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Within the host, pathogens can do a variety of things to cause disease and trigger the immune response. Microbes and fungi cause symptoms due to their high rate of reproduction and tissue invasion. This causes an immune response, resulting in common symptoms as phagocytes break down the bacteria within the host.
For infections to occur, the virus has to hijack host factors and evade the host immune response for efficient replication. Viral replication frequently requires complex interactions between the virus and host factors that may result in deleterious effects in the host, which confers the virus its pathogenicity.
Infections can be caused by a wide range of pathogens, most prominently bacteria and viruses. [2] Hosts can fight infections using their immune systems. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response. Treatment for infections depends on the type of pathogen involved.
An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellular bacteria, protozoa, helminths, and fungi which could cause serious problems to the health of the host organism if not cleared from the body.
Here, the immune system adapts its response during an infection to improve its recognition of the pathogen. This improved response is then retained after the pathogen has been eliminated, in the form of an immunological memory, and allows the adaptive immune system to mount faster and stronger attacks each time this pathogen is encountered. [4] [5]
When host cells die, either by apoptosis or by cell injury due to an infection, phagocytic cells are responsible for their removal from the affected site. [9] By helping to remove dead cells preceding growth and development of new healthy cells, phagocytosis is an important part of the healing process following tissue injury.
In biology, it refers to damage caused to an organism by its own immune response, as a result of an infection. It could be due to mismatch between pathogen and host species, and often occurs when an animal pathogen infects a human (e.g. avian flu leads to a cytokine storm which contributes to the increased mortality rate).
Inflammation is one of the first immune responses to pathogenic infection that many host organisms possess. Inflammation involves an elevated temperature surrounding the site of infection, accumulation of CO 2 and organic acids, and a decrease in the infected tissue's oxygen tension in response to pathogen-induced cell damage.