Quick Answer
The chances of getting Lyme disease from a tick bite vary based on the type of tick, where you were bitten, and how long the tick was attached. Studies show that in highly Lyme disease endemic areas, about 1 in 5 deer tick bites leads to Lyme disease. The risk is much lower if the tick is not a deer tick or if it was attached for less than 36 hours. Promptly removing ticks and watching for symptoms can prevent most cases of Lyme disease.
What is Lyme Disease?
Lyme disease is an infectious disease caused by the bacterium Borrelia burgdorferi. It is transmitted to humans through the bite of infected ticks, usually blacklegged ticks (also known as deer ticks). The most common symptoms of Lyme disease include fever, headache, fatigue, and a skin rash called erythema migrans. If left untreated, the infection can spread to the joints, heart, and nervous system. Lyme disease is diagnosed based on symptoms, physical findings (such as rash), and laboratory testing. Most cases can be successfully treated with antibiotics, especially if treatment is started early.
Chances of Getting Lyme Disease from a Tick Bite
Not all tick bites result in Lyme disease. The chances of getting Lyme disease from a tick bite depend on these factors:
Type of tick: In the U.S., only blacklegged ticks (deer ticks) transmit Lyme disease. Other types of ticks, such as dog ticks and lone star ticks, do not carry or transmit the Lyme disease bacterium. Deer ticks are found mostly in the northeastern, mid-Atlantic, and north-central states.
Geographic location: Lyme disease exposure occurs in areas where infected ticks are endemic. The risk is higher if you are bitten in an area known to have a high rate of infected ticks. In the U.S., 95% of Lyme disease cases are reported from just 14 states in the Northeast, mid-Atlantic, and upper Midwest.
Length of tick attachment: Ticks must be attached for 36-48 hours to transmit Lyme disease. The longer an infected tick stays attached, the higher the risk of transmission. Promptly finding and removing ticks reduces the chances of getting Lyme.
Stage of tick: Nymphal deer ticks are more likely to transmit Lyme than adult ticks because their small size makes them harder to detect and remove. Nymphs are most active during spring and early summer.
Infection Rates in Tick Populations
Studies have found the following average infection rates among deer ticks:
- Nymphal deer ticks: 18-24% infected in high incidence Lyme areas
- Adult deer ticks: 20-25% infected in high incidence areas
- Less than 1% infected in low incidence western U.S. areas
Based on the infection rate, the estimated risk of getting Lyme disease from an observed deer tick bite is:
1 in 5 bites in high incidence regions (Northeast, mid-Atlantic)
1 in 10 bites in low incidence regions (Western U.S.)
However, 10-30% of Lyme disease patients do not recall getting bitten by a tick. This suggests the actual risk per bite may be higher.
Factors That Increase or Decrease Risk
Some factors can increase or decrease the odds of a tick bite leading to Lyme disease:
Increased risk
- Tick bite during spring or summer when nymphs are most active
- Delayed tick removal (over 36 hours)
- Multiple tick bites in an endemic area
- Tick found to be infected with Lyme (positive PCR test)
Decreased risk
- Prompt tick removal (within 24 hours)
- No tick engorgement or minimal engorgement
- Negative tick lab test for Lyme
- Tick bite prevention measures (repellent, daily checks)
Symptoms and Diagnosis of Lyme Disease
If a tick bite occurs, watch for signs and symptoms of Lyme disease which typically begin 3 to 30 days after you are bitten:
- Erythema migrans rash (70-80% of cases)
- Flu-like illness – fatigue, fever, chills, muscle aches, joint pain, headache
- Neurologic symptoms – facial palsy, meningitis, neuropathy
- Arthritis – swollen, painful knees and other large joints
- Cardiac symptoms – heart palpitations, lightheadedness
See your healthcare provider if any of these develop after a tick bite. Lyme disease is diagnosed based on symptoms, physical exam findings, medical history (tick bite), and lab tests. Blood tests can detect antibodies to Lyme disease bacteria, although results may be negative early in infection. PCR direct detection of Lyme DNA may also be done on synovial fluid or skin biopsies.
Reducing Risk of Lyme Disease after Tick Bite
These precautions can help prevent Lyme disease transmission after known or suspected tick bites:
- Remove embedded ticks promptly using fine-tipped tweezers. Do not twist or squeeze the ticks during removal.
- Wash bite area thoroughly with soap and water after tick removal.
- Watch for signs and symptoms of Lyme for 30 days.
- Consider a single dose prophylactic antibiotic if tick had significant attachment in a highly Lyme endemic area. This should be started within 72 hours of tick removal.
- Have an experienced healthcare provider check for any remaining tick mouth parts in the skin.
- Identify the tick if possible to assess Lyme disease risk based on type of tick and endemic area. You can submit a photo of the tick to online databases for identification.
- Contact your doctor to discuss antibody testing of the tick itself for Lyme bacteria. This PCR lab test can determine if the tick was infected.
With early tick removal, monitoring, and preventive antibiotics when appropriate, most people can avoid developing a Lyme disease infection after a recognized tick bite.
Conclusion
The chances of getting Lyme disease from a single deer tick bite in endemic areas is estimated to be approximately 1 in 5, although this risk estimate varies based on geographic location and individual circumstances. Promptly finding and removing attached ticks reduces the risk significantly. Watch for symptoms for 30 days after tick removal and see a medical provider if any signs suggestive of Lyme disease develop. Appropriate use of antibiotics and close follow-up after tick bites can prevent most cases of Lyme disease. People should use tick repellents, do thorough tick checks after outdoor activities in endemic areas, and learn proper tick removal techniques to prevent Lyme disease transmission.