infection, invasion of plant or animal tissues by microorganisms, i.e., bacteria bacteria [pl. of bacterium], microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera .
..... Click the link for more information. , viruses virus, parasite with a noncellular structure composed mainly of nucleic acid within a protein coat. Viruses usually are too small (100–2,000 Angstrom units) to be seen with the light microscope and thus must be studied by electron microscopes.
..... Click the link for more information. , viroids viroid, microscopic infectious agent, much smaller than a virus , that infects higher plants such as potatoes, tomatoes, chrysanthemums, and cucumbers, causing stunted or distorted growth and sometimes death. It can be transmitted by pollen, seed, or farm implements.
..... Click the link for more information. , fungi Fungi (fŭn`jī), kingdom of heterotrophic single-celled, multinucleated, or multicellular organisms, including yeasts, molds, and
..... Click the link for more information. , rickettsias rickettsia (rĭkĕt`sēə)
..... Click the link for more information. , and protozoans protozoan (prō'təzō`ən), informal term for the unicellular heterotrophs of the kingdom Protista .
..... Click the link for more information. . The invasion of body tissues by parasitic worms worm, common name for various unrelated invertebrate animals with soft, often long and slender bodies. Members of the phylum Platyhelminthes , or the flatworms, are the most primitive; they are generally small and flat-bodied and include the free-living planarians
..... Click the link for more information. and other higher organisms is commonly referred to as infestation.

Invading organisms such as bacteria produce toxins toxin, poison produced by living organisms. Toxins are classified as either exotoxins or endotoxins. Exotoxins are a diverse group of soluble proteins released into the surrounding tissue by living bacterial cells.
..... Click the link for more information. that damage host tissues and interfere with normal metabolism; some toxins are actually enzymes that, by breaking down host tissues, prevent the localization of infections. Other bacterial substances destroy the host's phagocytes. Viruses and retroviruses retrovirus, type of RNA virus that, unlike other RNA viruses, reproduces by transcribing itself into DNA. An enzyme called reverse transcriptase allows a retrovirus's RNA to act as the template for this RNA-to-DNA transcription.
..... Click the link for more information. are parasitic on host cells, causing cellular degeneration, as in rabies rabies (rā`bēz, ră`–) or hydrophobia
..... Click the link for more information. , poliomyelitis poliomyelitis (pō'lēōmī'əlī`tĭs), polio, or infantile paralysis,
..... Click the link for more information. , and AIDS AIDS or acquired immunodeficiency syndrome, fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders.
..... Click the link for more information. , or cellular proliferation, as in warts wart, circumscribed outgrowth of the skin caused by a filterable virus that is readily transmitted. Warts may appear anywhere on the skin but are most common on the hands.
..... Click the link for more information. and cold sores. Some viruses have been associated with the development of certain cancers cancer, in medicine, common term for neoplasms, or tumors, that are malignant. Like benign tumors, malignant tumors do not respond to body mechanisms that limit cell growth.
..... Click the link for more information. . Substances produced by many invading organisms cause allergic sensitivity in the host; the immune response to virus infection has been implicated in some diseases (see allergy allergy, hypersensitive reaction of the body tissues of certain individuals to certain substances that, in similar amounts and circumstances, are innocuous to other persons. Allergens, or allergy-causing substances, can be airborne substances (e.g.
..... Click the link for more information. ).

Infections may be spread via respiratory droplets, direct contact, contaminated food, or vectors, such as insects. They can also be transmitted sexually (see sexually transmitted diseases sexually transmitted disease (STD) or venereal disease, term for infections acquired mainly through sexual contact. Five diseases were traditionally known as venereal diseases: gonorrhea , syphilis , and the less common granuloma inguinale,
..... Click the link for more information. ) and from mother to fetus. Immunity immunity, ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity.
..... Click the link for more information. is the term used to describe the capacity of the host to respond to infection. Drugs that help fight infections include antibiotics antibiotic, any of a variety of substances, usually obtained from microorganisms, that inhibit the growth of or destroy certain other microorganisms.

Types of Antibiotics

..... Click the link for more information. and antiviral drugs antiviral drug, any of several drugs used to treat viral infections. The drugs act by interfering with a virus's ability to enter a host cell and replicate itself with the host cell's DNA.
..... Click the link for more information. .

See also specific diseases, diseases of plants diseases of plants. Most plant diseases are caused by fungi, bacteria, and viruses. Although the term disease is usually used only for the destruction of live plants, the action of dry rot and the rotting of harvested crops in storage or transport is similar
..... Click the link for more information. .

Bibliography

See J. Waller, The Discovery of the Germ (2003).

infection

Invasion of the body by various agents—including bacteria, fungi (see fungus), protozoans, viruses, and worms—and its reaction to them or their toxins. Infections are called subclinical until they perceptibly affect health, when they become infectious diseases. Infection can be local (e.g., an abscess), confined to one body system (e.g., pneumonia in the lungs), or generalized (e.g., septicemia). Infectious agents can enter the body by inhalation, ingestion, sexual transmission, passage to a fetus during pregnancy or birth, wound contamination, or animal or insect bites. The body responds with an attack on the invader by leukocytes, production of antibodies or antitoxins, and often a rise in temperature. The antibodies may result in short-term or lifelong immunity. Despite significant progress in preventing and treating infectious diseases, they remain a major cause of illness and death, particularly in regions of poor sanitation, poor nutrition, and crowding.

Infection

A term considered by some to mean the entrance, growth, and multiplication of a microorganism (pathogen) in the body of a host, resulting in the establishment of a disease process. Others define infection as the presence of a microorganism in host tissues whether or not it evolves into detectable pathologic effects. The host may be a bacterium, plant, animal, or human being, and the infecting agent may be viral, rickettsial, bacterial, fungal, or protozoan.

A differentiation is made between infection and infestation. Infestation is the invasion of a host by higher organisms such as parasitic worms. See Epidemiology, Medical bacteriology, Medical mycology, Medical parasitology, Opportunistic infections, Pathogen, Virus

Infection (redirected from transmissible infection)

Types of Antibiotics

Bibliography

infection

Infection
(redirected from transmissible infection)