Paul M. Insel,
Stanford University School of Medicine
Walton T. Roth,
Stanford University School of Medicine
| *infection | Invasion of the body by a microorganism.
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| pathogen | An organism that causes disease.
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| toxin | A poisonous substance produced by a microorganism.
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| *vector | An insect, rodent, or other organism that carries and transmits a pathogen from one host to another.
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| lymphatic system | A system of vessels and organs that picks up excess fluid, proteins, lipids, and other substances from the tissues; filters out pathogens and other waste products; and returns the cleansed fluid to the general circulation.
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| systemic infection | An infection spread by the blood or lymphatic system to large portions of the body.
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| neutrophil | A type of white blood cell that engulfs foreign organisms and infected, damaged, or aged cells; particularly prevalent during the inflammatory response.
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| macrophage | A large phagocytic (cell-eating) cell that devours foreign particles.
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| natural killer cell | A type of white blood cell that directly destroys virus-infected cells and cancer cells.
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| lymphocytes | A white blood cell continuously made in lymphoid tissue as well as in bone marrow.
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| T cell | A lymphocyte that arises in bone marrow and matures in the thymus (thus its name).
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| B cell | A lymphocyte that matures in the bone marrow and produces antibodies.
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| helper T cell | A lymphocyte that helps activate other T cells and may help B cells produce antibodies.
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| killer T cell | A lymphocyte that kills body cells that have been invaded by foreign organisms; also can kill cells that have turned cancerous.
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| suppressor T cell | A lymphocyte that inhibits the growth of other lymphocytes.
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| antibody | A specialized protein, produced by white blood cells, that can recognize and neutralize specific microbes.
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| memory T and B cells | Lymphocytes generated during an initial infection that circulate in the body for years, "remembering" the specific antigens that caused the infection and quickly destroying them if they appear again.
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| autoimmune disease | A disease in which the immune system attacks the person's own body.
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| antigen | A marker on the surface of a foreign substance that immune system cells recognize as nonself and that triggers the immune response.
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| histamine | A chemical responsible for the dilation and increased permeability of blood vessels in allergic reactions.
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| cytokine | A chemical messenger produced by a variety of cell types that helps regulate many cell functions; immune system cells release cytokines that help amplify and coordinate the immune response.
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| immunity | Mechanisms that defend the body against infection; specific defenses against specific pathogens.
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| acquired immunity | The body's ability to mobilize the cellular "memory" of an attack by a pathogen to throw off subsequent attacks; acquired through vaccination as well as the normal immune response.
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| incubation | The period when bacteria or viruses are actively multiplying inside the body's cells; usually a period without symptoms of illness.
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| prodromal period | The stage of an infection, following incubation, during which initial symptoms begin to appear but the host does not feel ill; a highly contagious period.
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| *vaccine | A preparation of killed or weakened microorganisms, inactivated toxins, or components of microorganisms that is administered to stimulate an immune response; a vaccine protects against future infection by the pathogen.
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| allergy | A disorder caused by the body's exaggerated response to foreign chemicals and proteins; also called hypersensitivity.
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| allergen | A substance that triggers an allergic reaction.
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| bacterium (plural, bacteria) | A microscopic single-celled organism; about 100 bacterial species can cause disease in humans.
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| *tuberculosis (TB) | A chronic bacterial infection that usually affects the lungs.
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| *mycoplasma | A small bacterium with an incomplete cell wall that may cause sore throats, ear infections, and pneumonia.
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| *rickettsia | A bacterium that can reproduce only inside living cells, transmitted by ticks, fleas, and lice; causes Rocky Mountain spotted fever and typhus.
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| *virus | A very small infectious agent composed of nucleic acid (DNA or RNA) surrounded by a protein coat; lacks an independent metabolism and reproduces only within a host call.
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| *parasite | An organism that lives on or within a living host; the relationship benefits the parasite and harms the host.
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| contagious disease | A disease that can be transmitted from one person to another; most are viral diseases, such as the common cold and flu.
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| *influenza | Infection of the respiratory tract by the influenza virus, which is highly infective and adaptable; the form changes so easily that every year new strains arise, making treatment difficult; commonly known as the flu.
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| *herpesvirus | A family of viruses responsible for cold sores, mononucleosis, chicken pox, and the STD known as herpes, frequently cause latent infections.
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| pandemic | A disease epidemic that is unusually severe or widespread; often used to refer to worldwide epidemics affecting a large proportion of the population.
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| endemic | Persistent and relatively widespread in a given population.
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| epidemic | The occurrence in a particular community or region of more than the expected number of cases of a particular disease.
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| poliomyelitis | A disease of the nervous system, sometimes crippling; vaccines now prevent most cases of polio.
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| *fungus | A single-celled or multicelled organism that absorbs food from living or dead organic matter; examples include molds, mushrooms, and yeasts. Fungal diseases include yeast infections, athlete's foot, and ringworm.
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| *protozoan | A microscopic single-celledorganismthat often produces recurrent, cyclical attacks of disease.
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| *malaria | A severe, recurrent, mosquito-borne infection caused by the Plasmodium protozoan.
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| parasitic worm | A pathogen that causes intestinal and other infections; includes tapeworms, hookworms, pinworms, and flukes.
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| anaphylaxis | A severe systemic hypersensitive reaction to an allergen characterized by difficulty breathing, low blood pressure, heart arrhythmia, seizure, and sometimes death.
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| pneumonia | Inflammation of the lungs, typically caused by infection or exposure to chemical toxins or irritants.
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| meningitis | Infection of the membranes covering the brain and spinal cord (meninges)
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| streptococcus | Any of a genus (Streptococcus) of spherical bacteria; streptococcal species can cause skin infections, strep throat, rheumatic fever, pneumonia, scarlet fever, and other diseases.
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| staphylococcus | Any of a genus (Staphylococcus) of spherical, clustered bacteria commonly found on the skin or in the nasal passages; staphylococcal species may enter the body and cause such conditions as boils, pneumonia, and toxic shock syndrome.
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| toxic shock syndrome (TSS) | Sudden onset of fever, aches, vomiting, and peeling rash, followed in some cases by shock and inflammation of multiple organs; often caused by a toxin produced by Staphylococcus aureus.
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| encephalitis | Inflammation of the brain; fever, headache, nausea, and lethargy are common initial symptoms, followed in some cases by memory loss, seizures, brain damage, and death.
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| hepatitis | Inflammation of the liver, which can be caused by infection, drugs, or toxins.
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| jaundice | Increased bile pigment levels in the blood, characterized by yellowing of the skin and the whites of the eyes.
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| giardiasis | An intestinal disease caused by the protozoan Giardia lamblia.
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| prion | Proteinaceous infectious particles thought to be responsible for a class of neurodegenerative diseases known as transmissible spongiform encephalopathies; Creutzfeld-Jakob disease in humans and bovine spongiform encephalopathy ("mad cow disease") are examples of prion diseases.
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2002 McGraw-Hill Higher Education