Unit 3 AoS 2- INFECTION AND DISEASE Flashcards
Difference between a pathogen and a pathogenic agent?
Pathogens are cellular agents (bacteria, fungus, protozoans, parasites) whereas pathogenic agents refers to non-cellular agents (viruses, prions, viroids).
What are the 3 different shapes of bacteria?
Coccus (round-shaped), spirochaete (spiral-shaped) and bacillus (rod-shaped).
What is a vector?
An animal (usually an insect) that carries pathogens from one host to another and is not affected by it.
What is a parasite?
An organism that lives in or on a host organism, obtaining food and/or shelter, and contributing nothing to the host’s welfare. Not necessarily pathogenic. (Parasites don’t necessarily kill their hosts, as their food source would ultimately be destroyed).
What is an endoparasite?
Parasite that lives within the host (e.g. tapeworm)
What is an ectoparasite?
Parasite that lives on the surface of the host (e.g. flea)
What is a disease?
Any body abnormality or failure to function properly in an organism (such as incorrect metabolism, injury, infection) except that resulting directly from physical injury.
What is an infectious disease?
A disease caused by the invasion and growth of a pathogen within an organism and is contagious.
What is a non-infectious disease?
A disease caused by any other source than infection/ e.g. by the environment (UV light effect on skin cancer, cyanide poisoning), poor nutrition (scurvy, obesity), genetic disorders (cystic fibrosis, Huntington’s disease) etc.
What is a host?
The organism in or upon which a parasite feeds. In some life cycles, more than one host is required by the parasite species.
What is a primary host?
Organism where pathogen lives in the adult form and reproduces (usually shows disease sympoms)
What is a secondary (intermediate) host?
Organism in which the parasite passes through its larval or asexual stages only (e.g. sheep or human in hydatid tapeworm lifecycle).
What is a carrier?
An individual that is host to a pathogen, but does not experience signs or symptoms of infection, yet can transmit the disease to others.
What is an infection?
The invasion and growth of a harmful cellular/non-cellular agent within the body of a host.
How do bacteria replicate?
Bacteria reproduce asexually by binary fission.
What is a leucocyte?
White blood cell.
In what ways can an infectious disease be transmitted from individual to individual?
Direct contact Indirect contact Water Air Food Vectors
Examples of direct contact?
- Touching, kissing (e.g. measles, fungal infections, colds)
* Exchange of bodily fluids (e.g. AIDS, hepatitis)
Examples of indirect contact?
*Bed linen, contact with soil (e.g. diphtheria)
Examples of transmitted disease through consumption of contaminated water?
- Typhoid
* Cholera
Examples of transmitted disease through air droplets (ie sneezing, inhalation)?
- Influenza
- Pneumonia
- Chicken pox
Examples of transmitted disease through consumption of contaminated food?
- Salmonella
* Hepatitis
Examples of transmitted disease through vectors?
- Malaria (Mosquitoes)
* African Sleeping Sickness Trypanosome (Tsetse fly)
What is the difference between an infectious and a non-infectious disease?
An infectious disease is caused by a pathogen or pathogenic agent and can be passed on from one person to another, while a non-infectious disease cannot be passed on from one person to another and is caused by factors other than pathogens, e.g. dietary diseases, inherited diseases or exposure to mutagens.
Examples of pathogens?
- Bacteria
- Protozoa
- Fungi
Examples of pathogenic agents?
- Virus (protein coat surrounding RNA or DNA)
- Prion (protein)
- Viroid (small piece of RNA)
What is a viroid?
- Smallest known infectious agent
- Small piece of RNA (no protein)
- Only known pathogens found in plants such as potatoes, tomatoes and grape vines.
What is a prion?
A prion is an abnormal and infectious folded piece of protein.
Diseases caused by prions?
TSE (mad cow disease)
Scrapie (sheep)
Creutzfeldt- Jakob disease and kuru (humans)
What is a virus?
A particle lacking cellular organisation and consisting of genetic material (RNA/DNA) surrounded by a protein coat and only reproduces in a host cell.
