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Humans can be infected with many types of pathogens, including prions, viruses, bacteria, and fungi, causing symptoms like sneezing, coughing, fever, vomiting, and potentially lethal organ failure. While some symptoms are caused by the pathogenic infection, others are caused by the immune system's efforts to kill the pathogen, such as ...
Infections may be caused by bacteria, viruses, fungi, and parasites.The pathogen that causes the disease may be exogenous (acquired from an external source; environmental, animal or other people, e.g. Influenza) or endogenous (from normal flora e.g. Candidiasis).
Microbiology (from Ancient Greek μῑκρος (mīkros) 'small' βίος (bíos) 'life' and -λογία () 'study of') is the scientific study of microorganisms, those being of unicellular (single-celled), multicellular (consisting of complex cells), or acellular (lacking cells).
The English word fungus is directly adopted from the Latin fungus (mushroom), used in the writings of Horace and Pliny. [10] This in turn is derived from the Greek word sphongos (σφόγγος 'sponge'), which refers to the macroscopic structures and morphology of mushrooms and molds; [11] the root is also used in other languages, such as the German Schwamm ('sponge') and Schimmel ('mold').
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.
Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists, some fungi, as well as some micro-animals and plants. Viruses are generally regarded as not living and therefore not considered to be microorganisms, although a subfield of microbiology is virology , the study of viruses.
Viruses are by far the most abundant biological entities on Earth and they outnumber all the others put together. [89] They infect all types of cellular life including animals, plants, bacteria and fungi. [6]: 49 Different types of viruses can infect only a limited range of hosts and many are species-specific.
Like all other organisms, bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from that of eukaryotes and archaea. [ 67 ] Some bacteria produce intracellular nutrient storage granules, such as glycogen , [ 68 ] polyphosphate , [ 69 ] sulfur [ 70 ] or polyhydroxyalkanoates . [ 71 ]