MBI 111 - Definitions 1

Definitions

Host

An organism that provides essential nutrients and a suitable environment for another organism, such as a parasite, to live and grow.

Parasite

An organism that thrives on or in another organism (the host), derives nourishment from it, and potentially harms the host in the process; typically smaller than the host.

Disease

A condition characterized by disruption of normal physiological functions in the host, leading to detectable changes in health.

Symptom

Subjective indications of damage or distress experienced by the host, such as pain or fatigue, which are reported by the individual but not measurable by others.

Sign

Objective evidence of damage or disease in the host that can be observed or measured by others, such as a fever or rash.

Infectious disease

A type of disease in which harmful changes in the host's health result from the damage inflicted by a parasitic organism.

Pathogen

Any microorganism, including viruses, bacteria, fungi, and parasites, that is capable of causing disease in its host.

Virulence

A measure of the severity or harmfulness of a pathogen, indicating its ability to cause disease.

Virulent

Describes microorganisms that have a high propensity for causing disease, often requiring only a small number to establish an infection.

Attenuated

Refers to microorganisms that have lost some of their virulence, making them less capable of causing disease.

Avirulent

Describes microorganisms that do not cause disease in healthy hosts.

Opportunistic

Microorganisms that typically do not cause disease in healthy individuals but can lead to infections if introduced to unusual sites or if the host's immune system is compromised.

Koch's Postulates

A series of principles used to establish a causal relationship between a microorganism and a disease.

Present in every case of the disease

The microorganism must be found in all instances of the disease, though it may or may not be present in healthy individuals.

Isolated and grown in pure culture

The microorganism should be able to be isolated from an infected host and cultured independently in the laboratory.

Able to cause the disease when pure culture is inoculated into a healthy host

The microorganism must be capable of inducing disease when introduced into a healthy host.

Re-isolated from the host inoculated with pure culture

The microorganism must be recoverable from the experimentally infected host, confirming its role as a causative agent.

Steps in Pathogenesis

The sequence of events that a pathogen follows to cause disease in a host.

Contact the host

The pathogen must be capable of reaching and entering the host organism.

Colonize the host

The pathogen must attach to host cells or tissues and multiply successfully.

Infect the host

The pathogen must proliferate within the cells or tissues of the host to establish an infection.

Evade the host defense system

The pathogen must develop mechanisms to bypass the host's immune defenses.

Damage host tissues

The pathogen must cause harm to host tissues, which can occur through mechanical disruption or the release of harmful substances.

Virulence Factors

Specific traits or components of a microorganism that enhance its pathogenicity and enable it to cause disease.

Adhesins

Molecules that allow parasites to adhere to host cells, facilitating colonization.

Invasins

Substances that aid parasites in penetrating host cells or tissues.

Evasins

Factors that enable parasites to evade or resist the host's immune responses.

Toxins

Biologically active substances produced by parasites that can damage host cells or interfere with normal physiological processes.