Medical Glossary

Searchable reference of medical, epidemiological, and public health terms used throughout InvisibleSignal

45 terms across 20 sections

A2 terms

Alpha-Gal Syndrome

An allergic condition triggered by the bite of the Lone Star tick (Amblyomma americanum) that causes sensitization to alpha-gal, a sugar molecule found in most mammalian meat. Reactions include hives, gastrointestinal distress, and anaphylaxis, typically occurring 3-6 hours after consuming red meat or dairy.

Related:Tick-Borne DiseaseMast Cell Activation Syndrome

Anaplasmosis

A tick-borne bacterial disease caused by Anaplasma phagocytophilum. It infects white blood cells and can cause fever, headache, muscle pain, and in severe cases organ failure. Transmitted primarily by Ixodes scapularis (blacklegged tick).

Related:Lyme diseaseEhrlichiosisVector-borne

B2 terms

Babesiosis

A tick-borne parasitic infection of red blood cells caused by Babesia microti. Symptoms range from asymptomatic to severe hemolytic anemia. It is particularly dangerous for immunocompromised and asplenic individuals.

Related:Lyme diseaseAnaplasmosisVector-borne

Borrelia burgdorferi

The spirochete bacterium that causes Lyme disease in North America. It is transmitted to humans through the bite of infected Ixodes ticks. The organism can disseminate to joints, heart, and nervous system if untreated.

Related:Lyme diseaseErythema migransWestern blot

C3 terms

Case Fatality Rate (CFR)

The proportion of people diagnosed with a disease who die from that disease within a specified time period. CFR = (deaths / confirmed cases) x 100. It is distinct from mortality rate, which uses the general population as the denominator.

Related:IncidencePrevalenceSurveillance

Coinfection

The simultaneous infection of a host by multiple pathogen species. Ticks can transmit multiple pathogens in a single bite, leading to coinfections (e.g., Lyme + babesiosis + anaplasmosis) that are more clinically severe and harder to diagnose and treat than single infections.

Related:BabesiosisAnaplasmosisLyme disease

Comorbidity

The simultaneous presence of two or more diseases or medical conditions in a patient. Comorbidities can complicate diagnosis, treatment, and prognosis. Tick-borne illness patients frequently present with multiple co-infections.

Related:Distinguishing diagnosesPTLDS

D3 terms

Diagnostic Delay

The time between symptom onset and confirmed diagnosis. For invisible illnesses like Lyme disease, ME/CFS, and fibromyalgia, diagnostic delays of months to years are common due to nonspecific symptoms, limited provider awareness, and inadequate testing.

Related:UnderreportingHealth equityDistinguishing diagnoses

Distinguishing Diagnoses

The systematic process of distinguishing a particular disease from others that present with similar clinical features. For tick-borne and invisible illnesses, clinicians must often consider a broad range of autoimmune, neurological, and psychiatric conditions.

Related:ComorbiditySerologyICD-10

Dysautonomia

A group of conditions caused by dysfunction of the autonomic nervous system, which controls involuntary functions such as heart rate, blood pressure, digestion, and temperature regulation. Common in post-infectious syndromes.

Related:POTSSmall Fiber NeuropathyME/CFS

E5 terms

Ehrlichiosis

A group of tick-borne bacterial infections caused by Ehrlichia species. Symptoms include fever, headache, fatigue, and muscle aches. It can be life-threatening if not treated promptly with doxycycline.

Related:AnaplasmosisLyme diseaseVector-borne

ELISA (Enzyme-Linked Immunosorbent Assay)

A plate-based immunoassay used as the first step in the CDC-recommended two-tier testing for Lyme disease. It detects antibodies (IgM and IgG) against Borrelia burgdorferi. A positive or equivocal result requires confirmation by Western blot.

Related:Western blotSerologyBorrelia burgdorferi

Endemic

The constant or usual presence of a disease within a given geographic area or population. Lyme disease is endemic in the northeastern and upper midwestern United States, where tick populations and reservoir hosts are established.

Related:EpidemicPrevalenceSurveillance

Epidemic

An increase in the number of cases of a disease above what is normally expected in a given population, area, or season. An epidemic can be localized or widespread and may signal emerging threats or surveillance gaps.

Related:EndemicIncidenceSurveillance

Erythema Migrans

The characteristic expanding red rash (often called a "bull's-eye" rash) that appears at the site of a tick bite in approximately 70-80% of Lyme disease cases. It typically appears 3-30 days after infection and is considered diagnostic without laboratory confirmation.

Related:Lyme diseaseBorrelia burgdorferi

F1 term

Fibromyalgia

A chronic condition characterized by widespread musculoskeletal pain, fatigue, sleep disturbances, and cognitive difficulties ("fibro fog"). It is classified as an invisible illness because patients often appear healthy despite significant functional impairment.

