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Some viruses can cause lifelong or chronic infections where the viruses continue to reproduce in the body despite the host's defence mechanisms. [52] This is common in hepatitis B virus and hepatitis C virus infections. People chronically infected with a virus are known as carriers. They serve as important reservoirs of the virus. [53] [54]
However, Beijerinck only used the phrase "contagium vivum fluidum" in the title of his paper, using the word "virus" throughout. Other scientists began to identify other diseases caused by infectious agents which could pass through a porcelain filter. These became known as "filterable viruses", and later just "viruses".
Influenza A virus and influenza B virus circulate in humans and cause seasonal epidemics, and influenza C virus causes a mild infection, primarily in children. Influenza D virus can infect humans but is not known to cause illness. In humans, influenza viruses are primarily transmitted through respiratory droplets from coughing and sneezing.
Not all virus infections produce a protective immune response in this way. HIV evades the immune system by constantly changing the amino acid sequence of the proteins on the surface of the virion. This is known as "escape mutation" as the viral epitopes escape recognition by the host immune response.
Gamma phage, an example of virus particles (visualised by electron microscopy) Virology is the scientific study of biological viruses.It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they ...
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 are the common cold , gastroenteritis and pneumonia .
The most important aspect of a virus is not whether it’s technically new or simply a variant. It’s the danger that virus poses. Body work: When does a virus grow so much that it gets a new name?
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.