Role/function of the bloodstream in the immune system?
Carries immune cells like phagocytes and other proteins like complement proteins, blood clotting proteins such as prothrombin and fibrinogen.
Role/function of non-self antigen in the immune system?
Form of identification to inform cells in the body that a foreign body has entered.
Role/function of self antigen (eg MHC marker) in the immune system?
Form of identification for self-cells- so that immune cells do not attack them.
Complement proteins
*Group of proteins that assist phagocytes in recognising pathogens (continually circulate in blood plasma)
*Help in bacterial infection by attracting phagocytes to site of infection.
*Bind to bacteria and lyse cell membrane, make it easier for bacteria to be recognised by phagocytes and call more phagocytes to the area
*They can also directly lyse the membrane of bacterial cell (NOT cell walls) causing leakage of cell contents in order
to attract more phagocytes to area
*Promote inflammation (by increasing local permeability of capillaries and attracting phagocytes)
Phagocyte
A white blood cell that is able to engulf and ingest foreign bodies.
Examples: macrophages, monocytes, neutrophils, eosinophils
Part of the non-specific immune response
Macrophage
A type of phagocyte. In the bloodstream, this cell is the monocyte and when it leaves the bloodstream, it matures into this cell.
Part of the non-speicific immune response
Dendritic cell
A type of phagocyte.
Interferons
Proteins released by virus-infected cells and immune cells which warn surrounding uninfected cells of virus and increase the resistance of the uninfected cells so that the virus remains outside the cell where it is more susceptible to phagocytosis.
T cells
Cells which are produced in bone marrow but mature in the thymus gland. They are important immune cells in third line of defence.
T helper cell
- Specialised lymphocyte that helps in recognising foreign antigen and stimulating the T cytotoxic cells and B cells.
- Regulatory cells that, when stimulated by antigen, produce and release cytokine molecules that control development and function of other T and B cells, and phagocytes
- Also release interferon.
Antigen presentation
Process where macrophage displays the foreign antigen on its cell membrane and presents it to the T helper cell to trigger 3rd line of defence.
1) Phagocyte engulfs and ingests pathogen
2) Parts of the pathogen (non-self antigen) goes to the surface of the phagocyte
3) The phagocyte presents the antigen to a T helper cell
4) T-helper cell is activated
T cytotoxic cells
Specialised lymphocyte that recognises and destroys viral infected cells, cancer cells and foreign eukaryotic cells (ie protists and fungi).
Cytotoxic T cells lyse infected cells with perforin and toxic granules to destroy the cell and its contents.
*The release of cytokines further stimulates phagocytosis by macrophages.
*Can also release interferon.
B cells
A lymphocyte that has a unique antibody that can recognise specific antigen
Antibody
An immunoglobin with two antigen-binding sites.
Immunoglobulin G (IgG)
A type of antibody
Clonal Selection/ Clonal Expansion/ Differentiation
When a B lymphocyte is triggered by the binding of the antigen (with the help of T helper cell), it is activated to form clones of cells, some of which become B plasma cells and some of which become B memory cells.
B memory cell
A lymphocyte that is produced during the first infection, to retain information about the pathogenic agent and it helps the body to ‘fight back’ even stronger and faster in subsequent infections.
B plasma cell
A type of lymphocyte that can produce massive amounts of antibodies
Antibody round- up/ Agglutination
- Agglutination occurs when an antibody-antigen complex forms–> attracts macrophages
- Process of gathering of antigens by the antibodies.
- Specific Antigens bind to the specific antibodies, which block antigens from binding to its target or attracts phagocytes/ macrophage
Tears/ Saliva
Contain the enzyme lysozyme which may cause the bacteria to lyse/burst and tears wash bacteria away from the body.
Sneezing
sneeze out bacteria
Mucus
Traps bacteria and stops them from entering into the body
Cilia
Filter air passing through respiratory system.
Guides pathogens trapped in mucus towards the nose/mouth.
Intact Skin
acts as a physical barrier to stop bacteria from entering body
Stomach acid
may kill bacteria– acid denatures proteins in cell membranes of bacteria
Platelets
Platelets clot blood.
