4.1.1 communicable diseases, disease prevention and the immune system Flashcards
what is a communicable disease?
disease that can be passed from one organism to another, of same or different species
what is a pathogen?
a disease causing microorganisms
how are bacteria classified?
- by basic shape - rod shaped, spherical, comma shaped, spiralled, corkscrew
- by cell wall - Gram positive and Gram negative
what colour do Gram positive bacteria look under a light microscope after Gram staining?
purple-blue
what colour do Gram negative bacteria look under a light microscope after Gram staining?
red
what are viruses?
non-living infectious agents
viruses invade living cells, the genetic material takes over the host cell
what are types of pathogens?
bacteria
viruses
protoctista
fungi
what are parasites?
an organism that lives in or on another organism (host)
and gains nutrients from host at hosts expense
what are the modes of action of pathogens?
- damaging host tissues directly
- producing toxins which damage host tissues
how do pathogens damage host tissues directly?
- viruses take over cell metabolism - viral genetic material is inserted into host DNA, the virus uses host cell to make new viruses which burst out of cell then spread to infect other cells
- protoctista digest and use the cell contents as they reproduce
- fungi digest living cells and destroy them
how do pathogens damage host tissues with toxins?
- bacteria produce toxins damage host cells by breaking down cell membranes, inactivate/damage enzymes, interfere with host genetic material
- some fungi produce toxins which affect host cells
what are bacteriophages?
viruses that attack bacteria
what plant disease is caused by bacteria?
ring rot
what are the characteristics of ring rot?
damages leaves, tubers and fruit
what plant disease is caused by virus?
tobacco mosaic virus
what are the characteristics of tobacco mosaic virus?
damages leaves, flowers and fruit, stunting growth and reducing yields
what plant disease is caused by protoctist?
potato blight
what is black sigatoka?
what are the characteristics of black sigatoka?
a banana disease caused by fungus Mycosphaerella fijiensis, which attacks and destroys the leaves
the hyphae penetrate and digest cells, turning leaves black
what plant disease is caused by protoctist?
potato blight/ tomato blight/ late blight
what is potato blight?
what are the characteristics of potato blight?
- caused by protoctist oomycte Phytophthora infestans
- hyphae penetrate host cells, destroying leaves, tubers and fruit
what animal diseases are caused by bacteria?
- tuberculosis
- bacterial meningitis
what are the characteristics of tuberculosis?
damages and destroys lung tissue and suppresses the immune system
what are the characteristics of bacterial meningitis?
bacterial infection of the meninges of the brain which can spread to the rest of the body causing septicaemia and rapid death
what animal diseases are caused by viruses?
- HIV (human immunodeficiency virus)
- influenza
what are the characteristics of HIV?
targets T helper cells in the immune system
destroys the immune system so affected people are open to other infections
what are the characteristics of influenza?
viral infection of ciliated epithelial cells
kills cells, leaving airways open to secondary infection
what animal disease is caused by protoctista?
malaria
what are the characteristics of malaria?
caused by protoctista Plasmodium and spread by mosquitoes
the Plasmodium invades the red blood cells, liver and the brain
what animal diseases are caused by fungi?
- ring worm
- athlete’s foot
what are the characteristics of ring worm?
fungal disease affecting mammals
causes grey-white, crusty, infectious, circular areas of skin
what are the characteristics of athlete’s foot?
a human fungal disease caused by Tinia pedia
a form of human ring worm
digests skin on feet, causing cracking and scaling
what are some methods of direct transmission of pathogens between animals?
- direct contact - skin-to-skin, exchange if bodily fluids
- inoculation - break in skin, animal bite, puncture wound/ sharing needles
- ingestion - eating contaminated food/drink
what are some methods of indirect transmission of pathogens between animals?
- fomites - inanimate objects can transfer pathogens
- droplet infection
- vectors - mosquitoes, fleas, water
factors affecting the transmission of communicable diseases in animals (7)
- overcrowding living and working conditions
- poor nutrition
- compromised immune system
- poor disposal of waste
- climate change - new vectors/diseases
- culture and infrastructure - traditional medical practises
- socioeconomic factors - lack of health professionals
what are some methods of direct transmission of pathogens between plants?
direct contact of a healthy plant with a diseased plant
what are some methods of indirect transmission of pathogens between plants?
