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micro #13 infection & disease


is a disturbance in the equilibrium resulting in pathogenic microbes multiplying in the tissues.


is the pathologic state that results when the infection damages or disrupts tissues and organs

infectious disease

the disruption of a tissue or organ caused by microbes or their products


are microbes that are present on the body for a period of and rapidly lost (not infection)


being used to identify the microbial profile inside and on humans
Human Microbiome Project

microbial antagonism

human host benefits from bacterial biota. Biota can produce vitamins, help digest lactose or prevent the overgrowth of harmful microorganisms by releasing bacteriocins


chemicals released by one microbe that inhibit other microbes

endogenous infections

caused by biota that are already present in the body


Natural part of the bacterial flora in the human body and have a symbiotic bacteria-host relationship with humans.


a microbe whose relationship with its host is parasitic and results in infection and disease


Type and severity of infection depend on pathogenicity of the organism and the condition of its host. how virulant is it, does it reproduce quickly?

True pathogens

capable of causing disease in healthy persons with normal immune system

opportunistic pathogens

cause disease when defenses are compromised (host said to be immunocompromised)


1. The degree of pathogenicity
2. Determined by its ability to
A. establish itself in the host
B. cause damage

virulence factor

any characteristic or structure of the microbe that contributes to its virulence (contributes to establishment or ability to cause disease)


coming from the outside.
ex. another person, desk, animal


already existing on or in the body (normal biota or latent infection)
infectious agent comes from the body

Infections by birth canal (TORCH)

1. toxoplasmosis
2. other diseases (hepatitis, HIV, clamidia)
3. Rubella
4. Cytomeglovirus (mumps)
5. Herpes complex

Becoming established: 3 steps

1. portals of entry (skin, gastrointestinal, respiratory, urogenital) - outside environment
2. Attaching to the host (adhesion) - fimbrae, surface proteins, adhesive slimes or capsules.
3. Surviving host defenses (phagocytes, some use anti-phagocytic factors

antiphagocytic factors

used by some pathogens to avoid phagocytes

antiphagocytic factors: Leukocidins

toxic to white blood cells, produced by Streptococcus and Staphylococcus

antiphagocytic factors: Extracellular Enzymes

Break down and inflict damage on tissues or dissolve the host's defense barriers
ex. mucinase, keratinase, collagenase. some react with components of blood

Bacterial Toxins

Specific chemical product that is poisonous to other organisms


the power to produce toxins


a variety of diseases caused by toxigenicity


toxinoses in which the toxin is spread by the blood from the site of infection (tetanus and diphtheria)


toxinoses caused by ingestion of toxins (botulism)


gram negative only, lipopolysaccharides


accumulated damage leads to cell and tissue death


any objective evidence of disease as noted by an observer


the subjective evidence of disease as sensed by the patient


when a disease can be identified or defined by a certain complex of signs and symptoms

Signs and Symptoms of Inflammation

Fever, pain, soreness, swelling


accumulation of fluids in afflicted tissue

Granulomas and abscesses

walled off collections of inflammatory cells and microbes in the tissues


swollen lymph nodes


the site of infection or disease


increase in WBC


a decrease in the number of WBCs


general state in which microorganisms are multiplying in the blood and are present in large numbers

Bacteremia or viremia

microbes are present in the blood but are not necessarily multiplying


primary habitat in the natural world from which a pathogen originates (can be inanimate)


the individual or object from which an infection is actually acquired


an individual who inconspicuously shelters a pathogen and spreads it to others without any notice


a live animal that transmits an infectious agent from one host to another
Majority are arthropods
Larger animals can also be vectors

Biological vector

actively participates in a pathogen's life cycle. (ex. mosquito, bites, feces, regurgitate blood)
some of part of life cycle of MO takes place

Mechanical vectors

transport the infectious agent without being infected (ex. flies)


an infection indigenous to animals but naturally transmissible to humans
ex. rabies, yellow fever

Communicable disease

when an infected host can transmit the infectious agent to another host and establish infection in that host
Transmission can be direct or indirect
Contagious agent: highly communicable

Noncommunicable disease

1. does not arise through transmission of the infectious agent from host to host
2. Acquired through some other, special circumstance (ex. cut)
3. Compromised person invaded by his or her own microbiota
4. Individual has accidental contact with a microbe in a nonliving reservoir

AB toxins

target organs

indirect transmission

1. Vehicle: any inanimate material commonly used by humans that can transmit infectious agents (food, water, biological products, fomites)
- Contaminated objects (doorknobs, telephones, etc.)
- Food poisoning
- Oral-fecal route
2. Air as a vehicle
- Indoor air
- Droplet nuclei
- Aerosols

Nosocomial infections

infectious diseases acquired or developed during a hospital stay

Etiologic agent

the causative agent

Robert Koch

developed a standard for determining causation that would stand the test of scientific scrutiny

Koch's Postulates

1. Find evidence of a particular microbe in every case of a disease
2. Isolate that microbe from an infected subject and cultivate it in pure culture in the laboratory
3. Inoculate a susceptible healthy subject with the laboratory isolate and observe the same resultant disease
4. Reisolate the agent from this subject


study the outbreak of the disease


total number of existing cases w/ respect to the population
= (total number of cases in population / total number of persons in population) x 100 = %


the number of new cases over a period of time
= number of new cases / total number of susceptible persons

mortality rate

the total number of deaths in a population due to a certain disease

morbidity rate

the number of persons afflicted with infectious diseases


disease that exhibitsa a relatively steady frequency over a long time period in a particular geographic locale (ex. lyme disease = found where ticks are located)


occasional cases are reported at irregular intervals in random locales


revalence of an endemic or sporadic disease is increasing beyond expectations. clusters of breakouts


spreada of an epidemic across continents

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