Glossary
A Listener’s Guide to Long COVID, Related Illnesses, Treatments & Tools
Medical Terms (most commonly used)
Brain Fog: A term describing cognitive difficulties such as problems with focus, memory, processing speed, and mental clarity.
Covid-19: COVID-19 (Coronavirus Disease 2019) is a respiratory and systemic illness caused by the SARS-CoV-2 virus. While it initially presents with symptoms like fever, cough, and fatigue, it can affect multiple organ systems – including the lungs, heart, nervous system, and blood vessels. Disease severity ranges from asymptomatic or mild to life-threatening. COVID-19 can also trigger prolonged symptoms in some individuals, leading to post-acute conditions collectively known as Long COVID.
Dysautonomia/ Autonomic Dysfunction: A malfunction of the autonomic nervous system, affecting functions like heart rate, blood pressure, body temperature and digestion.
Exercise Intolerance: is the inability to perform physical activity at a level that's normal for your age and size. It commonly causes symptoms like shortness of breath, fatigue, muscle soreness or chest pain (angina).
Fibromyalgia: A disorder characterized by widespread musculoskeletal pain, fatigue, sleep disturbances, and cognitive issues.
Gastroparesis: A condition where the stomach's motility is impaired, leading to delayed emptying, nausea, vomiting, and bloating
Gut Dysbiosis: An imbalance in the gut microbiota, which can lead to digestive issues, inflammation, and other health problems.
Gut Microbiome: The gut microbiome refers to the trillions of microorganisms – primarily bacteria – that live in the digestive tract. These microbes support digestion, immune regulation, and communication with the brain via the gut-brain axis. Disruptions in this microbial balance, known as gut dysbiosis, have been linked to inflammation and immune dysfunction.
Histamine Intolerance: Happens when your body doesn't have enough enzymes (like DAO) to break down and metabolize dietary histamine. This can cause histamine to build up and trigger symptoms including headaches, fatigue, and gastrointestinal discomfort.
Long Covid: The WHO defines it as “the continuation or development of new symptoms 3 months after the initial SARS-CoV-2 infection, with these symptoms lasting for at least 2 months with no other explanation.” It is often also referred to as PASC, which stands for “Post-acute Sequelae of COVID”.
MCAS: Stands for “Mast Cell Activation Syndrome”. It is a condition where mast cells release excessive inflammatory mediators, leading to symptoms like hives, swelling, and gastrointestinal discomfort.
ME/CFS: Stands for “Myalgic Encephalomyelitis/Chronic Fatigue Syndrome”. It is a serious, multisystem illness that is often triggered by infections and marked by profound, disabling fatigue that is not improved by rest. ME/CFS affects the nervous, immune, and energy metabolism systems, and includes hallmark symptoms such as cognitive dysfunction ("brain fog"), unrefreshing sleep, and post-exertional malaise (PEM) – a worsening of symptoms following even minimal physical or mental effort. This condition significantly impairs daily functioning and quality of life.
Mitochondrial Dysfunction: Impaired function of the mitochondria, leading to decreased energy production and contributing to fatigue and other symptoms such as headaches or light and sound sensitivity.
Neuropathy: Damage or dysfunction of one or more nerves, resulting in numbness, tingling, muscle weakness, and pain in the affected area.
Orthostatic Intolerance: A condition where the body struggles to regulate blood pressure upon standing, leading to dizziness, lightheadedness, and fainting.
PEM: Stands for Post-Exertional Malaise. It is a worsening of symptoms following physical or mental exertion, often delayed and lasting for days or weeks. It is also often referred to as Post-Exertional Neuroimmune Exhaustion (PENE).
POTS: Stands for “Postural Orthostatic Tachycardia Syndrome”. It is a disorder of the autonomic nervous system characterized by a significant increase in heart rate when transitioning from lying down to standing up, leading to symptoms like dizziness, fainting, and fatigue.
SARS-CoV-2: SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) is the virus responsible for COVID-19. It is a novel coronavirus first identified in late 2019 and spreads primarily through respiratory droplets and aerosols. The virus enters human cells by binding to the ACE-2 receptor, which is found in many tissues throughout the body. This widespread receptor distribution may help explain the virus’s ability to affect multiple organ systems and contribute to long-term complications.