Related:ME/CFSPTLDSInvisible illness

H2 terms

Health Equity

The principle that everyone should have a fair and just opportunity to attain their highest level of health. Health inequities in tick-borne and invisible illness care are driven by geographic access, insurance status, provider awareness, and socioeconomic factors.

Related:Social determinants of healthHPSAUnderreporting

HPSA (Health Professional Shortage Area)

A designation by the Health Resources and Services Administration (HRSA) indicating a geographic area, population, or facility with a shortage of primary care, dental, or mental health providers. HPSAs correlate with higher diagnostic delays for tick-borne diseases.

Related:Health equityDiagnostic delayUnderreporting

I3 terms

ICD-10 (International Classification of Diseases, 10th Revision)

The World Health Organization's standardized coding system for diseases, symptoms, and procedures. Lyme disease codes include A69.20 (unspecified), A69.21 (meningitis), A69.22 (other cranial neuritis), and A69.23 (arthritis). Accurate coding is essential for surveillance and reimbursement.

Related:SurveillanceDistinguishing diagnosesUnderreporting

Incidence

The number of new cases of a disease occurring in a specified population during a defined time period. Incidence rate = new cases / population at risk. The CDC estimates approximately 476,000 new cases of Lyme disease annually in the United States.

Related:PrevalenceSurveillanceCase Fatality Rate

Invisible Illness

A broad term for any medical condition that is not outwardly visible to others. Includes chronic Lyme disease, ME/CFS, fibromyalgia, POTS, and many autoimmune conditions. Patients often face disbelief, stigma, and barriers to care because they "don't look sick."

Related:ME/CFSFibromyalgiaPOTSDiagnostic delay

J1 term

Jarisch-Herxheimer Reaction

A temporary worsening of symptoms that can occur within hours of starting antibiotic treatment for spirochetal infections like Lyme disease. It is caused by the release of toxins from dying bacteria and typically resolves within 24-48 hours. It is not an allergic reaction to the medication.

Related:Lyme diseaseBorrelia burgdorferi

L2 terms

Long COVID

A condition in which symptoms persist for weeks, months, or years after initial SARS-CoV-2 infection. Shares significant clinical overlap with ME/CFS and post-treatment Lyme disease. Symptoms include fatigue, cognitive impairment, dysautonomia, and exercise intolerance.

Related:ME/CFSPTLDSDysautonomia

Lyme Disease

The most common vector-borne disease in the United States, caused by the spirochete Borrelia burgdorferi and transmitted by Ixodes ticks. It can affect the skin, joints, heart, and nervous system. Early treatment with antibiotics is highly effective, but delayed diagnosis can lead to chronic complications.

Related:Borrelia burgdorferiErythema migransPTLDS

M2 terms

Mast Cell Activation Syndrome (MCAS)

A condition in which mast cells inappropriately release chemical mediators, causing symptoms across multiple organ systems including flushing, hives, gastrointestinal distress, tachycardia, and anaphylaxis. It is increasingly recognized in post-infectious and invisible illness populations.

Related:POTSDysautonomiaME/CFS

ME/CFS (Myalgic Encephalomyelitis / Chronic Fatigue Syndrome)

A complex, chronic, multi-system disease characterized by profound fatigue not improved by rest, post-exertional malaise (PEM), unrefreshing sleep, cognitive impairment, and orthostatic intolerance. It affects an estimated 836,000 to 2.5 million Americans.

Related:FibromyalgiaLong COVIDPTLDSDysautonomia

N2 terms

Neuroborreliosis

Neurological complications of Lyme disease caused by Borrelia burgdorferi infection of the nervous system. Manifestations include lymphocytic meningitis, cranial neuropathy (especially facial nerve palsy), radiculopathy, and encephalomyelitis. It occurs in approximately 10-15% of untreated Lyme disease cases.

Related:Lyme diseaseBorrelia burgdorferiPTLDS

Nymph

The juvenile stage of a tick's life cycle, between larva and adult. Nymphs are responsible for the majority of Lyme disease transmission because of their tiny size (poppy seed-sized), making them difficult to detect on the body. They are most active in late spring and summer.

Related:Lyme diseaseVector-borneTick-Borne Disease

P5 terms

PCR (Polymerase Chain Reaction)

A molecular diagnostic technique that amplifies specific DNA sequences to detect the presence of a pathogen. In tick-borne disease, PCR can identify Borrelia, Babesia, Anaplasma, and Ehrlichia DNA directly from blood or tissue samples. It is highly specific but sensitivity varies by specimen type and timing.

Related:ELISAWestern blotSerology

Post-Treatment Lyme Disease Syndrome (PTLDS)

A condition affecting approximately 10-20% of Lyme disease patients who continue to experience symptoms such as fatigue, pain, and cognitive difficulties after completing standard antibiotic treatment. The underlying mechanisms remain under active research.

