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A microorganism, or microbe, [a] is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells.. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from sixth century BC India.
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.
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.
Many protozoan pathogens are human parasites, causing serious diseases such as malaria, giardiasis, toxoplasmosis, and sleeping sickness. Some of these protozoa have two-phase life cycles, alternating between proliferative stages (e.g., trophozoites ) and resting cysts , enabling them to survive harsh conditions.
Microorganism produce, change, and utilize nutrient and natural products in numerous ways and this enable them to be ubiquitous. [43] Microbes, especially bacteria, often engage in symbiotic relationships (either positive or negative ) with other microorganisms or larger organisms. [ 44 ]
Microorganisms make up about 70% of the marine biomass. [4] A microorganism, or microbe, is a microscopic organism too small to be recognised adequately with the naked eye. In practice, that includes organisms smaller than about 0.1 mm. [12]: 13
This is a list of pathogens (human or otherwise) in order of size. Classification Binomial name Common name Dimension Size Reference Flatworm animal: Eucestoda ...
A human pathogen is a pathogen (microbe or microorganism such as a virus, bacterium, prion, or fungus) that causes disease in humans. The human physiological defense against common pathogens (such as Pneumocystis ) is mainly the responsibility of the immune system with help by some of the body's normal microbiota .