of wooded areas and residential lawns, so most cases are acquired in rural and suburban areas. Applications of tick killing agents to a lawn will nearly eliminate the risk of disease acquisition from that area.

Lyme disease is now also reported in Europe, Asia and Australia.

Infection

The Lyme disease spirochete (bacteria) lives in the deer tick, which tends to feed on small rodents, white-tailed deer and humans. On the Pacific coast, the Western black-legged tick, closely related to the deer tick, is the carrier. The tick has a two year life cycle of four stages: the egg, larva, nymph and adult. Nymphs and adult ticks feed on blood from the host mammal. During the terminal stages of feeding, the Lyme bacteria is regurgitated by the tick into the host mammal's blood.

Because the nymph is so small, less than 1 millimetre or the size of a mechanical pencil lead, they are usually not detected on the skin. While only about one quarter of nymphs are infected with the disease-causing spirochete, they cause about 90% of human infections. Approximately one half of the adults are infected, but because of their size (sesame seed or 2-3 mm), they are more frequently detected and removed before they bite.

Most human infections are caused by ticks that have been on the skin for at least 72 hours. Infections are rare with tick exposures less than 24 hours, before the tick has had time to complete the feeding of a blood meal.

Infections occur from one to thirty days following a tick bite. The initial sign of a Lyme disease infection may be a ring shaped skin rash or a flu-like illness. Only twenty percent of people infected with Lyme disease ever recall a tick bite, so frequently an individual may attribute mild symptoms to a virus. The rash may go unnoticed since it may be small, transient, and does not cause pain or itching.

Signs and Symptoms

Three stages of infection exist for Lyme disease, the local stage, the early systemic (whole body) stage and the late systemic stage. The late systemic stages does not occur with early appropriate treatment.

Local Stage

The local stage of the disease manifests as a rash at the site of the tick bite. The rash, termed erythema migrans ("migrating redness"), starts as a red area and grows outward. It is usually flat and painless, although in some cases may burn or itch. The rash usually appears in 7-10 days after the bite, although it may appear anytime within the first month.

The rash grows slowly, over days to weeks, rather than hours as the rashes of many viral illnesses or allergic reactions. As the rash grows, it may clear in the center, giving it a "bullsí-eye" appearance. In about 20% of cases, the rash may be found in multiple areas, but is generally not found below the knees or elbows. Appearance of multiple lesions indicates the infection has spread through the blood.

Early Systemic Stage

The early systemic stage may occur simultaneously with the onset of the rash. Symptoms include mild fever, fatigue, muscle and joint aches, headache and chills. If the rash is not noticed, many people assume they have "the flu." Infected persons also may have swollen lymph nodes and a stiff neck. Unlike the flu, Lyme disease is not accompanied by cough, sneezing or a running nose.

Indications that the early systemic disease has spread include nerve palsies (loss of strength, movement or feeling in a particular area). If untreated, the neurologic symptoms may include mild confusion, meningitis or encephalitis.

Heart involvement occurs in four to ten percent of untreated individuals within the first several months of infection. Abnormalities on electrocardiograms (ECGís) are common in this group. Rarely, symptoms may include loss of consciousness, shortness of breath, congestive heart failure and skipped heart beats. These symptoms usually pass quickly, but a few individuals may require a temporary cardiac pacemaker.

Late Systemic Stage

Late systemic Lyme disease may occur months or years after an untreated infection begins. The two primary areas afflicted are the joints and the brain.

Joint pain is more common in the early stage of Lyme disease. Later stages are characterized by swelling of one or two joints, migrating to other joints. Approximately half of those individuals with untreated Lyme disease develop chronic arthritis, which may not respond to later treatment with antibiotics.

Late Lyme disease may also manifest as neurologic or psychiatric problems. There may be subtle, but progressive, deterioration in mental abilities. Treatment with antibiotics may not be helpful at this stage.

Indications for Treatment

The decision to treat Lyme disease should be made based on the presence of characteristic signs or symptoms found in a person living in or travelling through a high risk area, particularly during the spring and summer. The presence of the erythema migrans rash is a hallmark. Exposure to wooded or grassy areas without the use of insect repellant, and long sleeves, or long pants, is another factor raising the index of suspicion for infection with Lyme disease. Recall of a tick bite is not necessary, as only a fifth of patients will relate such a history.

Laboratory testing is not very useful in the early stage of Lyme disease. The spirochete is not cultured from the blood. Blood tests can detect antibodies generated by the immune system in response to an infection. However, the antibodies are not detectable for one to two months after infection and thus are useful only in proving infection after the fact. Treatment should not be delayed awaiting a positive blood test. Newer Polymerase Chain Reaction (PCR) Tests are available though expensive and may be prone to false positive reactions.

