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Mode of transmission

route or method of transfer by which a pathogen travels from one host to the next

Reservoir

place where a pathogen lives or reproduces- may be a host or carrier, or a substance

Portal of entry

Where a pathogen enters a host - usually a respiratory tract, gastrointestinal tract, genitourinary tract or the skin

Incubation period

Time between entry of pathogen and onset of symptoms

Infectious/contagious period

Period of time when a host can transmit the disease to others

Portal of exit

Where a pathogen exits one host and is transmitted to another. Often the same as the portal of entry

Zoonotic diseases

Jumped from animals to humans - major health problem because of our close relationship to animals

Direct transmission def

Spread of disease from one organism to another without an intermediate organism

Direct contact

skin to skin contact

Types of indirect contact

Objects, droplets, airborne, foodborne, waterborne, animals, bodily fluids

Object transmission

Contaminated items

Droplets transmission

tiny droplets of mucous containing pathogens expelled during a cough or sneeze

Airborne transmission

dust or droplet nuclei containing pathogens may be suspended in the air for long periods of time, and may be inhaled

Waterborne transmission

Water supply can become contaminated due to lack of purification, or mixing of drinking and sewage water.

foodborne transmission

Food can become contaminated due to unhygienic food handling or storage

Animal transmission

contact with infected faeces, nasal secretions, or secretions through the mouth or eyes

Bodily fluid transmission

Saliva, urine, faeces, breastmilk, semen, vaginal secretions or blood can be passed from one person to another through cuts or abrasions, or through mucous membranes of mouth and eyes.

Vector def

carrier of disease

mechanical vector def

Vector is physically contaminated with the pathogen, only serves to carry the pathogen to the host

Biological vector def

Vector is intermediate host of the pathogen, is required for part of the life cycle of the pathogen

The germ theory of disease

Microorganisms are the cause of many diseases

Louis Pasteur swan-necked flask experiment

Hypothesised that spores carried in the air grow into microorganisms if nutrients are available Swan-necked flask experiment = flasks allowed air in but not dust and spores (got trapped in neck) In these flasks, meat broth which had been boiled did not spoil. In flasks open to the air, the broth did spoil. Disproved spontaneous generation

Louis Pasteur inventing pasteurisation

While working in wine industry, discovered presence of bacteria made wine, milk and other food spoil. Invented pasteurisation - boiling at 50-60 degrees , prevents stuff from going sour

Louis Pasteur vaccination of chickens

inoculated chickens with attenuated (dead or harmless) form of the bacteria that causes chicken cholera, demonstrated these chickens became resistant to the fully virulent strain

Robert koch contributions

First person to separate different bacteria and grow them as pure culturesWhen he grew different microorganisms on agar, they formed separate, isolated colonies- in this way microorganisms could be separated and distinguished from one anotherStudied anthrax - isolated bacillus anthracis from blood of a diseased organism, grew it and observed it. Showed this bacterium was always present in diseased organisms. Separated bacteria from blood, injected it into a healthy organism, which also developed the disease. Showed a specific disease could be caused by a specific microorganism

Koch’s postulates

Koch’s Postulates - how to conclusively determine a microorganism causes a disease Microorganism must be present in every organism with the diseaseMust then be isolated from the host and grown in a pure cultureWhen this pure strain is inoculated into a healthy animal, animal should develop the same diseaseSame microorganism must be able to be isolated from this second hostSecond culture must be identical to the first

Impact of Koch’s work

Once it was established disease could be caused by organisms outside the body, ways to control diseases and ways to preserve food were developedAs a result of Koch’s work, Pasteur began researching anthrax. He showed that sheep inoculated with an attenuated strain of the disease survived a virulent strain, where those not inoculated did not.

How do pathogens ensure continuity of species

pathogens must infect new hosts.

