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
WORK OF ROBERT KOCH
● Predicted that specific microscopic pathogen cause specific diseases.
● Isolated a suspected pathogen from a deceased animal. Cultured the pathogen in
growing medium, inoculated (infected) healthy animals with the suspected
pathogen. The healthy animals then died as a result of that pathogen being
introduced into the animal. Then took that same pathogen from the second
deceased animal and grew it in culture and found that it was the same as the
original cultured pathogen
Koch’s Postulates.
- The pathogen must be found in all animals suffering from the disease, but not in
healthy animals. - The pathogen must be isolated from a diseased animal and grown in pure culture
medium. - The cultured pathogen should cause disease of the same symptoms when
introduced into a healthy animal. - The pathogen must be re-isolated from the experimentally infected animal, and
must be the same as the original source pathogen.
Plant diseases
Plant diseases are typically caused by various fungi and bacteria, and can have large scale effects on agricultural production.
CASE STUDY: fire blight
Blight: generic term given to any plant disease that causes rapid browning and death of the plant tissues.
Transmission
● Infection results in tissue death and bacterial ooze droplets on infected tissue
● Spread to healthy plants through rain, wind, insects and pruning tools
● Difficult to contain
● Prevention is the best option for management as fire blight is difficult to contain
● On-farm biosecurity to prevent entry, establishment and spread of pests and diseases
● Ensuring all staff and visitors are instructed in and adhere to on-farm hygiene practices
Animals diseases
Animal diseases are typically caused by various viruses and bacteria and can have a large scale effect on agricultural production.
CASE STUDY: foot and mouth disease
● Highly contagious disease of cloven-hoofed animals including cattle, sheep, goats and pigs.
● Australia is free from FMD as a result of strict quarantine where all animal products are prevented from entering the country
● Australia’s off-farm beef and sheep meat industry is 17 billion dollars according to Meat and Livestock Australia
Effect
● Fevers and blisters in mouth and hooves of cattle, sheep, goats and pigs
● Leads to severe production losses
● Although infected animals recover, the disease often leaves them weakened and debilitated
● As a result, herds are destroyed - vital to prevent spread of disease to other herds
PLANT RESPONSES TO PATHOGENS.
Fungi
- Living- Eukaryotic heterotrophic organisms; cells with a cell wall
- Fungal plant pathogens generally secrete enzymes that are able to digest the plant cell wall and enter via the stomata and ‘steal’
nutrients from the surrounding cells. They can also inhibit cellular processes, including photosynthesis, water and nutrient uptake.
- Symptoms: chlorosis (yellowing of leaves due to insufficient chlorophyll), mosaic leaf pattern, crinkled leaves and growth
stunting
Virus
- Non-living, non-cellular
- Contains DNA, RNA and protective coat
- Require a host cell to replicate
- Spread via vectors due to their inability to pass through plant cell walls. They can cause isolated infections or spread throughout
the plant and can inhibit cellular processes, including photosynthesis, water and nutrient uptake.
- Symptoms: chlorosis, leaf and stem wilting and rusting, leaf blotching, leaf mildew.
Hygiene practices:
In order to control the spread of disease, pathogens must be prevented from coming into contact with new hosts or preventing infection in
new hosts.
Hygiene: is a set of practices performed to maintain good health and minimise the spread of pathogens. Good hygiene practices can be
personal, communal or food related.
Personal hygiene:
refers to practices that an individual performs to minimise the risk of infection.
- Frequent bathing
- Handwashing with soap (anti-microbial features) and water
- Correct respiratory hygiene when coughing and sneezing
Quarantine
A strict isolation imposed to prevent the spread of disease or unwanted animals or plants.
Quarantine prevents the entry and spread of diseases by:
1. Inspection (e.g. boarders coming into Australia or between states, fruit fly)
2. Regulation (what food products can enter or exit the country)
3. Restriction of movement (should an outbreak of disease occur)
4. Enforced destruction of diseased organisms
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Vaccination (or immunisation) is the process of making people resistant to infection caused by specific pathogens. They are very
effective at preventing future infections. The immunity provided is either active or passive, dependent on the source of the immunity.
Active Immunity
The vaccine typically contains a live-attenuated or inactivated version of the
pathogen, which therefore lead to no symptoms of the disease.
This leads to the production of antibodies and T and B memory cells specific to the
antigen providing long-term protection from the disease.
Live-attenuated examples include the measles, mumps and rubella (MMR) vaccine and chickenpox vaccines.
