article : Symbiotic Relationships

Symbiotic Relationship	Living Apart (Not Interacting) Organism Organism A B	Living Together (Interacting) Organism Organism A B	Population Effects
Neutralism	0 0	0 0	Neither population affected

Competition

0 0

- -

Elimination of population most affected

Mutualism

- -

+ +

Populations must interact

Commensalism

- 0

+ 0

A must interact; B not affected

Parasitism

- 0

+ -

A (Parasite) must interact; B (Host) negatively affected

Designed & Maintained by David M. Rollins
Copyright © 2000, D.M. Rollins and S.W. Joseph
Revised: September 2003
URL: http://life.umd.edu

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article : Host-Parasite Interaction Basic Definitions

INDEPENDENCE:

living free from the influence, guidance, or control by another organism

SYMBIOSIS:

a relationship in which two dissimilar organisms (SYMBIOTES, SYMBIONTS) live in close association with one another

MUTUALISM:

mutually beneficial relationship between two species

COMMENSALISM:

a relationship between two species in which one is benefited and the other is not affected, neither negatively nor positively

PARASITISM:

a relationship between two species in which one benefits (parasite) from the other (host); usually involves some detriment to the host

BENIGN:

referring to a non-life or non-health threatening condition = COMMENSALISM

MALIGNANT:

a disease tending to become progressively worse (MORBIDITY=illness) and potentially result in death (MORTALITY=death)

CARRIER:

a symptomless individual who is host to a pathogenic microorganims and who has the potential to pass the pathogen to others

PATHOGENICITY:

the quality of producing or the ability to produce pathologic changes or disease

VIRULENCE:

a measure of pathogenicity; a measurement of the degree of disease producing ability of a microorganism as indicated by the severity of the disease produced; a measure of the dosage required to caused a specific degree of pathogenicity --- one general standard is the LD50

DOSAGE:

the number of pathogenic microorganisms entering the host

LD50:

the number of microorganisms required to cause lethality in 50% of the test host

TRUE PATHOGEN:

any microorganism capable of causing disease; an infecting agent

OPPORTUNISTIC PATHOGEN:

a usually harmless microorganism that becomes pathogenic under favorable conditions

INFECTION:

the colonization and/or invasion and multiplication of pathogenic microrganisms in the host with or without the manifestation of disease

COLONIZATION:

the successful occupation of a new habitat by a species not normally found in this niche

MULTIPLICATION:

the ability of a microorganism to reproduce during an infection

DISEASE:

an abnormal condition of body function(s) or structure that is considered to be harmful to the affected individual (host); any deviation from or interruption of the normal structure or function of any part, organ, or system of the body

Designed & Maintained by David M. Rollins
Copyright © 2000, D.M. Rollins and S.W. Joseph
Revised: September 2003
URL: http://life.umd.edu

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article : Koch's Postulates to Identify the Causative Agent of an Infectious Disease

Koch's Postulates

Four criteria that were established by Robert Koch to identify the causative agent of a particular disease, these include:

1. the microorganism or other pathogen must be present in all cases of the disease



2. the pathogen can be isolated from the diseased host and grown in pure culture



3. the pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal



4. the pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen

Designed & Maintained by David M. Rollins
Copyright © 2000, D.M. Rollins and S.W. Joseph
Revised: September 2003
URL: http://life.umd.edu/

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article : Disease Triad

Designed & Maintained by David M. Rollins
Copyright © 2000, D.M. Rollins and S.W. Joseph
Revised: September 2003
URL: http://life.umd.edu

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article : Schick Test

Schick Test: The intracutaneous skin test introduced by Schick in 1913 that enables us to distinguish between individuals who are susceptible and those who are resistant (i.e., immune) to diphtheria toxin and to test for sensitivity to toxoid. The test is based on the following empirical findings:

1. Intracutaneous injection of 1/50 MLD (minimal lethal dose) (for a guinea pig) of diphtheria toxin produces a strong, but tolerable, reaction in individuals having no antitoxin.



2. Individuals having 1/30 unit or more of antitoxin per ml of blood neutralize this test dose and show no reaction. Such individuals are also usually resistant to diphtheria.

REACTIONS TO SCHICK TEST

	TOXIN		TOXOID
SKIN RESPONSE	36 h	120 h	36 h	120 h	INTERPRETATION
POSITIVE REACTION	-	+	-	-	Nonimmune, Nonsensitive
NEGATIVE REACTION	-	-	-	-	Immune, Nonsensitive
PSEUDO REACTION	+	-	+	-	Immune, Sensitive
COMBINED REACTION	+	+	+	-	Nonimmune, Sensitive

Designed & Maintained by David M. Rollins
Copyright © 2000, D.M. Rollins and S.W. Joseph
Revised: August 2000
URL: http://life.umd.edu

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