Types of adaptations of pathogens which facilitate their entry into a host`

Using a vector Antigenic variation attachment to host cells Production of microscopic spores Flagella and secretions Altering the behaviour of the host Symptoms of infection

Adaptation using a vector

To help them enter the bloodstream of their new host`

Adaptation antigenic variation

some pathogens alter their antigens, markers on their surface that the immune system recognises, to avoid immune response

Adaptation attachment to host cells

Intracellular pathogens need to bind to receptor molecules on the surface of host cells. Viruses have surface molecules complementary to those on the host cells- once they attach the cell engulfs them by endocytosis. Digesting the capsid exposes the nucleic acid core so the virus can replicate

Adaptation production of microscopic spores

Spores can spread easily through the air thanks to their small size

Adaptation flagella and secretions

Stomach is hard to survive in - flagella let pathogen move through viscous environment, secrete chemicals which neutralise stomach acid

Adaptation altering the behaviour of the host

Changes behaviour to move between hosts in different parts of the pathogen’s life cycle

Immunity def

a person’s ability to resist infection by an invading pathogen

Innate immunity def

first and second lines of defence- the lines present at birth

Adaptive immunity def

third line of defence - created in response to an antigen, either through natural exposure or vaccination

For the body to defend against pathogens… (recognition of self)

it must be able to recognise its own tissue and normal microflora that inhibit the body.

Major histocompatibility complex (MHC)

Cluster of tightly linked genes on chromosome 6 - code for MHC protein molecules attached to the surface of body cells. Used to differentiate between foreign and non-foreign materials.

MHC I molecules location

Surface of all body cells

MHC II molecules location

restricted to certain white blood cells, including macrophages and B-lymphocytes

Antigen def

molecule that is recognised as non-self. May be part of the pathogen itself, or a toxic secretion by the pathogen. Trigger an immune response in the body

First line of defence barrier types

Physical, chemical and microbiological barriers

Physical barrier types

Epithelial cells, mucous secreting membranes

Chemical barrier types

Secretions, Stomach acid and digestive enzymes, fluid in the lungs, defensins

Epithelial cells

line the skin, respiratory, gastrointestinal and urogenital tracts. Joined tightly by specialised membrane proteins which form a continuous barrier against pathogens

Mucous secreting membranes

trap invading organisms in mucous, membranes lined with cilia sweep the pathogens away

Secretions (chemical barriers)

Tears, sweat, saliva, and earwax contain lysozyme enzymes and antimicrobial agents that destroy microorganisms

Stomach acid and digestive enzymes (chemical barriers)

Kill pathogens in food

Fluid in the lungs (chemical barriers)

Contain proteins that coat pathogens, making it easier for them to be killed by macrophages

Defensins

Antimicrobial peptides, important in early protection of the lungs and digestive tract

Microbacterial barrier types

Microflora

Microflora (microbacterial barrier)

Non pathogenic organisms, present in healthy organisms. Prevent growth of pathogens by competing with them for space and resources, or by secreting chemicals

Second line of defence

Non specific - acts against all pathogens regardless of their nature

What does the second line of defence include

lymphatic system, phagocytosis, cell death, inflammation, fever and antimicrobial substances

The lymphatic system

System of vessels that carries a colourless fluid called lymph.

What occurs in the lymphatic system

Blood enters the capillaries under high pressure, forcing the fluid into spaces between cellsThe lymph drains into the lymphatic vessels, which run parallel to veinsFluid travels through the lymph vessels, then they empty into veins before they reach the heartThe fluid is filtered by lymph nodes, and the trapped cells are destroyed by macrophages by phagocytosis, or B cells produce antibodies

Lymph nodes

Located along lymphatic vessels- act as filters, removing microbes, foreign particles and dead cells from circulation

Tonsils

Collection of lymphatic nodes at the back of the throat- produce lymphocytes and antibodies

Thymus gland

Two lobed organ near the heart which produces T cells that destroy invading microbes directly or indirectly by producing toxins

Spleen

Largest mass of lymphatic tissue in the body. Stores and releases blood in case of demand. produces mature B cells, destroy bacteria by phagocytosis

