Lyme Disease
Glossary
Medical terminology shouldn't be a barrier to understanding your own health. This glossary defines key Lyme disease terms in plain language — with links to related pages for deeper learning.
Use the alphabet links to navigate to a section. All definitions are reviewed by our Scientific Advisory Board.
A
- Anaplasmosis
- A tick-borne bacterial disease caused by Anaplasma phagocytophilum, transmitted by the same black-legged tick that spreads Lyme. Symptoms include fever, headache, muscle aches, and low blood counts. Treatable with doxycycline.
- Antibody
- A protein produced by the immune system in response to a specific pathogen. Lyme blood tests detect antibodies to Borrelia burgdorferi — not the bacteria itself. This is why tests can miss early infection before the immune response develops.
- Arthritis, Lyme
- Joint inflammation caused by Borrelia burgdorferi in later-stage disease, typically affecting large joints — especially the knees. Characterized by intermittent swelling and pain.
B
- Babesiosis
- A tick-borne parasitic infection of red blood cells, caused by Babesia microti and related species. Common Lyme co-infection. Ranges from mild to life-threatening. Does NOT respond to doxycycline — requires antiparasitic treatment.
- Bell's Palsy (Lyme-related)
- Weakness or paralysis on one side of the face caused by Lyme-related facial nerve inflammation. More common in children with Lyme than in adults. Generally responds to antibiotic treatment.
- Borrelia burgdorferi
- The primary spiral-shaped bacterium (spirochete) causing Lyme disease in North America. Transmitted through tick bites. Related species cause Lyme in Europe and Asia.
- Brain Fog
- Patient term for cognitive difficulties associated with Lyme disease — including trouble concentrating, memory lapses, and word-finding difficulty. Often reported in persistent Lyme symptoms.
C
- CDC Two-Tier Testing
- The CDC-recommended approach to Lyme blood testing: a first-tier ELISA test followed by a Western blot if the first tier is positive or indeterminate. Both must be positive for a serologic Lyme diagnosis.
- Co-infection
- Simultaneous infection with two or more pathogens. Ticks can transmit Lyme and other infections (e.g., anaplasmosis, babesiosis) in a single bite.
D
- Deer Tick
- Common name for Ixodes scapularis, the black-legged tick — the primary Lyme vector in eastern and central United States.
- Doxycycline
- First-line antibiotic treatment for early Lyme disease in adults and children over 8. Also treats several tick-borne co-infections.
E
- Ehrlichiosis
- Tick-borne bacterial disease caused by Ehrlichia species. Transmitted primarily by the lone star tick. Fever, headache, muscle aches. Treatable with doxycycline.
- ELISA (Enzyme-Linked Immunosorbent Assay)
- The first-tier Lyme blood test, detecting antibodies in the blood. Highly sensitive but can produce false positives. Must be followed by Western blot if positive.
- Erythema Migrans (EM)
- The expanding skin rash that is the hallmark early sign of Lyme disease. Appears at the tick bite site 3–30 days after the bite. Its presence alone is sufficient to diagnose Lyme — no lab testing needed.
L
- Lyme Carditis
- Cardiac inflammation caused by Lyme bacteria, producing heart rhythm abnormalities including varying degrees of heart block. Usually resolves with antibiotic treatment.
- Lyme Neuroborreliosis
- Neurological complications of Lyme disease: meningitis, encephalitis, cranial nerve palsies, peripheral neuropathy. Can occur in early disseminated and late stages.
N
- Nymph
- The second tick life stage — between larva and adult. Nymphs are the primary transmitters of Lyme to humans because they are tiny (1–2 mm, poppy seed size) and active during spring and early summer when people are outdoors.
P
- PTLDS (Post-Treatment Lyme Disease Syndrome)
- Persistent symptoms (fatigue, pain, cognitive difficulties) continuing after completing standard antibiotic treatment for Lyme disease. Affects ~10–20% of patients. Mechanisms under active research.
S
- Spirochete
- A bacterium with a spiral or corkscrew shape. Borrelia burgdorferi, the Lyme pathogen, is a spirochete. This shape enables movement through tissues and may contribute to immune evasion.
T
- Tick-Borne Disease
- Any illness transmitted through an infected tick bite. Common US examples: Lyme disease, anaplasmosis, babesiosis, ehrlichiosis, Rocky Mountain spotted fever, Powassan virus.
W
- Western Blot
- The confirmatory second-tier Lyme blood test. Identifies specific antibody bands against Lyme bacteria. A defined number of specific IgM or IgG bands must be positive for a confirmatory result.