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In biology, a pathogen (Greek: πάθος, pathos "suffering", "passion" and -γενής, -genēs "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. [1] The term pathogen came into use in the 1880s.
Biochemical tests used in the identification of infectious agents include the detection of metabolic or enzymatic products characteristic of a particular infectious agent. Since bacteria ferment carbohydrates in patterns characteristic of their genus and species , the detection of fermentation products is commonly used in bacterial identification.
The following outline is provided as an overview of and topical guide to concepts related to infectious diseases in humans.. Infection – transmission, entry/invasion after evading/overcoming defense, establishment, and replication of disease-causing microscopic organisms (pathogens) inside a host organism, and the reaction of host tissues to them and to the toxins they produce.
An infectious disease agent can be transmitted in two ways: as horizontal disease agent transmission from one individual to another in the same generation (peers in the same age group) [3] by either direct contact (licking, touching, biting), or indirect contact through air – cough or sneeze (vectors or fomites that allow the transmission of the agent causing the disease without physical ...
Epstein–Barr virus infectious mononucleosis (Mono) Diagnostic modalities for infectious mononucleosis include: Person's age, with highest risk at 10 to 30 years. Medical history, such as close contact with other people with infectious mononucleosis; Physical examination, including palpation of any enlarged lymph nodes in the neck, or enlarged ...
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. [1] Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. [2] [3] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.
Most species of bacteria are harmless and are often beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. [2] By contrast, several thousand species are part of the gut flora present in the digestive tract. [citation needed]
Viruses are among the smallest infectious agents, and are too small to be seen by light microscopy; most of them can only be seen by electron microscopy. Their sizes range from 20 to 300 nanometres ; it would take 30,000 to 500,000 of them, side by side, to stretch to one centimetre (0.4 in). [ 23 ]