- soil contamination - infected plants leave pathogens or reproductive spores
- vectors - wind, water, animals, humans
factors affecting the transmission of communicable diseases in plants (5)
- planting varieties of crops that are susceptible to disease
- over-crowding
- poor mineral nutrition - reduces resistance
- damp, warm conditions increase the survival and spread of pathogens and spores
- climate change - increased rainfall/wind, changing conditions allow animal vectors
physical defences in plants
- cellulose cell wall
- waxy cuticle
- stomatal closure
- callose (polysaccharide)
- tylose formation
- necrosis
- canker
effect of callose
- deposited between cell walls and cell membrane in cells next to infected cells
- lignin added to callose to make barrier stronger
- callose blocks sieve plates - sealing off infected part of plant
- callose deposited in the plasmodesmata
effect of tylose formation
- swelling that fills xylem vessel
- prevents spread of pathogens
- tylose contains chemicals toxic to pathogens
what is necrosis?
- deliberate cell suicide of infected cells
- intracellular enzymes are activated by the injury
what is a canker?
a sunken necrotic lesion on the woody tissue - causes death of cambium tissue
chemical defences in plants
- insect repellents and insecticides
- defensins (defensive proteins) - cysteine rich proteins with antimicrobial action
- alkaloids - nitrogen containing compounds - bitter tasting, inhibit enzyme action, inhibit protein synthesis
- phenols - antibacterial/antifungal compounds, tannins -bitter taste, bind to digestive enzymes and inactivate them
- hydrolytic enzymes - chitinases (breaks down chitin), lysozymes (breaks down bacterial cell walls), glucanase (breaks down glycosidic bonds in glucose - anti-oomycete)
- terpenoids - essential oils with antibacterial/antifungal properties
primary non-specific defences in animals
- skin - barrier preventing entry of pathogens, produces sebum (antibacterial fatty acids) that inhibits growth of pathogens
- mucous membranes - mucus traps pathogens
- expulsive reflexes - cough, sneeze, vomit
- lysozymes in tears and urine
- hydrochloric acid in stomach
- blood clotting/wound repair
- inflammatory response
what is the inflammatory response?
- a localised response to pathogens
- mast cells are activated in damaged tissue and release histamines and cytokines
- histamines cause vasodilation - causing localised heat and redness
- histamines cause blood vessels to become more leaky - blood plasma is forced out causing swelling
- cytokines attract phagocytes to the site
how do blood clots form?
- when platelets come into contact with collagen in skin/blood vessel wall, they adhere and secrete substances
- thromboplastin - triggers a cascade of reaction, resulting in the formation of a blood clot
- serotonin - vasoconstriction - reduce blood supply to area
- clot dries forming scab
- epidermal cells below scab grow
- collagen fibres are deposited to strengthen tissue
secondary non-specific defences in animals
- fevers
- phagocytosis
how does fever defend against pathogens
- when a pathogen invades the body, cytokines stimulate hypothalamus to increase temperature
- high temperatures inhibit pathogen reproduction
- specific immune system works better at higher temperatures
what is phagocytosis?
the process by which phagocytes recognise non-self cells and digest them
what are the stages of phagocytosis?
NEUTROPHILS AND MACROPHAGES
- pathogens produce chemicals that attract phagocytes
- phagocytes recognise non-self proteins on the pathogen and binds to the pathogen
- phagocyte engulfs the pathogen and encloses it in a vesicle called a phagosome
- the phagosome combines with a lysosome to form a phagolysosome
- enzymes from the lysosome digest and destroy the pathogen
ONLY MACROPHAGES
- combines antigens from the pathogen surface membrane with glycoproteins in cytoplasm called major histocompatibility complex (MHC)
- MHC complex moves pathogen antigens to the macrophage’s own surface membrane, becoming an antigen-presenting cell
what do cytokines do?
- produced by phagocytes that have engulfed a pathogen
- act as cell-signalling molecules, stimulating other phagocytes to move move to the site of infection
- increase body temperature
- stimulate specific immune system
what do opsonins do?
- bind to pathogens so they are more easily recognised by phagocytes
- phagocytes have receptors on their cell membranes that bind to opsonins and the phagocyte then engulfs the pathogen
what are antibodies?
Y-shaped glycoproteins which bind to a specific antigen on a pathogen that has triggered an immune response
what is the structure on antibodies?
- two identical long polypeptide chains - heavy chains
- two shorter identical polypeptide chains - light chains
- chains held together by disulfide bridges
- hinge region - provides the antibody with flexibility, allowing it to bind to two antigens
- constant region - same in all antibodies
- variable region - the binding site which is different on different antibodies, specific to the antigen
what is formed when an antibody binds to an antigen?
antigen-antibody complex
how do antibodies work? (4)
- antibody of antigen-antibody complex acts as a opsonin - so complex is engulfed by phagocytes
- pathogen unable to invade cells when part of antigen-antibody complex
- antibodies act as agglutinins causing pathogens with antigen-antibody complexes to clump together
- antibodies can act as anti-toxins, binding to toxin produced by pathogens and making them ineffective
what are T lymphocytes?
lymphocytes that mature in the thymus gland
what are the types of T lymphocytes?
