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The term is usually used to describe bacteria. [1] [2] It describes a property of a bacterium – its inability to cause disease. Most bacteria are nonpathogenic. It can describe the presence of non-disease causing bacteria that normally reside on the surface of vertebrates and invertebrates as commensals.
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 or histoplasmosis.
Their growth and reproduction within their hosts can cause disease. "Germ" refers to not just a bacterium but to any type of microorganism, such as protists or fungi, or other pathogens that can cause disease, such as viruses, prions, or viroids. [1] Diseases caused by pathogens are called infectious diseases. Even when a pathogen is the ...
In some infectious diseases, the severity of symptoms has been shown to be dependent on specific genetic traits of the host. [6] [7] 4. Organisms that look alike but behave differently: In some cases a harmless organism exists which looks identical to a disease causing organism with a microscope, which complicates the discovery process. [8] 5.
[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 exceptions to Koch's postulates include evidence that some pathogens can cause several diseases, such as the varicella-zoster virus causing chickenpox and shingles. Conversely, diseases like meningitis can be caused by a variety of bacterial, viral, fungal, and parasitic pathogens. [11]
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.
Non-pathogenic organisms can become pathogenic given specific conditions, and even the most virulent organism requires certain circumstances to cause a compromising infection. Some colonizing bacteria, such as Corynebacteria sp. and Viridans streptococci , prevent the adhesion and colonization of pathogenic bacteria and thus have a symbiotic ...