Related:Lyme diseaseME/CFSDiagnostic delay

POTS (Postural Orthostatic Tachycardia Syndrome)

A form of dysautonomia characterized by an excessive increase in heart rate (30+ bpm) upon standing, accompanied by lightheadedness, palpitations, exercise intolerance, and fatigue. It is frequently comorbid with Lyme disease, ME/CFS, and Long COVID.

Related:DysautonomiaME/CFSLong COVID

Prevalence

The total number of existing cases of a disease in a given population at a specific point in time (point prevalence) or over a period (period prevalence). Unlike incidence, prevalence includes both new and pre-existing cases.

Related:IncidenceSeroprevalenceSurveillance

Prophylaxis

A preventive medical treatment administered after a potential exposure to disease. For Lyme disease, a single 200mg dose of doxycycline within 72 hours of a tick bite in endemic areas is recommended as prophylaxis by the IDSA when specific criteria are met.

Related:Lyme diseaseTick-Borne DiseaseEndemic

R1 term

RMSF (Rocky Mountain Spotted Fever)

A severe, potentially fatal tick-borne disease caused by Rickettsia rickettsii. Symptoms include sudden fever, headache, and a characteristic spotted rash. It is the most lethal rickettsial disease in the Americas and requires immediate treatment with doxycycline.

Related:EhrlichiosisVector-borneCase Fatality Rate

S5 terms

Serology

The scientific study and diagnostic use of blood serum, particularly antibodies. Serological testing is the primary laboratory method for diagnosing Lyme disease, using the CDC-recommended two-tier approach (ELISA followed by Western blot or modified two-tier testing).

Related:ELISAWestern blotPCR

Seroprevalence

The proportion of a population that tests positive for antibodies against a specific pathogen, indicating past or current infection. Seroprevalence studies suggest that Lyme disease is far more common than case-based surveillance indicates.

Related:PrevalenceSerologyUnderreporting

Small Fiber Neuropathy

A condition involving damage to the small nerve fibers in the skin and organs, causing burning pain, tingling, numbness, and autonomic dysfunction. It has been documented in patients with Lyme disease, fibromyalgia, and other post-infectious conditions, and is diagnosed via skin biopsy.

Related:DysautonomiaFibromyalgiaPTLDS

Social Determinants of Health

The conditions in which people are born, grow, work, live, and age that affect health outcomes. For tick-borne and invisible illnesses, determinants include geographic location, access to knowledgeable providers, insurance coverage, socioeconomic status, and environmental exposure risk.

Related:Health equityHPSADiagnostic delay

Surveillance

The ongoing systematic collection, analysis, and interpretation of health-related data essential for planning, implementation, and evaluation of public health practice. CDC ArboNET is the national surveillance system for tick-borne diseases in the United States.

Related:IncidencePrevalenceUnderreporting

T2 terms

Tick-Borne Disease

Any disease transmitted to humans through the bite of an infected tick. In the United States, this includes Lyme disease, babesiosis, anaplasmosis, ehrlichiosis, RMSF, tularemia, Powassan virus, and alpha-gal syndrome. The number of tick-borne disease cases has more than doubled since 2004.

Related:Vector-borneLyme diseaseSurveillance

Two-Tier Testing

The CDC-recommended algorithm for laboratory diagnosis of Lyme disease. The standard approach uses an ELISA as the first tier, followed by a Western blot (IgM and/or IgG) for confirmation. A modified two-tier approach using two ELISAs has been endorsed since 2019.

Related:ELISAWestern blotSerology

U1 term

Underreporting

The systematic failure to capture all cases of a disease in surveillance data. The CDC estimates that actual Lyme disease cases are approximately 10 times higher than reported cases, suggesting that only about 10% of infections are captured through standard surveillance.

Related:SurveillanceDiagnostic delayHealth equity

V1 term

Vector-Borne Disease

An infectious disease transmitted to humans by blood-feeding arthropods such as ticks, mosquitoes, and fleas. Vector-borne diseases account for more than 17% of all infectious diseases globally. Climate change is expanding the geographic range of many disease vectors.

Related:Tick-Borne DiseaseEndemicSurveillance

W1 term

Western Blot

An immunoassay technique used as the confirmatory second tier in Lyme disease testing. It detects antibodies against specific Borrelia burgdorferi proteins (bands). A positive IgM requires 2 of 3 specified bands; a positive IgG requires 5 of 10 specified bands.

Related:ELISASerologyTwo-Tier Testing

Z1 term

Zoonotic Disease

An infectious disease that has jumped from a non-human animal to humans. Most tick-borne diseases are zoonotic, with wildlife reservoirs (white-footed mice, deer, birds) maintaining the pathogen in nature. Understanding zoonotic transmission cycles is critical for prevention strategies.

