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Microorganisms are the causative agents in many infectious diseases. The organisms involved include pathogenic bacteria, causing diseases such as plague, tuberculosis and anthrax; protozoan parasites, causing diseases such as malaria, sleeping sickness, dysentery and toxoplasmosis; and also fungi causing diseases such as ringworm, candidiasis ...
Pathogenic bacteria are bacteria that can cause disease. [1] This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and many are beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. [2]
[4] [5] [6] Small animals, such as helminths and insects, can also cause or transmit disease. However, these animals are usually referred to as parasites rather than pathogens. [ 7 ] The scientific study of microscopic organisms, including microscopic pathogenic organisms, is called microbiology , while parasitology refers to the scientific ...
Other organisms invariably cause disease in humans, such as Rickettsia, which are obligate intracellular parasites able to grow and reproduce only within the cells of other organisms. One species of Rickettsia causes typhus , while another causes Rocky Mountain spotted fever .
Their growth and reproduction within their hosts can cause disease. "Germ" refers not just to bacteria but to any type of microorganism, such as protists or fungi, or other pathogens, including parasites, viruses, prions, or viroids. [1] Diseases caused by pathogens are called infectious diseases. Even when a pathogen is the principal cause of ...
Organisms that parasitize fungi are known as mycoparasitic organisms. About 300 species of fungi and fungus-like organisms, belonging to 13 classes and 113 genera, are used as biocontrol agents against plant fungal diseases. [220] Fungi can also act as mycoparasites or antagonists of other fungi, such as Hypomyces chrysospermus, which grows on ...
Infectious disease – illness or disorder when pathogenic (disease-causing) microorganisms, such as bacteria, viruses, fungi, or parasites invade and multiply within the body of a host organism and release toxins, causing various clinical symptoms which can potentially lead to severe health complications or even death. Infectious diseases can ...
Opportunistic infection may be caused by microbes ordinarily in contact with the host, such as pathogenic bacteria or fungi in the gastrointestinal or the upper respiratory tract, and they may also result from (otherwise innocuous) microbes acquired from other hosts (as in Clostridioides difficile colitis) or from the environment as a result of ...