Tinnitus: The experience of ringing or other noises in one or both of your ears. The noise you hear when you have tinnitus isn't caused by an external sound, and other people can't hear it.
Medical Terms (more complex)
ACE2 receptors: Stands for “angiotensin-converting enzyme 2”. This is a protein that is on the surface of many cell types. Also an enzyme, it cuts up the larger protein angiotensinogen into smaller proteins that go on to regulate cell functions. The SARS-CoV-2 virus spike-like proteins on its surface bind to ACE2 like a key and a lock before entering and infecting a cell. Hence, ACE2 acts as a cellular doorway.
Blood-Brain Barrier: The endothelium inside your brain’s blood vessels – a protective layer of cells that line the inner surface of blood vessels in your brain, to defend against harmful substances, germs and other things that could cause damage.
Brain
Brainstem: The brainstem connects the brain to the spinal cord. Sitting at the bottom of the brain, it includes the midbrain, pons and medulla oblongata. The brainstem sends messages to the rest of the body to regulate balance, breathing, and other autonomic functions.
“Broken Bridge Syndrome” Hypothesis: Posits that structural disconnections between the brainstem and cerebellum contribute to Post Covid Syndrome symptomatology.
Cerebellum: The portion of the brain between the brainstem and the cerebrum. Controls balance and coordination for complex motor functions. The name “cerebellum” in Latin means “little brain.” Despite its size, it holds more than half of the neurons (cells that make up your nervous system) in the entire body.
Chemokines: A type of cytokine, chemokines play an important role in the body’s immune system response. Chemokines help the body fight infections, inflammatory conditions, and other diseases by attracting certain types of white blood cells to areas of inflammation.
Cytokine storm: also called hypercytokinemia, cytokine release syndrome (CRS), or cytokine associated toxicity. A severe immune system reaction that causes excessive and uncontrolled release of pro-inflammatory cytokines, causing widespread tissue and organ damage. Can be life threatening.
Cytokine: A signaling protein made by certain immune and non-immune cells that affects the immune system. Some cytokines stimulate the immune system and others slow it down. Examples of cytokines are interleukins, interferons, and colony-stimulating factors.
Endothelial damage /dysfunction: When endothelial cells are damaged by a virus or medical condition, the endothelium cannot perform its regular duties. This can cause your body’s immune response to kick in and trigger inflammation where the damage is.
Endothelium: A single layer of cells that line all the blood vessels and lymphatic vessels in your body. Considered an endocrine organ, it contracts and relaxes blood vessels, manages the amount of fluid that passes from blood into your tissues, and prevents thrombosis. It covers 3,000 to 6,000 square meters of a typical person’s body.
Epstein-Barr Virus (EBV): A member of the herpes virus family, one of the most common human viruses in the world. Can cause infectious mononucleosis and other illnesses, and spreads through bodily fluids. Associated with many serious diseases.
Gut permeability/Intestinal permeability: a term describing the control of material passing from inside the GI tract through the gut wall into the rest of the body. Some permeability is normal, allowing nutrients to pass through to the body. Barrier function is important for keeping antigens and other potentially harmful substances in the intestine. Evidence suggests abnormally increased intestinal permeability may play a role in some chronic diseases and inflammatory conditions. The most well understood condition with observed increased intestinal permeability is celiac disease, Crohn’s disease, and Irritable Bowel Syndrome.
Immune Privileged Sites: These are specific areas of the body — such as the eyes, brain, spinal cord, testes, and placenta — where immune responses are limited or actively suppressed to protect delicate tissues from potential damage caused by inflammation. This immune tolerance helps prevent collateral damage in sensitive regions but can also allow pathogens or antigens to persist undetected. Research suggests that in Long COVID, persistent SARS-CoV-2 viral material has been found in these immune-privileged sites, potentially contributing to ongoing symptoms.
Interferons (IFN): A type of cytokine (signaling protein) and type of immunomodulating agent – it helps the body’s immune system fight infection and other diseases. Interferons are made in the body by white blood cells and other cells. There are three main types of interferons: interferon-alfa, interferon-beta, and interferon-gamma. Named after its ability to “interfere” with viral replication, IFNs signal to other cells to activate their defenses against pathogens.