- When they come into contact with damaged cells they release an enzyme called thromokinase (1 mark).
- This converts prothrombin to thrombin, which catalyses the conversion of fibrinogen to fibrin.
- Fibrin is an insoluble protein that traps blood cells (1 mark), causing a blood clot which plugs holes in tissues damaged as bacteria entered, or prevents bacteria from entering the body (1 mark)
What does the first line of defence include?
External barriers of the body, including:
- Intact skin (relatively tough and impermeable unless broken)
- Tears (contains lysozymes)
- Saliva (contains amylase)
- Mucus (traps micro- organisms)
- Sweat (acidic, dehydrating repellent)
- Nasal hair (filter air)
- Ear wax (traps pathogens)
- Cilia
- Stomach acid kills most pathogens that enter
- Blood clotting
Histamines
released from damaged tissues when bacteria enter the body –dilate blood vessels which brings more phagocytes/ macrophages to the area
Phagocyte
eg neutrophil/ monocyte
recognise non-self antigens on bacteria and engulf bacteria
Macrophage
- engulf bacteria in surrounding tissues as they recognise non-self antigens on the surface of the pathogens (1 mark) * may present antigens to THelper cell (Antigen Presenting Cell) (1 mark)
Inflammation
- Inflammation is triggered by histamines released from mast cells, platelets and cytokines from damaged cells
- Results in:
- increased blood flow to area (1 mark),
- increased permeability of blood vessels so phagocytes and macrophages can enter tissues to fight the bacteria, as well as antibodies and complement proteins (1 mark).
- Increased phagocytosis in area results in pus formation.
- Inflammation causes heat, swelling, pain and reduced movement.
- The stimulated macrophages release chemicals such as cytokines which affect the control of temperature by the hypothalamus, leading to fever.
Interferon
- Warns of viral infection to neighbouring uninfected cells, when infected cell is destroyed – not released with bacteria.
- Interferons also stimulate the production of antiviral proteins.
- A class of cytokines
Cytokines
- glycoproteins that act as signalling molecules (chemical messengers) in the immune system
- only act on cells locally with specific receptors
- released by cells after tissue injury or infection
- trigger both specific and non-specific responses such as:
- promote growth of lymphocytes,
- induce fever,
- activate macrophages,
- initiate inflammation,
- allow communication between cells involved with the immune system
Fever
- Fever is triggered by bacterial toxins ie pyrogens (toxins released by bacteria that act on the brain) and cytokines (released by stimulated macrophages which travel from blood to brain)
- released from macrophages (during inflammatory response)
- Increase in body temperature eg above 37.8ºC, resulting from the resetting of the body temperature set-point in the hypothalamus.
- higher temperature inhibits reproduction of most bacteria
- Increase in temperature increases enzyme activity improving the inflammatory response.
Natural Killer Cells
- Detect cancerous and virus-infected cells by changes in carbohydrate molecules on surface of body cells
- Lyse cell membranes of any virus infected cells (and microbial infection)
- Part of the non-specific immune response
What does the second line of defence include?
- Phagocytes (engulf invaders)
- Complement proteins (assist in identifying invading pathogens by coating bacterial cells, stimulating histamines and attract phagocytes).
- Inflammation (increase blood supply)
- Histamines (attract phagocytes)
- Natural killer cells (NK) (kill virus infected cells but non-specific)
- Interferon (makes uninfected cells more resistant to viruses)
- Fever
What is an antigen?
- A compound, usually a protein, that can trigger the immune system to respond in various ways, including antibody production
- Binds to specific antibodies
- Allows the body to distinguish from self and non-self
What are MHC markers?
MHC are the genes that code for the proteins on the cell membranes that act as “markers”. These proteins are called “MHC markers”.
It is the combination of antigens (proteins) on the outer surface of the cell membrane that are ‘self’
On what cells can Class 1 MHC markers be found?
All cells except red blood cells
On what cells can Class 2 MHC markers be found?
On immune cells such as T lymphocytes, B lymphocytes and some macrophages