Related:Vector-borneTick-Borne DiseaseSurveillance

This glossary is provided for educational purposes and health literacy. It is not a substitute for professional medical advice, diagnosis, or treatment. Sources include CDC, NIH, WHO, and peer-reviewed medical literature.

Medical Glossary

Searchable reference of medical, epidemiological, and public health terms used throughout InvisibleSignal

45 terms across 20 sections

A2 terms

Alpha-Gal Syndrome

Related:Tick-Borne DiseaseMast Cell Activation Syndrome

Anaplasmosis

Related:Lyme diseaseEhrlichiosisVector-borne

B2 terms

Babesiosis

Related:Lyme diseaseAnaplasmosisVector-borne

Borrelia burgdorferi

Related:Lyme diseaseErythema migransWestern blot

C3 terms

Case Fatality Rate (CFR)

Related:IncidencePrevalenceSurveillance

Coinfection

Related:BabesiosisAnaplasmosisLyme disease

Comorbidity

Related:Distinguishing diagnosesPTLDS

D3 terms

Diagnostic Delay

Related:UnderreportingHealth equityDistinguishing diagnoses

Distinguishing Diagnoses

Related:ComorbiditySerologyICD-10

Dysautonomia

Related:POTSSmall Fiber NeuropathyME/CFS

E5 terms

Ehrlichiosis

Related:AnaplasmosisLyme diseaseVector-borne

ELISA (Enzyme-Linked Immunosorbent Assay)

Related:Western blotSerologyBorrelia burgdorferi

Endemic

Related:EpidemicPrevalenceSurveillance

Epidemic

Related:EndemicIncidenceSurveillance

Erythema Migrans

Related:Lyme diseaseBorrelia burgdorferi

F1 term

Fibromyalgia

Related:ME/CFSPTLDSInvisible illness

H2 terms

Health Equity

Related:Social determinants of healthHPSAUnderreporting

HPSA (Health Professional Shortage Area)

Related:Health equityDiagnostic delayUnderreporting

I3 terms

ICD-10 (International Classification of Diseases, 10th Revision)

Related:SurveillanceDistinguishing diagnosesUnderreporting

Incidence

Related:PrevalenceSurveillanceCase Fatality Rate

Invisible Illness

Related:ME/CFSFibromyalgiaPOTSDiagnostic delay

J1 term

Jarisch-Herxheimer Reaction

Related:Lyme diseaseBorrelia burgdorferi

L2 terms

Long COVID

Related:ME/CFSPTLDSDysautonomia

Lyme Disease

Related:Borrelia burgdorferiErythema migransPTLDS

M2 terms

Mast Cell Activation Syndrome (MCAS)

Related:POTSDysautonomiaME/CFS

ME/CFS (Myalgic Encephalomyelitis / Chronic Fatigue Syndrome)

Related:FibromyalgiaLong COVIDPTLDSDysautonomia

N2 terms

Neuroborreliosis

Related:Lyme diseaseBorrelia burgdorferiPTLDS

Nymph

Related:Lyme diseaseVector-borneTick-Borne Disease

P5 terms

PCR (Polymerase Chain Reaction)

Related:ELISAWestern blotSerology

Post-Treatment Lyme Disease Syndrome (PTLDS)

Related:Lyme diseaseME/CFSDiagnostic delay

POTS (Postural Orthostatic Tachycardia Syndrome)

Related:DysautonomiaME/CFSLong COVID

Prevalence

Related:IncidenceSeroprevalenceSurveillance

Prophylaxis

Related:Lyme diseaseTick-Borne DiseaseEndemic

R1 term

RMSF (Rocky Mountain Spotted Fever)

Related:EhrlichiosisVector-borneCase Fatality Rate

S5 terms

Serology

Related:ELISAWestern blotPCR

Seroprevalence

Related:PrevalenceSerologyUnderreporting

Small Fiber Neuropathy

Related:DysautonomiaFibromyalgiaPTLDS

Social Determinants of Health

Related:Health equityHPSADiagnostic delay

Surveillance

Related:IncidencePrevalenceUnderreporting

T2 terms

Tick-Borne Disease

Related:Vector-borneLyme diseaseSurveillance

Two-Tier Testing

Related:ELISAWestern blotSerology

U1 term

Underreporting

Related:SurveillanceDiagnostic delayHealth equity

V1 term

Vector-Borne Disease

Related:Tick-Borne DiseaseEndemicSurveillance

W1 term

Western Blot

Related:ELISASerologyTwo-Tier Testing

Z1 term

Zoonotic Disease

Related:Vector-borneTick-Borne DiseaseSurveillance