- Abscess
- A localized lesion of infection within a tissue, characterized by the production of pus, and usually caused by more than one microbe.
- Acanthamoeba keratitis
- A serious eye infection causing pain and inflammation around the cornea. This is generally the result of not using proper solutions when cleaning eye contacts, but using tap water instead.
- Acetylcholine
- A chemical messenger that functions to make a nerve-muscle juction. When this messenger is inhibited, the brain cannot signal the muscle to contract. This lack of muscle response is known as ‘flaccid paralysis.’
- Acid fast
- A property by which some stained bacterial cells fail to decolorize when washed with an acid alcohol solution.
- Acidophiles
- Cells that grow well in an acidic atmosphere and stain well with acid dyes; also an alpha cell of the anterior lobe of the pituitary gland or the pancreatic islets.
- Acquired immunity
- Immunity achieved by some other way than by heredity. Artificially acquired immunity is obtained by an injection of vaccine or antiserum.
- Active immunity
- The state achieved by self-production of antibodies (contrast passive immunity).
- Actomomyces
- Filamentous, irregular, nonsporing, Gram-positive rods formerly thought to be fungi.
- Acute
- The current, rapid, short manifestation of disease symptoms.
- Adenoviruses
- Members of a large group of enteroviruses, first identified in the early 1950s, that include the following: rotavirus, calicivirus, and coronavirus families. Adenoviruses are noted for causing diseases of the upper respiratory tract, conjunctiva and some diarrheal diseases in infants. Fifth’s Disease is a common adenovirus infection in children.
- Adherence
- The property of a bacterium that allows it to stick to the surface of a host.
- Adjuvant
- A compound added to an antigen to increase the antibody response.
- Adsorption
- The attachment of a virus to a host cell in the replication process.
- Aerobe
- An organism that requires oxygen for its growth. It may be facultative or obligate (contrast anaerobe). Aerobic Gram-positive bacilli of medical interest to humans include four species: Corynebacterium, Listeria, Erysipelothrix, and Bacillus. The only thing they have in common is that they are all Gram-positive. (contrast anaerobe)
- Aeromonas
- The genus name for a Gram-negative bacilli implicated in cases of diarrhea often caused by contaminated drinking water. The Aeromonas species has been isolated from about 25% of normal individuals, but its frequency of occurrence in those with diarrhea is much greater. The condition of the stools can be watery for up to two weeks, with more severe forms causing bloody dysentery.
- Aerosol
- A suspension of droplets in air so fine that it settles extremely slowly.
- Aflatoxin
- A fungal condition of some plants first described in 1960 when it caused an epidemic of acute enteritis and hepatitis in turkeys. The cause was traced to a peanut extract added to their feed. The fungus responsible is Aspergillus flavus, causing the illness called mycotoxicosis. The same substance affects humans who eat moldy food. Other species of the Aspergillus genus may also produce aflatoxins, as does certain fungi of the genus Penicillium. Aflatoxins are a powerful carcinogens associated with liver cancer. In addition to aflatoxins, several mycotoxins also produce a secondary metabolite of fungi whose effects include nerve damage and the stunting of growth.
- Agglutination
- The reaction between antibody and particle-bound antigens, resulting in the clumping of the particles.
- AIDS (acquired immune deficiency syndrome)
- A disease of the body’s infection-fighting system thought to be caused by the HIV or, specifically, the HTLV-3 virus.
- Algae
- A large group of eucaryotic micro- and macro-scopic organisms that contain chlorophyll, allowing them to carry out photosynthesis. Many are single celled and may be shaped as rods, spheres, or spindler. Others occur as multicellular colonies often visible to the naked eye. Along with scientific names, algae are often referred to as colors – yellow-green, green, red, or brown. One major group, the blue-greens, were discovered to be true procaryotes and are now classified with the cyanobacteria. Thousands of different species of algae exist and are found in most moist environments. The only human health problem commonly associated with algae is from their ability to produce toxins, which are then consumed by aquatic animals. Toxin levels are highest during the summer months and are often retained in shellfish.
- Alkaloid
- A nitrogenous organic chemical derived from plants or fungi that may have medicinal properties when taken in small quantities. In large doses, alkaloids are usually poisonous. Examples include atropine, muscarine, quinine, and strychnine.
- Alkalophiles
- Cells that grow best in an alkaline environment.
- Allergen
- An ordinarily innocuous foreign substance that can elicit an adverse immunological response in a sensitized person.
- Allergy
- A harmful immune reaction; an immediate or delayed type hypersensitivity, usually caused by a foreign antigen in food, pollen, or chemicals; of an immediate type or delayed-type hypersensitivity.
