Tolerance to infections

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Tolerance to infection, or disease tolerance, is a mechanism that host organisms can use to fight parasites or pathogens that attack the host. Tolerance is not equivalent to resistance. Disease resistance is the host trait that prevents infection or reduces the number of pathogens and parasites within or on a host.


Tolerance to infection can be illustrated via comparing host performance versus increasing load. This is a reaction norm in which host performance is regressed against increasing disease burden. [1] The slope of the reaction norm defines the degree of tolerance. High tolerance is indicated as a flat slope, i.e., host performance is not influenced by increasing burden. Steep downward slope indicates low tolerance in which host performance is strongly reduced with increasing burden. An upward slope indicates overcompensation in which a host increases its performance with increasing burden. Genetic variation in tolerance and its correlation with resistance, can be quantified using random regression model. [2]

In livestock science, tolerance to infections is sometimes termed disease resilience. [4] [5]

A variety of reactions to pathogens are thought to be involved in tolerance, including superior immune system regulation and supplying pathogens with sufficient nutrients to blunt attacks on cells. [6]

Human tolerance

Humans experience tolerance. For example, 90% of people infected with tuberculosis experience no symptoms. [7] Similarly, many humans tolerate helminth infestations. [6]


Much research makes use of the lethal dose 50 protocol. Subjects are given enough pathogen to kill half of them. The remaining half presumably exhibit the desired tolerance. In many cases, the survivors not only survive but are unaffected by the pathogen.

Research is complicated by the fact that animal protocols typically involve expecting some of the subjects to die, which is not ethical in humans. [6]

Related Research Articles

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An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.

Parasitic disease Medical condition

A parasitic disease, also known as parasitosis, is an infectious disease caused or transmitted by a parasite. Many parasites do not cause diseases as it may eventually lead to death of both organism and host. Parasites infecting human beings are called human parasites. Parasitic diseases can affect practically all living organisms, including plants and mammals. The study of parasitic diseases is called parasitology.

<i>Mycobacterium tuberculosis</i> Species of bacterium that causes tuberculosis

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Coinfection is the simultaneous infection of a host by multiple pathogen species. In virology, coinfection includes simultaneous infection of a single cell by two or more virus particles. An example is the coinfection of liver cells with hepatitis B virus and hepatitis D virus, which can arise incrementally by initial infection followed by superinfection.

Helminthiasis Macroparasitic disease in which a part of the body is infected with parasitic worms

Helminthiasis, also known as worm infection, is any macroparasitic disease of humans and other animals in which a part of the body is infected with parasitic worms, known as helminths. There are numerous species of these parasites, which are broadly classified into tapeworms, flukes, and roundworms. They often live in the gastrointestinal tract of their hosts, but they may also burrow into other organs, where they induce physiological damage.

Opportunistic infection Infection caused by pathogens that take advantage of an opportunity not normally available

An opportunistic infection is an infection caused by pathogens that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune system, an altered microbiome, or breached integumentary barriers. Many of these pathogens do not cause disease in a healthy host that has a non-compromised immune system, and can, in some cases, act as commensals until the balance of the immune system is disrupted. Opportunistic infections can also be attributed to pathogens that cause mild illness in healthy individuals but lead to more serious illness when given the opportunity to take advantage of an immunocompromised host.

Helminthic therapy Deliberate infestation with parasitic worms

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Andrew F. Read

Andrew Fraser Read FRS is Evan Pugh professor of biology and entomology in the Center for Infectious Disease Dynamics (CIDD) at Pennsylvania State University.

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