Lyme disease is the most common vector-borne illness in the United States. The condition is caused by the bacterium Borrelia burgdorferi, a spirochete transmitted to humans through the bite of infected blacklegged ticks (Ixodes scapularis). If left untreated, the bacterial infection can spread throughout the body, potentially leading to complications affecting the joints, heart, and nervous system. The question of whether a person can contract Lyme disease more than once depends on the body’s immune response and the ongoing threat of exposure.
Why Immunity Does Not Protect Against Reinfection
A person can contract Lyme disease multiple times because the body’s initial immune response is not sterilizing. When the Borrelia bacteria first enter the human host, the immune system develops antibodies, but these defenses do not confer lifelong protection against subsequent exposures. The antibodies created after one infection are generally insufficient to block a new infection acquired from a different tick bite later on.
The central reason for this lack of protective memory lies in the bacteria’s sophisticated immune evasion tactics, particularly a process known as antigenic variation. Borrelia burgdorferi can rapidly change its surface proteins, or antigens, which are the parts of the bacteria that the immune system recognizes. The bacteria possess a specialized genetic system that allows them to generate numerous variations of a surface lipoprotein during infection. This constant switching of its external appearance means that the immune system is always playing catch-up.
The antibodies generated against one version of the bacteria may not recognize the next variant. The bacteria also employ other strategies to survive the host response, such as inhibiting the complement system, a part of the innate immune defense. This ability to evade a full and effective immune clearance means the body does not develop the robust, long-term immunity needed to prevent a future infection. Any new bite from an infected tick can transmit a new strain of Borrelia, leading to a true reinfection.
Telling the Difference Between Relapse and New Infection
When symptoms return after initial treatment, it can be confusing to determine if the patient has a true reinfection or is experiencing persistent symptoms from the first episode. A true reinfection requires a new exposure to an infected tick, often occurring in a subsequent tick season. When a reinfection occurs, clinicians can often identify a new onset of symptoms, such as a second expanding rash at a different body site. Studies have genetically analyzed the Borrelia strains from recurrent cases and shown that the second strain is almost always a different genotype than the first.
By contrast, persistent or recurrent symptoms are often referred to as Post-Treatment Lyme Disease Syndrome (PTLDS) and are not considered a new infection. PTLDS involves symptoms like fatigue, generalized pain, and cognitive issues that linger or return months after the initial infection was treated with antibiotics. The cause of PTLDS is not fully understood, but it is thought to be a consequence of the initial infection, possibly involving an ongoing post-inflammatory process.
Some research suggests that Borrelia bacteria may form dormant “persister” cells or protective communities called biofilms, which could shield them from antibiotics. This could potentially lead to a true relapse of the original infection. However, the current consensus is that recurrent episodes of the rash and acute illness are new infections. Distinguishing the two scenarios relies heavily on a patient’s medical history, including evidence of a new tick bite, the timing of the symptoms, and clinical laboratory testing.
Steps to Prevent Future Lyme Disease
Since prior infection does not guarantee protection, the most effective strategy against getting Lyme disease multiple times is to focus on preventing tick bites altogether. When spending time outdoors in wooded or grassy areas, several steps can significantly reduce risk:
- Wear permethrin-treated clothing.
- Apply repellents containing DEET or picaridin to exposed skin.
- Tuck pants into socks and wear long-sleeved shirts to create a physical barrier against ticks.
- Perform a thorough full-body tick check after returning indoors.
- Examine clothing and pets for ticks.
Ticks must typically be attached for 36 to 48 hours to transmit the Borrelia bacterium, so prompt removal is highly protective. If a tick is found, it should be removed immediately using fine-tipped tweezers. Grasp the tick as close to the skin’s surface as possible and pull upward with steady, even pressure. Following removal, the bite area should be cleaned with soap and water or an antiseptic.