What is Lyme disease?
Lyme disease is an infection caused by the bacteria Borrelia burgdorferi. It is spread by deer ticks (also known as black-legged ticks) infected with the disease. These tiny ticks are the size of a poppy seed or the head of a pin, and are much smaller than dog ticks, which are the size of a pencil eraser or watermelon seed.
How is Lyme disease diagnosed?
If you have been bitten by a tick or have symptoms commonly seen in Lyme disease, it’s possible that you have Lyme disease. Early Lyme disease is diagnosed without a blood test. If you have the distinctive expanding circular rash (“bull's eye”) at the site of a tick bite, you likely have early Lyme disease. This is easy to treat with antibiotics. Four out of 5 people who are infected with Lyme develop this rash, usually within a few days.
When the rash does not appear or your symptoms don’t show until weeks or months after you were bitten, diagnosis can be more difficult. This is because other symptoms, including headache, joint aches, or fever, can look like other illnesses. A blood test can be helpful in making the diagnosis.
What is the blood test for Lyme disease?
The blood test for Lyme disease looks for signs that antibodies (substances in the blood that fight bacteria) are forming against the Lyme bacteria. Lyme antibodies usually take at least 5-6 weeks to develop, which is why a blood test doesn’t help early in the disease. Later on, blood tests can be very useful.
The most common blood test for Lyme is the ELISA (enzyme-linked immunosorbent assay). If the results of this test are abnormal, then a Western blot test is usually done to confirm results. Together, these tests are very sensitive.
How do ticks give people Lyme disease?
Ticks usually crawl around your body for quite a while before biting you. It must be attached to your skin for at least 36 hours before it can transmit the bacteria that causes Lyme disease.
Not every deer tick carries Lyme disease, and most people who are bitten by infected ticks do not develop Lyme disease. According to the US Centers for Disease Control, only 1-5% of people who get bitten by a deer tick develop Lyme disease.
I was bitten by a deer tick, what should I do?
Finding and removing the tick early is the best thing you can do to reduce your risk.
- If you are sure that the tick was attached for less than 24 hours, you don’t need to do anything.
- If you are not sure how long the tick was attached, know that it was on for over 48-72 hours, or if the tick is engorged (full of blood), you have 2 options. Both are safe and recommended, so it’s your choice:
- Preventive antibiotic: Talk with your clinician about whether taking a single dose of antibiotics within 72 hours of finding the tick is appropriate to lower your risk of infection.
- Observation: Watch the site of the bite for signs of a rash, and pay attention to any flu-like symptoms. Take antibiotics only if you develop early Lyme.
- If you see a bull's eye rash on your skin, there is no need for testing. You should begin treatment. Testing is not necessary because results would most likely be negative this early in the disease.
- If you have symptoms of a flu-like illness but no rash, talk to your clinician to help decide about treatment. Testing won't help, as it’s usually negative early in the disease. Your physical exam and tick exposure are enough to guide your doctor's diagnosis.
I have muscle aches and joint pain, and I am always tired. Could these be signs of Lyme disease? Would a test help me find out?
These symptoms—joint pain, muscle pain, fatigue, weakness or numbness in the arms and legs—could be signs of Lyme disease. But, they could also be caused by much more common illnesses.
Testing makes sense if you have risk factors for Lyme disease (i.e., you live in a high-risk area, which includes all of Massachusetts, or you spend lots of time in the woods) and your doctor suspects that your symptoms may suggest Lyme disease. Blood tests can be helpful in diagnosing later stages of Lyme disease.
PHOTO (from left to right): The deer tick (Ixodes scapularis) adult female, adult male, nymph, and larva on a centimeter scale. (CDC web site)
---------------------------------. This document is not a substitute for your care team's medical advice and should not be relied upon for treatment of specific medical conditions. Source: This content of this article is produced by MGH/PCOI. MGH patients can find this in the Resources section of Patient Gateway, under Partners Care Advice (PCOI), along with patient handout about many other health & wellness topics.