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pathogen
a parasite capable of causing disease in a host
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host
any organism that harbors another organism
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symbiosis
an association between two (or more) species
"living together"
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mutualism
both members benefit from the relationship
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parasitism
one organism benefits from the relationship, where as the other organism
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commensialism
two species live together in a relationship such that one benefits and the other one neither benefits nor is harmed
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antagonism
both species harm each other without ether benefiting
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contamination
microorganisms are present
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infection
the multiplication of any parasitic organism within or on the host's body
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infestation
the presence of larger parasites, such as worms or arthropods, in or on the body
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disease
a disturbance in the state of health wherein the body cannot carryout all its normal functions
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pathogenicity
the capacity to produce disease
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virulence
the intensity of the disease produced by pathogens
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animal passage
the rapid transfer of the pathogen through animals of a species susceptible to infection by that pathogen
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attenuation
the weakening of the disease-producing ability of the pathogen
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transposal of virulence
a laboratory technique in which a pathogen is passed from its normal host to a new host species and then passed sequentially through many individuals of the new host species
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normal microflora
organisms that live on or in the body but do not cause disease
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resident microflora
comprise microbes that are always present on or in the human body
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transient microflora
microorganisms that can be present under certain conditions in any of the locations
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opportunists
organisms that do not usually cause disease but can do so under certain conditions
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conditions that create opportunities to cause disease:
- 1. Failure of the Host's Normal Defenses
- 2. Introduction of the Organisms into Unusual Body Site
- 3. Disturbances in the Normal Microflora
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Koch's Postulates
- 1. the specific causitive agent must be observed in every case of a disease
- 2. The agent must be isolated from a diseased host and must be grown in pure culture
- 3. when the agent from the pure culture is inoculate into healthy, but susceptible, experimental hosts, the agent must cause the same disease
- 4. The agent must be re-isolated from the inoculate, diseased experimental host and identified as being identical to the original specific causative agent
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Infectious disease
diseases caused by infectious agents such as bacteria, viruses, protozoa, and helminths
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noninfectious diseases
caused by any factor other than infectious organisms
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Inherited diseases
caused by errors in genetic information
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congenital diseases
structural and functional defects present at birth, caused by drugs, excessive X-ray exposure, or certain infections
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degenerative diseases
disorders that develop in one or more body systems as aging occurs
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nutritional deficiency diseases
lower resistance to infectious deseases and contribute to the severity of infections
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endocrine diseases
due to excesses or deficiencies of hormones
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mental disease
can be caused by a variety of factors, including those of an emotional, or psychogenic nature, as well as certain infections
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Immunological diseases
caused by malfunction of the immune system
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neoplastic diseases
involve abnormal cell growth that leads to the formation of various types of generally harmless, or cancerous growths or tumors
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Iatrogenic diseases
caused by medical preocedures and/or treatments
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Idiopathic diseases
diseases whose cause is unknown
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communicable infections diseases
some infections that can be spread from one host to another
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contagious diseases
highly communicable diseases
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Noncommunicable infectious diseases
are not spread from one host to another
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virulence factors
structural or physiological characteristics that help organisms cause infection and disease
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adherence
a critical point in the production of bacterial disease (attachment)
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adhesins
proteins or glycoproteins found on attachment pili (fimbrae) and capsules
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colonization
the growth of microorganisms on epithelial surfaces, such as skin or mucous membranes
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invasiveness
its ability to invade and grow in host tissues
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hyaluronidase
spreading factor
Streptococci produce this enzyme to digest hyaluronic acid
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coagulase
- a bacterial enzyme that accelerates the coagulation (clotting) of blood
- 1. keeps organisms from spreading
- 2. helps wall organisms off from immune defenses that might otherwise destroy them
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streptokinase
dissolves blood clots
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toxin
any substance that is poisonous to other organisms
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exotoxins
soluble substances secreted into host tissues
more powerful toxins produced by several Gram-positive and a few Gram-negative bacteria
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endotoxins
part of the cell wall and are released into host tissues from Gram-negative bacteria
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hemolysins
the action of these exotoxins is to lyse (rupture) red blood cells
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Alpha-hemolysins
hemolyze blood cells, partially break down hemoglobin, and produce a greenish ring around colonies
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beta-hemolysins
hemolyze blood cells but completely break down hemoglobin and leave a clear ring around colonies
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leukocidins
exotoxins produced by many bacteria
damage or destroy certain kinds of white blood cells called neutrophils and macrophages
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leukostatin
interferes with the ability of leukocytes to engulf microorganisms that secrete the exotoxin
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toxemia
the spreading of exotoxins by blood from the site of infection
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intoxications
disease that result from the ingestion of a toxin
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neurotoxins
are exotoxins that act on tissues of the nervous system to prevent muscle contraction (botulism) of muscle relaxation (tetanus)
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enterotoxins
are exotoxins that act on tissues of the gut
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toxoid
an altered toxin that has lost its ability to cause harm but that retains antigenicity
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cytopathic effect
in tissue culture systems, once inside a cell, viruses cause observable changes
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inclusion bodies
consist of nucleic acids and proteins not yet assembled into viruses, masses of viruses, or remnants of viruses
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productive infection
occurs when viruses enter a cell and produce infectious offspring
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abortive infection
occurs when viruses enter a cell but are unable to express all their genes to make infectious offspring
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latent viral infections
the virus may retreat into the nervous system and remain inactive, or latent
stress, other infections, or fever can reactivate the virus
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persistent viral infections
involve a continued production of viruses over many months or years
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mycotoxins
certain fungi parasites produce which cause disease in human
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sign
a characteristic of a disease that can be observed by examining the patient
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symptom
a characteristic of a disease that can be observed or felt only by the patient
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syndrome
combination of signs and symptoms that occur together and are indicative of a particular disease or abnormal condition
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leukocytosis
an increase in the number of white-blood cells circulating in the blood
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sequelae
some disease leave aftereffects, even after recovery
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acute disease
develops rapidly and runs its course quickly
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chronic disease
develops more slowly, is usually less severe, and persists for a long, indeterminate period
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latent disease
characterized by periods of inactivity
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focal infection
confined to a specific area, but pathogens, or their toxins, can spread to other areas
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systematic infection
generalized infection
affects most of the body, and the pathogens are widely distributed in many tissues
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primary infection
an intial infection in a previously healthy person (many are acute)
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secondary infection
follows a primary infection, especially in individuals weakened by the primary infection
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incubation period
the time between infection and the appearance of signs and symptoms
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prodromal phase
a short period during which nonspecific, often mild, symptoms such as malaise and headache sometimes appear
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prodrome
a symptom indicating the onset of a disease
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invasive phase
the period during which the individual experiences the typical signs and symptoms of the disease
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acme
when the signs and symptoms reach their greatest intensity
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pyrogens
- act on a center in the hypothalamus, referred to as the body's thermostat.
- Pyrogens set the thermostat at a higher-than-normal temperature
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decline phase
the period of illness during which host defenses and the effects of treatment finally overcome the pathogen
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convalescence period
tissues are repaired, healing takes place, and the body regains strength and recovers
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