If Lyme disease is treated early, an individual may not develop antibodies. For individuals without the characteristic erythema migrans who are treated presumptively based on symptoms, blood samples are drawn at the time of treatment and several months later. Indication of infection is shown by a negative initial test for antibodies and a subsequent positive test. In the presence of erythema migrans, blood testing to prove infection is not recommended. Once an individual has antibodies detected, they will remain positive for years, and thus are not appropriate for documenting cure of the disease.

Medications

Treatment of early Lyme disease is generally very successful. Inexpensive oral antibiotics (amoxicillin, erythromycin, doxycycline) used for 10-21 days are recommended. Assuming the symptoms do not interfere with the ability to perform all flight and controller duties safely, FAA policy authorizes a pilots and controllers to return to the aviation environment while taking these medications if there are no significant side effects after two days of use. Controllers would have to obtain specific clearance from the Regional Flight Surgeon, however.

Treatment of late stage disease requires two to four weeks of intravenous therapy with different medications. Regular intravenous therapy precludes most airline pilots from flying and controllers from controlling during treatment. Private pilots receiving outpatient therapy may be able to fly, but only if the symptoms being treated are mild and do not interfere with the safe conduct of the flight.

Prevention

As with any disease, prevention is the optimum goal in protecting individuals from Lyme disease. Awareness of the disease, its mode of transmission, high-risk locations activities and seasons, and steps to avoid exposure are the keys to prevention.

The two primary means of preventing Lyme disease are taking active steps to avoid the bite of the deer tick and to obtain immunity through vaccination. Neither of these strategies are completely effective, but both can significantly reduce the risk of acquiring the disease and its complications.

Avoiding Tick Exposure

Avoiding exposure to deer ticks is, and should be, the primary means of preventing Lyme disease in the majority of people.

Persons who live in high risk areas described above should minimize travel through wooded areas, in the spring and summer. Lawns may be sprayed to kill the deer tick larva, nymphs and adults. When travelling through wooded areas, wear light coloured clothing with long sleeves and long pants. Trousers that cinch at the legs or that are tucked into socks add protection. Hats and high collars also decrease the risk of deer tick bites.

Insect repellents containing the chemical DEET should be applied to the skin (not on the face or hands of children and only in doses recommended). Permethrin may be applied to clothing, but not to skin.

Inspect the skin for deer ticks after each potential exposure. Remember that the nymphs are extremely small. If a tick is found, use a tweezers to gently remove the tick as close to the skin as possible. Do not squeeze the body. Scrape away any parts that remain in the skin and wash with soap and water.

Remember, infection is rare from any exposure of two days or less. Persons not getting a rash within several weeks of a deer tick bite do not need treatment unless they develop other signs such as arthritis (very rare).

Lyme Disease Vaccination

A vaccine for Lyme disease was approved for use by the FDA in 1998. Initial trials showed it was 80% effective in reducing the risk of Lyme disease in those people who received three doses over one year. The vaccine is approved for persons aged 15 to 70 years and is administered at 0, 1 and twelve months (e.g., January, February and January the following year) for a complete series. Antibody levels fall within one year, although the effect on immunity is not known.

There is some concern about the long-term safety of the Lyme vaccine, particularly regarding the possible association with subsequent arthritis in a subset of recipients. Over 440,000 Americans have received at least one dose of the vaccine. The FDA continues to investigate reports of Lyme disease and arthritis in people having received the vaccine. The vaccine may also cause muscle aches, fever, chills and injection site soreness for several days.

According to the American Academy of Family Physicians, vaccination against Lyme disease is recommended for persons of age 15 years who are at high risk for infection including those who:

"Reside, work or recreate in areas of high or moderate risk during Lyme transmission season.
Engage in activities (e.g., recreational, property maintenance, occupational, leisure) that result in frequent or prolonged exposure to tick infested habitat."
The Centers for Disease Control and Prevention have similar recommendations for people who meet both criteria above. Most others should not be considered for receiving the vaccine. The vaccine series should be started in the early spring, before the Lyme disease season begins. The complete review by the Advisory Committee on Immunization Practices is available.

Summary

Lyme disease is a preventable disease caused by a bacteria transmitted to humans by deer tick bites. Avoidance of ticks or removal of ticks within 48 hours minimizes the risk of disease. Vaccination may further reduce the risk of disease in some high risk individuals. Treatment of the disease in early phases is simple, inexpensive and effective. Awareness of risks and symptoms is the key to early treatment. Treatment of early disease generally does not impact a pilotís medical certificate status. Delays in recognition and treatment may cause long term complications and is difficult to treat. FAA medical status may be adversely affected by the manifestations of early or late systemic Lyme disease.