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Virus tropism refers to the virus' preferential site of replication in discrete cell types within an organ. In most cases, tropism is determined by the ability of the viral surface proteins to fuse or bind to surface receptors of specific target cells to establish infection.
Tissue tropism is the range of cells and tissues of a host that support growth of a particular pathogen, such as a virus, bacterium or parasite. [1] [2] Some bacteria and viruses have a broad tissue tropism and can infect many types of cells and tissues. [1] Other viruses may infect primarily a single tissue. [1]
Some viruses can "hide" within a cell, which may mean that they evade the host cell defenses or immune system and may increase the long-term "success" of the virus. This hiding is deemed latency. During this time, the virus does not produce any progeny, it remains inactive until external stimuli—such as light or stress—prompts it to activate.
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. [1] Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. [2] [3] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.
Viruses, however, use a completely different mechanism to cause disease. Upon entry into the host, they can do one of two things. Many times, viral pathogens enter the lytic cycle; this is when the virus inserts its DNA or RNA into the host cell, replicates, and eventually causes the cell to lyse, releasing more viruses into the environment.
The virus often infects many tissues, if not the whole plant, where it can continue to replicate. There are a variety of methods the virus can use to spread throughout the organism but the most common route use the vascular system, otherwise known as the xylem and phloem, and the plasmodesmata, which interconnect adjacent cells.
The human virome is the total collection of viruses in and on the human body. [1] [2] [3] Viruses in the human body may infect both human cells and other microbes such as bacteria (as with bacteriophages). [4] Some viruses cause disease, while others may be asymptomatic.
The virus wraps its delicate nucleic acid with a protein shell known as the capsid, from the Latin capsa, meaning "box," in order to shield it from this hostile environment. Similar to how numerous bricks come together to form a wall, the capsid is made up of one or more distinct protein types that repeatedly repeat to form the whole capsid.