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Subviral agents are pathogenic entities that can cause disease, but lack various fundamental properties of viruses. Subviral agents consist of satellites , viroids , prions , defective interfering particles , viriforms , and, most recently, obelisks .
Depending on whether a lax or strict definition is used, the term virusoid may also include Hepatitis D virus (HDV). Like plant virusoids, HDV is circular, single-stranded, and supported by a helper virus (Hepatitis B virus) to form virions; however, the virions possess a much larger genome size (~1700 nt) and encode a protein.
Viroids were shown to consist of short stretches (a few hundred nucleotides) of single-stranded RNA and, unlike viruses, did not have a protein coat. Viroids are extremely small, from 246 to 467 nucleotides, smaller than other infectious plant pathogens; they thus consist of fewer than 10,000 atoms.
A prion / ˈ p r iː ɒ n / ⓘ is a misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death.Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), which are fatal and transmissible neurodegenerative diseases affecting both humans and animals.
Tobacco mosaic virus was the first virus to be identified, as an infectious agent that could pass through porcelain filters, as well as the first to be crystallised. It was among the earliest virus structures to be modelled successfully. Credit: Thomas Splettstoesser (20 July 2012) Portal:Viruses/Selected picture/3
Virus classification showing major ranks This is a list of genera of biological viruses. See also Comparison of computer viruses. This is an alphabetical list of genera of biological viruses. It includes all genera and subgenera of viruses listed by the International Committee on Taxonomy of Viruses (ICTV) 2022 release. [1]
The subsequent demonstration that human prion diseases were transmissible reinforced the importance of spongiform change as a diagnostic feature, reflected in the use of the term "spongiform encephalopathy" for this group of disorders. Prions appear to be most infectious when in direct contact with affected tissues.
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 ...