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Reservoirs (Definitions (Contagious
-When the infectious agent is…
Reservoirs
Definitions
Contagious
-When the infectious agent is highly transmissible, especially through direct contact
Communicable
-When an infected host can transmit the infectious agent to another host & establish infection in that host
Non-communicable
-When an infectious disease does not arise through transmission of the infectious agent from host to host
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Nosocomial Infections
-Infectious diseases acquired as a result of a hospital stay
-Can be as low as 0.1% or as high as 20&; average is approx. 5%
-Most common infections involve the GU & respiratory tracts + surgical incisions
Acquisition
-Can happen directly or indirectly from fomites, medical equipment, other patients, medical personnel, visitors, air or H2O
-Indwelling devices form a ready portal of entry & habitat for infectious agents
Prevention
-Surgical asepsis = High level of disinfection, antisepsis & sterilization
-Medical asepsis = Any practice that lowers the load of infectious microbes in patients, personnel & the hospital environment
Examples -Gram-negative:
-Gram-positive:
- Staphylococci
- Streptococci
Living
Carrier
-An individual who inconspicuously shelters a pathogen & spreads it to others w/o any notice
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Chronic
-An individual who shelters the infectious agent for a long period after recovery due to the latency of the infectious agent
Passive
-Usually medical/dental personnel who constantly handle heavily contaminated materials which pose risk for accidentally transferring pathogens to patients
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Transmission
Modes
Indirect
-Infectious agent must pass from an infected host to an intermediate conveyor & from there to another host
-Transmitter can either be openly infected or a carrier
Vehicle
-Any inanimate material commonly used by humans that can transmit infectious agents
-Examples are food, water, biological products & fomites (Any inanimate object that harbours & transmits pathogens)
-Source of agent can be the soil, the handler or a mechanical vector
Airborne
-Indoor air can serve as an important medium for the suspension & dispersal of certain respiratory pathogens
-Droplet nuclei = Dried microscopic residues created when microscopic pellets of mucous & saliva are ejected from the mouth & nose
-Aerosols = Suspensions of fine dust/posture particles in the air that contain live pathogens
Direct
-Must have direct contact between the skin/mucous membranes
-Portal of exit meets portal of entry w/o the involvement of an intermediate object/substance
-Also includes droplets sprayed directly upon a person, but not droplet nuclei which can be suspended in the air
Patterns
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Vertical
-Transmission from parent to offspring via the ovum, sperm, placenta or milk
Description
-The primary habitat in the natural world from which the pathogen originates
-Often a human/animal carrier, but can also be soil, water, or plants
-Source = The individual/object from which infection is actually acquired
-Source can be the same as the reservoir (Ex. In syphilis, the source & the reservoir = the human body)
-Source can also be different from the reservoir (Ex. In hepatitis A, the source = contaminated food; the reservoir = human carrier)
Non-living -Soil & natural H2O bodies can harbour vegetative forms of bacteria, protozoa, helminths & fungi-Bacteria examples:
- Anthrax Bacillus
- Clostridium
-Fungi examples:
-Helminth example:
-Pathogens in natural H2O bodies:
- Legionella
- Cryptosporidium
- Giardia
Koch's Postulates
-A series of proofs that established the principal criteria for etiologic studies
-Direct investigators to:
1) Find evidence about a particular microbe in every case of a disease
2) Isolate the microbe & cultivate it artificially
3) Inoculate a healthy subject w/ the laboratory isolate & observe the resultant disease
4) Reisolate the agent from the subject
-Each isolated culture must be pure, observed microscopically & identified by means of characteristic tests
-First & second isolate must be identical
-Pathological effects, signs & symptoms of the disease in the 1st & 2nd subject must be the same