Leaky Gut Syndrome: A condition that is not yet fully understood, where increased gut permeability causes chronic illness symptoms. An overly leaky gut may trigger inflammation and gut flora changes that could affect the digestive tract and other areas of the body. Studies show that a leaky gut may be associated with other autoimmune diseases such as multiple sclerosis, lupus, and type 1 diabetes, as well as chronic illnesses like ME/CFS, fibromyalgia, arthritis, and many more ailments. Clinical studies in humans are needed to show causation.
Microclots: Tiny blood clots that appear as small particles in the blood, which may obstruct blood flow in capillaries resulting in a lack of oxygenation of vital tissues that cause symptoms. Microclots are made of two proteins called amyloid and fibrin, which differs from normal blood clots that contain cells called platelets and fibrin.
Spike Protein: Viruses are contained within something called a “viral envelope”, which is typically made up of three proteins: the membrane protein, the envelope protein, and the spike protein. Spike proteins play a significant role in viral entry, where they easily bind to cell-surface receptors such as the ACE2 in order to infect a cell.
T Cell: Also called T lymphocyte and thymocyte. T cells are a type of white blood cell that develop from stem cells in the bone marrow and mature in the thymus gland. They are a key part of the immune system in that they help protect the body from infection and may help fight cancer.
Medications and treatments
DAO: Stands for Diamine Oxidase, and is an enzyme which is produced in the small intestine and breaks down histamine from food. When DAO is lacking, histamine can build up and trigger symptoms including headaches, fatigue, and gastrointestinal discomfort. This is an issue that many longhaulers experience, which is why they supplement DAO, commonly through beef liver pills.
Electrolytes: Electrolytes are essential minerals – such as sodium, potassium, magnesium, and calcium – that help regulate a wide range of vital functions in the body. They support hydration by maintaining fluid balance, but also play key roles in nerve signal transmission, muscle contraction, blood pressure regulation, and tissue repair. Imbalances in electrolytes can contribute to symptoms like fatigue, brain fog, and weakness, which can be improved by electrolyte intake.
Fludrocortisone: A synthetic steroid medication often used “off-label” to increase salt and water retention in the body in order to treat Postural Orthostatic Tachycardia Syndrome (POTS).
L-Glutamine: Glutamine is a key amino acid that supports both immune and digestive health. It serves as a vital energy source for white blood cells, helping fight infections and repair tissue. In the gut, glutamine strengthens the intestinal barrier, preventing damage and promoting nutrient absorption. Glutamine and L-Glutamine are often used interchangeably. Amino acids can exist in 2 isomeric forms: L-form and D-form, and the L-form is more biologically active in the human body.
LDN: Stands for low dose naltrexone. A dose of naltrexone that is up to 10% of the typical dose given for opioid addiction. Appears to have anti-inflammatory, immune-modulating and pain relief effects. Used “off-label” for these benefits.
Midodrine: A vasoconstrictor used to treat low blood pressure and dizziness caused from sitting to standing. Often prescribed for autonomic nervous system dysfunction.
Occupational Therapy: A type of rehabilitation therapy that helps a patient with a chronic condition like Long Covid accomplish everyday life activities (occupations) using evidence based strategies and interventions.
Pacing: A strategy for managing one’s activity in order to avoid post-exertional malaise (PEM). Involves resting before you are tired, and only increasing activity levels very carefully to avoid relapses.
Tools for Covid precautions
CPC Mouthwash: Cetylpyridinium Chloride (CPC) mouthwash can reduce the viral load in saliva by breaking down the viral membrane.
HEPA filter: Stands for “high efficiency particulate air [filter]". A type of pleated mechanical air filter that can remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). SARS-CoV-2 virus particles hitch a ride with water droplets and aerosols about 1 micron in size, which is why HEPA and Respirators are able to filter out the virus.
Respirator: an item (can be a device or a facemask) worn by a person in order to protect them from breathing in contaminants such as particulate matter (viruses). Different from surgical and cloth masks in its filtering capacity. Common respirator types include: N95, FFP2, KN95, P2, KF94, and DS2.