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A contagious disease is an infectious disease that can be spread rapidly in several ways, including direct contact, indirect contact, and Droplet contact. [1] [2] These diseases are caused by organisms such as parasites, bacteria, fungi, and viruses. While many types of organisms live on the human body and are usually harmless, these organisms ...
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.
An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection. Infections can be caused by a wide range of pathogens, most prominently bacteria and viruses. [2] Hosts can fight infections using their immune systems.
Life-cycle of a typical virus (left to right); following infection of a cell by a single virus, hundreds of offspring are released. When a virus infects a cell, the virus forces it to make thousands more viruses. It does this by making the cell copy the virus's DNA or RNA, making viral proteins, which all assemble to form new virus particles. [37]
A zoonosis (/ z oʊ ˈ ɒ n ə s ɪ s, ˌ z oʊ ə ˈ n oʊ s ɪ s / ⓘ; [1] plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite, or prion) that can jump from a non-human vertebrate to a human.
A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions) attach to and enter susceptible cells. [ 1 ] Examples include the common cold , gastroenteritis , COVID-19 , the flu , and rabies .
Examples of vertical transmission include hepatitis B virus and HIV, where the baby is born already infected with the virus. [116] Another, more rare, example is the varicella zoster virus , which, although causing relatively mild infections in children and adults, can be fatal to the foetus and newborn baby.
[2] [3] Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus. [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]