- Alpha hemolysis
- The incomplete rupture of red blood cells by bacterial enzymes (contrast beta hemolysis).
- Amebiasis
- An infection of one-celled parasitic protozoa called amebas. It is spread by contaminated food and drink and affects the colon and liver.
- Amino acid
- Any one of twenty-five known organic acids containing an amino group that link together into polypeptide chains to form proteins.
- Amoeba (also spelled ameba)
- Any member of the protozoans of the genus Amoeba that has an indefinite changeable form.
- Amoebicidal
- A substance used to destroy amoebae.
- Amoeboid movement
- A type of mobility used by certain protozoa.
- Amphoteric
- Having the ability to act either as an acid or a base.
- Amylase
- An enzyme that breaks down starch into disaccharides.
- Anabolism
- The constructive metabolism in which energy is used to synthesize large molecules from simpler components. (contrast catabolism).
- Anaerobe
- An organism that does not require oxygen for growth, with some being killed outright when coming in contact with oxygen (contrast aerobe). Anaerobic bacteria of medical interest are usually separated into two groups of those with and those without spores. The spore-forming ones are all members of the genus Clostridium, that produce powerful exotoxins that cause such diseases as tetanus, botulism, wound botulism, cellulitis, gas gangrene, and food poisonings. The nonspore-forming group include both Gram-positive and Gram-negative cocci, bacilli, and spirochetes and form a significant portion of the body’s normal flora. Nonspore-forming anaerobes that cause disease in humans include the following: Bacteroides (responsible for peritonitis, brain and liver abscesses, gynecologic/pulmonary/upper respiratory diseases, wound infections, and bacteremia); Fusobacterium (responsible for liver abscesses, gynecologic/pulmonary/upper respiratory diseases, wound infections, and bacteremia); Propionibacterium (responsible for upper respiratory infections); Eubacterium (responsible for some tissue infections); and, Villonella (responsible for some tissue infections).
- Anaphylatoxins
- The C3a and C5a fractions of complement which act to mimic some of the reactions of anaphylaxis.
- Anaphylaxis (anaphylactic shock)
- The violent allergic reaction caused by an antigen-antibody reaction. It is life-threatening in a very short period of time. Symptoms include fainting, palpitations, loss of color, difficulty breathing, and shock.
- Androgen
- A male sex hormone.
- Anemia
- A reduction of the hemoglobin in the blood, causing fatigue, breathlessness, and pallor. Aplastic anemia is a disease that results when the blood-forming cells in the bone marrow fail to grow and divide, causing a deficiency of blood cells (white, red, and platelets) that differs from Pernicious anemia, which is a disorder marked by inadequate production of red blood cells resulting from a nutritional deficit as a lack of iron, folic acid, or vitamin B12.
- Animal bites
- These account for millions of dollars in direct medical care each year in the US alone. Dog bites frequently are infected with pasteurella, staphylococci, and Weeksiella. Therefore, it is not a good practice, as some believe, to have a dog lick a wound. All animals and humans, can inflict bites that can start serious infections as a result of the pathogens found in their mouths as normal flora.
- Anisakine larvae
- A form of parasite common to fish (Pacific salmon, Pacific rockfish or red snapper, herring, and cod). After being consumed in raw, undercooked, pickled, or smoked fish, the larvae penetrate the walls of the intestines, causing severe inflammation and pain. The symptoms mimic appendicitis, gastric ulcer, or stomach cancer, and often require surgery to remove the worm. This type of surgery is common in Japan where raw fish is a dietary staple. Commercial blast-freezing seems to be the most effective means of killing the larvae in fish.
- Anopheles
- A genus of mosquito, known to transmit the malaria parasite to humans. The species is gambiae.
- Anorexia
- The medical term for the loss of appetite that leads to the inability to eat. It is a common condition to most illnesses. Anorexia nervosa is an extreme loss of appetite causing severe weight loss and starvation.
- Anoxygenic photosynthesis
- The use of light energy to synthesize ATP by cyclic photophosphorylation without oxygen production in green and purple bacteria.
- Anthelmintic
- A substance that destroys or expels intestinal worms.
- Anther
- That part of a stamen that produces and releases pollen causing allergies in some.
- Anthocyanidin
- A particular class of flavonoids which gives plants, fruits, and flowers color ranging from red to blue.
- Anthraquinones
- Glycoside compounds that produce dyes and purgatives.
- Anthrax
- An infectious disease caused by spores of certain bacteria (Bacillus anthracis) that can produce three variations of the disease: Cutaneous anthrax (skin contact); Pulmonary anthrax (inhalation); and Intestinal anthrax (eating spores).
- Antibacterial
- A compound or a process detrimental to the growth or survival of bacteria.
