Lyme

Transmission

Lyme disease is a vector-borne illness spread through the bite of infected ticks (the blacklegged tick in the northeastern, mid-Atlantic, and north-central United States and the western blacklegged on the Pacific coast). Ticks may attach to the body anywhere, but are often found in the armpit, groin and scalp. Lyme disease is usually transmitted only after the tick has been attached for 36 hours or more.

Immature tick “nymphs” are responsible for most human cases of Lyme disease. While adult ticks may spread Lyme disease, they are large enough to be spotted and removed before Lyme can be contracted. Nymphs are much smaller (less than 2 mm) and may go unnoticed. Nymphs are most active during spring and summer months, when Lyme disease is most commonly contracted.

Signs and symptoms

Early Signs and Symptoms (< 30 days after tick bite)

• Erythema migrans (EM) rash:
  • Known as a “bulls-eye” rash
  • Occurs in majority of Lyme cases
  • Appears at the site of the tick bite a few days or weeks after the bite
  • Expands gradually and grow to 12 inches or more
  • Rarely itchy or painful
  
  
• Fever, chills, headache, fatigue, muscle and joint aches, and swollen lymph nodes

Later Signs and Symptoms (days to months after tick bite)

• Severe headaches and neck stiffness
• EM rashes on other areas of the body
• Severe joint pain and swelling
• Facial palsy (loss of muscle tone or droop on one or both sides of the face)
• Intermittent pain in tendons, muscles, joints, and bones
• Heart palpitations or an irregular heart beat (Lyme carditis)
• Episodes of dizziness or shortness of breath
• Inflammation of the brain and spinal cord
• Nerve pain
• Shooting pains, numbness, or tingling in the hands or feet
• Problems with short-term memory

Lyme bacteria

Lyme disease in the United States is caused by a bacteria called Borrelia burgdorferi. Borrelia burgdorferi is a flexible, spiral-shaped bacteria called a spirochete. Borrelia burgdorferi does not produce toxins, unlike most disease-causing bacteria. Instead, it interacts directly with the cells it infects.

Prevention

To prevent Lyme disease, the CDC recommends:

• Avoiding areas likely to have ticks
• Using insect repellent on skin and clothing
• Showering as soon as possible after potentially being exposed to ticks
• Inspecting your body for ticks and remove them promptly
• Inspecting pets and equipment for ticks and removing them
• Heat-treating clothing that may have been exposed to ticks by placing dry clothing in the dryer on high for 10 minutes or by washing clothing and drying in a dryer until completely dry and warm

Diagnosis

Lyme disease is diagnosed based on symptoms, the possibility of exposure to infected ticks and laboratory testing. Laboratory tests that detect IgG and IgM antibodies produced in response to the Lyme bacteria help further confirm whether a person has been exposed to Borrelia burgdorferi.

To help ensure accurate diagnosis and effective treatment, the CDC recommends a two-tiered testing method for Lyme disease. A first tier test is conducted using a fluorescent immunoassay (FIA), enzyme immunoassay (EIA), or indirect immunofluorescence assay (IFA). False positive results may occur due to the presence of other diseases or disorders, which evoke an antibody response that shares structural similarities to Lyme antibodies. First tier assays also have a lower specificity (high false positive rate), therefore, a positive first tier result is tested again using a second tier test called a Western Blot or an immunoblot. With an immunoblot, a lysate of the Borrelia burgdorferi bacteria is separated into its components using gel electrophoresis and bound to a membrane. The patient sample is then applied to the membrane. If the patient has been infected with Borrelia burgdorferi, their body will have produced antibodies that will bind to antigens on the membrane. A dye is then applied to identify the “bands” where the antibody has attached to the antigen. The most common type of immunoblot used in Lyme testing is the Western Blot. CDC guidelines dictate that IgM Western Blot is positive when at least two out of three bands are present and that IgG Western Blot is considered positive when at least five out of ten bands are present. Because of the low sensitivity and high specificity of immunoblot tests, both the first tier test and the second tier immunoblot test must be positive for a Lyme diagnosis to be made.

Treatment

If detected early, Lyme disease can be treated successfully with antibiotics.

Recommended Reading

http://www.cdc.gov/lyme

http://www.bayarealyme.org/about-lyme/what-causes-lyme-disease/borrelia-burgdorferi/

Brenner, C. Understanding the Western Blot. September, 1996.