infectious disease Flashcards
Immune System Lines of Defense
The immune system includes three lines of defense against foreign invaders: physical and chemical barriers, nonspecific resistance, and specific resistance.
The first line of defense are the physical and chemical barriers, which are considered functions of innate immunity.
The second line of defense is nonspecific resistance, which also is considered a function of innate immunity.
The third line of defense is specific resistance, which is considered a function of acquired immunity.
Types of direct contact
- person-to-person contact
Occurs when an infected individual touches or exchanges body fluids with another individual. This includes touching, kissing,
sexual contact, biting and contact with oral secretions or body lesions, e.g. herpes, gonorrhoea, HIV, chickenpox and measles. - droplet spread
The result of droplets spray caused by talking, coughing and sneezing. Travels a short distance before settling.
e.g. influenza, chickenpox, measles, tuberculosis.
Types of indirect contact
- airborne transmission
Some pathogens can remain suspended in the air for many hours outside of the body. They can travel long distances and infect an
individual long after the original host has left the area. E.g. cold and measles viruses. - contaminated objects
Transmission occurs when a surface or object containing the pathogen is touched and the pathogen is transferred to the mouth,
nose or eyes before washing the hands. - food and drinking water
Several pathogens are transmitted as a result of improper treatment, handling or storage of food and water. E.g. Vibrio cholerae
(cholera), escherichia coli (food poisoning, diarrhoea) - animal-to-person contact
Usually occurs from a scratch or bite from an infected animal or from handling of waste. E.g. toxoplasma gondii (toxoplasmosis)
is a protozoan parasite found in cat faeces, rabies virus (rabies). - vector-borne
A vector is an organism that is not the pathogen but can spread the disease from one host to another (carrier) (fleas, ticks etc, they
carry the disease (they aren’t affected) and spread the pathogen between hosts) e.g. if someone with malaria gets bitten by a
mosquito and then the mosquito goes and bites someone else, it passes on the malaria pathogen
Prion
NON-LIVING
Defective form of protein molecule Does not contain DNA or RNA Insert themselves into neurological tissue and mostly attacks brain or nerve cells Molecular level-low nm (very small) Not visible with light microscope Mad-cow disease Creutzfeldt-Jakob disease ( mad cow but in humans)
Virus
NON-LIVING Non-cellular Contains DNA, RNA and protective coat Requires a living host cell to replicate Less than 500nm Not visible with light microscope Hepatitis B - HBV AIDS - HIV Smallpox
Bacteria
LIVING Unicellular, prokaryotic organism (no membrane-enclosed organelles) Cell wall surrounding cell Up to 100um Visible with light microscope Tuberculosis Anthrax
Protozoa
LIVING Malaria (not by mosquitos themselves) Eukaryotic unicellular organisms Usually complex life cycle 50-150um Visible with light microscope Giardiasis caused by giardia lamblia
Fungi
LIVING Eukaryotic cells with cell wall Some unicellular, most are multicellular um to mm Tinea - Tinea corporis Thrush - candida albican
Macro-parasite
LIVING Eukaryotic cell - multicellular organism Mostly arthropods or worms External parasites = ectoparasites Internal parasites = endoparasites Mm to metres Visible with naked eye Tapeworm - malnutrition/diarrhea Paralysis tick - paralysis
Direct contact transmission
occurs when pathogens are transferred between individuals without a contaminated intermediate person, object, or environmental surface.1 For example, when blood or other potentially infectious materials from an infected person enters the body of a susceptible person through direct contact with mucous membrane or breaks in the skin, e.g., when pathogens are transferred from a patient to a HCP during ungloved contact with mucous membrane or skin.
Indirect contact transmission
occurs when pathogens are transferred between individuals via a contaminated intermediate person, object, or environmental surface.1 For example, when the hands of HCP become contaminated and hand hygiene is not performed prior to touching the next patient; when contaminated patient-care items are shared between patients without having been adequately cleaned, disinfected, or sterilized; or in association with contaminated sharps and needlestick injuries.
Vector transmission
occurs when a living organism carries an infectious agent on its body (mechanical) or as an infection host itself (biological), to a new host.
Vehicle transmission
occurs when a substance, such as soil, water, or air, carries an infectious agent to a new host.
Adaptations of pathogens for entry into host and also for transmission
Adaptations for transmission include:
Pathogen can attach to host using pili and fimbria and tis prevents them from being washed away by host, tears, secritions.
Pathogens release enzymes to breakdown cell contents
Pathogens- can be airborne, resist drying out this helps their transfer too other hosts
In waterborne pathogens, they can colonise water reservoirs, have flagella to elp them move, many are not destroyed with simple boiling.
Pathogens can form spores in soil and survive for long times.
WORK OF LOUIS PASTEUR
● Prior to Pasteur, it was believed life ‘spontaneously generated’. Pasteur predicted that this was incorrect and microbes were
present in the air and that food spoils when these microbes land and become active.
● Aimed to demonstrate that microbes were air-borne and did not spontaneously generate
● Swan-necked flask experiment: set up two swan necked flasks. Boiled nutrient broth in the two flasks in order to sterilise - kill any present microbes. One flask had its neck removed, exposing nutrient broth to air - this flask had bacterial growth. Through this he demonstrated that microbial growth was a result of particles in the air, and could not arise spontaneously in sterile environments