Bone marrow

Produces red blood cells and many kinds of leucocytes- monocytes, macrophages, neutrophils eosinophils, basophils, and lymphocytes (B cells and T cells)

Leucocytes

B cells and T cells

Macrophage

Large, phagocytic cells

Phagocytes purpose

Clear away cell debris by leaving the capillaries and phagocytising (engulfing) foreign material

Macrophages location

Rest in tissues such as the liver, spleen, lymph glands and bone marrow

Neutrophils location

Circulate in the blood

Dendritic cells

Present in lymphatic tissue and the skin

Phagocyte types

Macrophages, neutrophils, dendritic cells

Phagocyte process

Detection - Phagocyte recognises microbe by chemicals and sticks to its surfaceIngestion - Microbe engulfed when phagocyte forms a vesicle around itPhagosome forms, encloses the microbes in a membraneFusion with lysosomeDigestion - the microbes are broken down by enzymesDischarge - Indigestible material is discharged by the cell

Cell death to seal off pathogens def

Body may seal off a pathogen with a cyst or a cluster of cells

Cell death to seal of pathogens process

Central core of dead tissue is surrounded with layers of macrophages, then lymphocytes, then fibroblasts (type of structural cell in connective tissue) This produces a tough outer wall that seals off the pathogen.

Collection of cells involved in cell death to seal of pathogens name

granuloma

Inflammation def

tissues invaded by a pathogen become red, hot, swollen and painful.

Chemokines

Released by damaged cells. Type of leucocyte called a mast cell

What does the skin release when damaged

platelets release proteins that form clots and lessen the bleeding.

What do chemokines release

Prostaglandins and histamines

What do histamine and prostaglandins cause (inflammation)

dilation of blood vessels near the site and increase permeability of the capillaries. Prostaglandins also inhibit aggregation of blood platelets, allowing more blood to flow and more fluid and phagocytes to pass through the vessel walls, causing swelling.

Inflammation overall purpose

confines the infection to one area and brings more phagocytes to the region, which then destroy and remove the cause of the infection.

Inflammation three stages

Increased diameter and permeability of blood vessels increases blood flow to the areaPhagocyte migration and phagocytosis destroys invading microbesTissue repair creates new tissue to replace dead or damaged cells

Normal body temp

36.2-37.2 degrees

When a macrophage destroys a pathogen… (fever)

It releases the protein interleukin-1

What does interleukin-2 do

Makes the hypothalamus release prostaglandins, which increase body temperature

Fever onset phase

Brings body up to temp - blood vessel constriction, increased metabolic rate, shivering

Chill phase of fever

Skin remains cold and shivering occurs

Crisis phase of fever

Body temp is maintained at the higher temp until interleukin-1 is eliminated. Sweating and vasodilation (heat losing mechanisms) occur and the person feels warm

Fever purpose

Makes the body a less favourable environment for bacteria and virus replication, which are temperature sensitive Also intensifies the effect of interferon (antiviral protein), believed to inhibit the growth of viruses and bacteria Increases metabolic processes- tissues repair themselves quicker Increases heart rate so white blood cells are carried to the site of infection faster

Third line of defence

Called specific immune response, because the response is based on interactions between specific immune system cells and specific antigens.

Antibodies

Globular proteins that bind to a specific antigen and mark it for elimination They have an antigen binding site which is specific to one antigen

Where are antibodies produced

produced in the lymph nodes by plasma B cells

Surface antibodies

Attached to B cells

Secreted antibodies

In the blood

Antibody-antigen complex

Antibody binds to antigens

What does formation of the antibody antigen complex do

Cause the release of a series of proteins called a complement that result in the bacteria being ingested and destroyed. Also causes the release of histamine, causing inflammation

Your body produces an antibody for….

Every antigen is encounters in its life

B cells are a type of

Lymphocyte

Where to B cells form, mature and develop

In the bone marrow (BBBBBBBBB cell)

What do b cells control

the antibody mediated response

antibody mediated response

targets pathogen directly, do not attack hosts infected cells