Causes and Risk Factors of Lyme Disease

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Lyme disease is caused by an infection from the bacterium Borrelia burgdorferi. Humans may develop the disease after being bitten by an infected tick. According to the Centers for Disease Control and Prevention (CDC), Lyme disease cannot be transmitted sexually, or by kissing or drinking out of the same glass as someone who has Lyme disease. There are no reported instances of transmission from person to person or animal to person; it's transmitted only by ticks.

Lyme disease risk factors
Illustration by Joshua Seong. © Verywell, 2018. 

Ticks

You may not think that you're at risk for Lyme disease because of where you live. While most cases come from a particular set of states, the disease touches every part of the United States. And remember: Though your risk of a tick bite may be relatively low when you enter your backyard, it could most certainly go up when traveling or engaging in recreational activities.

Lifestyle Risk Factors

There are certain lifestyle risk factors associated with exposure to ticks and, thus, to the potential to contract Lyme disease. These include:

  • Being a hunter
  • Having pets
  • Living in a rural area
  • Living in, working in, or traveling to one of the tick hotspots in the United States (Northeast, Mid-Atlantic, or North-Central states)
  • Spending time in wooded or grassy areas
  • Having an outdoor occupation

There are also things you can do to prevent getting Lyme disease in the first place.

Genetics

While Lyme disease isn't genetic, you can inherit genes that make it more likely that you'll experience symptoms that are more severe should you contract Lyme disease. The greatest genetic association for Lyme disease is thought to be in certain variants of class II major histocompatibility complex (MHC) genes. MHC is located on the short arm of chromosome 6. It includes class I, II, and III MHC genes, each of which affect the immune system. Class II genes play a role in generating antigen-specific T cell responses.

There are specific class II HLA gene variants (genotypes)—HLA-DR4 and HLA-DR2—that have been linked to involvement in Lyme arthritis. It has been theorized that once the microorganism from a Lyme infection moves to the joints, the immune response against it cross-reacts with one's own joint tissue in people who have HLA-DR4 and HLA-DR2, leading to an autoimmune reaction and creating more severe arthritis.

People who have Lyme disease more severely and who do not respond well to antibiotic treatment are more often found to have the DRB1*0101 and 0401 class II genotypes, which also indicates an autoimmune reaction. Continued research is being done on the link between genes and Lyme disease.

Post-Treatment Lyme Disease Syndrome

After treatment, a small number of people will develop persistent symptoms, which some refer to as "chronic" Lyme disease. It's a contentious diagnosis. While the CDC acknowledges that certain symptoms can persist after treatment is completed (such as joint pain and neuropathy), those symptoms will almost universally resolve within six months or less. Beyond that time, there is little evidence that the persistent symptoms—most specifically chronic fatigue—are directly linked to persistent infection with Borrelia burgdorferi. For these individuals, the CDC has classified the illness as post-treatment Lyme disease syndrome (PTLDS). The CDC cautions against prolonged antibiotic therapy for the treatment of PTLDS.

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