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Virus factors encoded in the genome often control the tropism, routes of virus entry, shedding and transmission. In polioviruses, the attenuating point mutations are thought to induce a replication and translation defect to reduce the virus' ability of cross-linking to host cells and replicate within the nervous system.
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.
An infectious disease agent can be transmitted in two ways: as horizontal disease agent transmission from one individual to another in the same generation (peers in the same age group) [3] by either direct contact (licking, touching, biting), or indirect contact through air – cough or sneeze (vectors or fomites that allow the transmission of the agent causing the disease without physical ...
Plants have elaborate and effective defence mechanisms against viruses. One of the most effective is the presence of so-called resistance (R) genes. Each R gene confers resistance to a particular virus by triggering localised areas of cell death around the infected cell, which can often be seen with the unaided eye as large spots.
Cross-species transmission is the most significant cause of disease emergence in humans and other species. [citation needed] Wildlife zoonotic diseases of microbial origin are also the most common group of human emerging diseases, and CST between wildlife and livestock has appreciable economic impacts in agriculture by reducing livestock productivity and imposing export restrictions. [2]
The process of phagocytosis is accompanied by virus degradation, but if the virus is not neutralized (either due to low affinity binding or targeting to a non-neutralizing epitope), antibody binding may result in virus escape and, therefore, more severe infection. Thus, phagocytosis can cause viral replication and the subsequent death of immune ...
The virulence of the virus may be changed, [5] or a virus could evolve to become adapted to a different host environment than that in which it is typically found. [5] Relatively few passages are necessary to produce a noticeable change in a virus; for instance, a virus can typically adapt to a new host within ten or so passages.
Uncoating is defined by the removal of the virion's protein "coat" and the release of its genetic material. This step occurs in the same area that viral transcription occurs. Different viruses have various mechanisms for uncoating. Some RNA viruses such as Rhinoviruses use the low pH in a host cell's endosomes to activate their uncoating ...