- Antibiotic
- A chemical agent produced by one organism that is harmful to other organisms; a substance produced by one tiny organism, usually a bacterium or fungus, that can be extracted and purified to be used medicinally in the treatment of infections.
- Antibodies
- Proteins manufactured by lymphocytes present in serum or other body fluids that combine specifically with antigen to respond to foreign materials entering the bodies of higher organisms. They react to foreign matter by coagulating it, making it easier for the body to dispose of and are a principle component of immunity. A blocking antibody is one whose production is induced by cancer cells of tissue transplants and blocks the destruction of those cells by cytotoxic T cells.
- Antibiotics
- Drugs that inhibit or destroy microorganisms, but ineffective against viruses.
- Antigen
- Any substance introduced into the body that can stimulate antibody production against it. Antigens may vary in size, but are usually large molecules that have a unique structure so that antibodies formed against an antigen will recognize and bind specifically to that particular antigen. Proteins and polysaccharides are usually antigenic.
- Antigen-presenting cell (APC)
- Cells that process and present antigen to T lymphocytes.
- Antigenic determinants
- That portion of an antigen that interacts with an immunoglobulin or T cell receptor.
- Antigenic drift
- Minor changes in the influenza virus due to gene mutation. Yearly flu epidemics are known as ‘antigenic drift.’
- Antigenic shift
- Minor changes in the influenza virus caused by gene reassortment. Such viruses may “drift” globally, but do not “shift” their genetic makeup to another species.
- Antimicrobial
- A compound that is capable of killing or stopping the growth of a microbe. Antibiotics are microbials.
- Antiseptic
- A germacidal agent that kills or inhibits microbial growth, but is not harmful to human tissue. An antiseptic can be used on human skin or tissue, but not for an inanimate object. These compounds include alcohol (ethanol or isopropanol), iodine (iodophor), povidone-iodine (Betadine), hydrogen-peroxide, chlorhexidine (Hibiclens), and hexachlorophene (Phisohex).
- Antiserum
- Serum that contains antibodies.
- Antitoxin
- An antibody that specifically interacts with and neutralizes a toxin or toxoid.
- Apharesis
- A procedure in which a patient’s blood is passed through a machine to exchange a specific component, as plasma.
- Apoptosis
- The self-destruction, or suicide, of a cell. It is of widespread occurrence, as in the development of lymphocytes in the thymus, the disappearance of the tadpole’s tail, or the shrinking of the human embryo’s tail to a curled vestige behind the anus commonly known as “the tail bone.”
- Apraxia
- The inability to perform normally easy actions. Examples include the misuse of everyday objects because of misidentification and the inability to perform complex motions with the limbs.
- Arbovirus (arthropod borne)
- A virus transmitted by insect vectors and frequently associated with encephalitis, yellow fever, denge fever, and innumerable tropical and hemorrhagic fevers. There are more than 520 known arboviruses of which about 100 cause disease in humans.
- Archaea
- An evolutionarily distinct group or domain of prokaryotes consisting of the methanogens, most extreme halophiles and hyperthermophiles, and Thermoplasma. Archaebacteria is the old term for the Archaea which are found only in organic soil and not in chemically treated agricultural land. These bacteria are necessary to mediate the flow of minerals, especially nitrogen, and nutrients needed to fend off pathogens. Working with other microbes, they create an unseen ecosystem that is the foundation of agriculture.
- ARC
- An AIDS-related complex in which different forms of the AIDS virus are present, but the individual remains clinically healthy.
- ARDS (acute respiratory distress syndrome)
- A disorder of the lung tissue caused by bacterial toxins, producing infection, shock, burns, or other insults in which the capillaries become leaky and the air spaces fill with fluid. This prevents the absorption of oxygen into the lungs. When patients die of pneumococcal pneumonia, they usually die of ARDS.
- Arenaviruses
- A group of about twelve viruses generally restricted to Africa and South America, with each infecting a special species of rodent. In the rodent, the infection is harmless, but when spread to humans, it causes such severe diseases as Lassa fever, South American haemorrhagic fevers, and LCM (lymphocytic choriomeningitis).
- Arthralgia
- Severe joint pain.
- Arthritis
- A painful condition of the joints caused by any number of pathogens which can be the direct consequence of infections or as a result of an immunological reaction. Septic arthritis (monoarthritis – typically affects only one joint) results from joints becoming infected by bacteria. Prosthetic joints often fail because of chronic infections caused by Staph introduced during surgery. The most common cause of septic arthritis in otherwise healthy joints is Staph aureus. Salmonella and Haemophilus influenzae may cause septic arthritis in children. In gonococcal arthritis, several joints may be simultaneously affected (polyarthritis). Occasionally, mycobacterium tuberculosis can cause arthritis which typically affects the hip or knee joints. A number of viruses can cause reactive arthritis as a result of circulating immune complexes. Notable causes of reactive polyarthritis are HBV and rubella virus. Polyarthritis is often caused by rubella virus following vaccinations with live attenuated vaccine strains. Adult men can also suffer from a reactive polyarthritis following mumps. Rheumatic fever, a rare complication of a S.pyogenes infection, can also produce inflammed joints. There is also evidence of ankylosing spondylitis, a severe degenerative disease affecting the bones of the spine. This condition is usually seen in people with HLA-B27 tissue type, and is thought to be caused by cross-reacting antibodies somewhat similar to rheumatic fever. Another reactive arthritis is Reiter’s syndrome, an uncommon complication of chlamydial infection. It is characterized by conjunctivitis and arthritis, affecting mostly the lower back and legs, as well as producing urethritis. It, too, mostly affects young men with HLA-B27 tissue type, and is thought to be mediated through an immune mechanism. The syndrome is also associated with certain GI infections caused by Shigella, Yersinia, and Campylobacter.
- Arthropods
- A large group of invertebrate animals from the phylum Arthropoda that include bilaterally symmetrical animals with hard, segmented bodies having jointed legs. They are the largest known group, and include arachnids, crustaceans, and insects. They are commonly associated with infectious diseases acting as vectors for bacteria, parasites, etc.
- Ascaris lumbricoides
- An intestinal roundworm which may grow to be over eight inches long.
- Aseptic (also spelled aeseptic)
- Free of microorganisms.
- Aspergillus
- A genus of mold that can cause lung and brain infections (aspergillosis) in patients with weakened immune systems. Old TB sites are a favorite spot for fungal development.
- Asphyxiation
- The lack of oxygen that contributes to unconsciousness or death, common in such diseases as diphtheria, end stage tetanus, etc.
- Aymptomatic
- No symptoms are apparent.
- Athrospore
- A fungal spore formed as the cell walls increase in thickness. Each of the cells in hyphae may become an arthrospore, which are very resistant to drying.
- ATP (Adenosine triphosphate)
- The principal energy carrier of a cell.
- Attachment pili
- A type of pili that help bacteria adhere to surfaces.
- Attachment site
- The position at which an organism attaches itself to a host tissue.
- Attending
- A senior physician who supervises physicians in training.
- Attenuated
- The condition of an organism from which virulence factors have been removed.
- Attenuated vaccine
- A type of vaccine made from living microorganisms that have been selected for their lack of virulence.
- Attenuation
- The process whereby microbes are treated so that they can no longer cause overt disease, yet they remain able to cause infection; the selection of nonvirulent strains of a pathogen still capable of immunizing; also a process that plays a role in the regulation of enzymes involved in amino acid biosynthesis.
- Atom
- The smallest particle of an element, having all its properties consisting of units made up of protons, electrons, and neutrons.
- Autoantibody
- Antibodies that react to self-antigens.
- Autoimmune Diseases
- Result when the body’s own immune system no longer recognizes “self” from foreign invaders and continues to attack. It is not yet known exactly what causes the body to fail to recognize proteins as its own and to react to them as if they were foreign matter. This can happen in various parts of the body, creating a number of diseases. For instance, these can include: Juvenile diabetes (pancreas); Myasthenia gravis (skeletal muscles); Goodpasture’s syndrome (kidney); Rheumatoid arthritis (cartilage); Hashimoto’s disease – hypothyroidism (thyroid); some cases of male infertility (sperm cells); pernicious anemia (intrinsic factor); systemic lupus erythematosis (DNA, cardiolipin, nucleoprotein, blood clotting factors); Addison’s disease (adrenal glands); Allergic encephalomyelitis and multiple sclerosis (brain).
- Autoimmunity
- An immune response directed against the body’s own tissues, causing disease.
- Autoinfection
- An infection caused by microorganisms that persist on or in the body.
- Autotroph
- An organism capable of synthesizing necessary nutrients if water, carbon dioxide, inorganic salts, and a source of energy are available.
- Auxotroph
- A mutant that has a growth factor requirement (contrast prototroph).
- Avirulent
- Not virulent, referring to microorganisms that are not capable of producing an infectious process.
- AZT (zidovudine)
- The well-known antiviral drug called triazidothymidine, used to inhibit an enzyme called “reverse transcriptase,” a method the HIV (virus) uses to copy its own genes into the genes of the cells it infects in humans. Since viruses can mutate and change their structure so that drugs are no longer effective, AZT and other reverse-transcriptase inhibitors, are bound to lose their effectiveness.