- T helper cells
- T killer cells
- T memory cells
- T regulator cells
what are B lymphocytes?
lymphocytes that mature in the bone marrow
what are the types of B lymphocytes?
- plasma cells
- B effector cells
- B memory cells
what do T helper cells do?
- have CD4 receptors on their cell-surface membranes on cell surface membrane which bind to antigens on APCs
- produce interleukins which stimulate the activity of B cells to increase antibody production, stimulates production of T cells and stimulates phagocytosis
what are interleukins?
a type of cytokine
what do T killer cells do?
- destroy pathogen carrying the antigen
- produce a chemical called perforin - perforin kills pathogen by making holes in the cell membrane
what do T memory cells do?
- part of immunological memory
- live for a long time
- if they meet an antigen a second time they divide rapidly to form a large number of clones of T killer cells
what do T regulator cells do?
- suppress the immune system to control and regulate it
- stop the immune response once a pathogen has been eliminated to prevent an autoimmune response
what do plasma cells do?
- produce antibodies to a particular antigen and release them into circulation
what do B effector cells do?
- divide to form plasma cell clones
what do B memory cells do?
- part of immunological memory
- live for a long time
- immunological memory of antibody needed against specific antigen
what is cell-mediated immunity?
T lymphocytes respond to cells of an organism that have been changed in some way
what is humoral immunity?
body responds to antigens found outside the cells
what is the process of cell mediated immunity?
1 - macrophages engulf and digest pathogens by phagocytosis and process the antigens to become antigen presenting cells
2 - receptors on some T helper cells fit the antigens
3 - the T helper cells become activated and produce interleukins, which stimulate more T cells to divide by mitosis
4 - the cloned T cells:
- develop into T memory cells
- produce interleukins that stimulate phagocytosis
- produce interleukins that stimulate B cells to divide
- stimulate development of a clone of T killer cells that are specific for the presented antigen
what is the process of humoral immunity?
1 - a B cell with the complementary antibodies will bind to the antigen on the pathogen
2 - the B cell engulfs and processes the antigen to become an APC
3 - activated T helper cells bind to B cell APC (clonal selection)
4 - interleukins produced by the activated T helper cells activate the B cells
5 - the activated B cell divides by mitosis to give clones of plasma cells and B memory cells (clonal expansion)
6 - cloned plasma cells produce antibodies that fit the antigens on the surface of the pathogen, bind to them or act as opsonins or agglutinins
7 - some cloned B cells develop into B memory cells
what is the primary immune response?
the relatively slow production of a small number of the correct antibodies the first time a pathogen is encountered
what is the secondary immune response?
the relatively fast production of very large quantities of the correct antibodies the second time a pathogen is encountered as a result of immunological memory
what is an autoimmune disease?
a condition or illness resulting from an autoimmune response
what is an autoimmune response?
response when the immune system acts against its own cells and destroys healthy tissue in the body
what is natural active immunity?
immunity which results from the response of the body to the invasion of a pathogen
what is natural passive immunity?
immunity given to an infant mammal by the mother through the placenta and the colostrum
what is artificial active immunity?
immunity which results from exposure to a safe form of a pathogen by vaccination
what is artificial passive immunity?
immunity which results from the administration of antibodies from another animal against a dangerous pathogen
what is a vaccine?
a safe form of an antigen, which is injected into the bloodstream to provide artificial active immunity against a pathogen bearing the antigen
what are the steps of vaccination?
1 - the pathogen is made safe so that the antigens are intact but there is no risk of infection
2 - small amounts of the safe antigen are injected into the blood
3 - the primary immune response is triggered by the foreign antigens and the body produces antibodies and memory cells
4 - if the live pathogen is encountered, the secondary immune response is triggered and the pathogen is destroyed
what can vaccines contain?
- killed or inactivated bacteria and viruses
- attenuated strains of live bacteria or viruses
- toxin molecules that have been altered or detoxified
- isolated antigens extracted from pathogen
- genetically engineered antigens
what is a pandemic?
when a communicable disease spreads rapidly across a number of countries and continents
what is an epidemic?
when a communicable disease spreads rapidly to a lot of people at a local or national level
what is Penicillin?
- first widely used, effective and safe antibiotic
- from the mould Penicillium chrysogenum
what are the sources of medicines?
- nature - bioactive compounds in plants, microorganisms
- designed using complex computer programmes to build three-dimensional models
- computers search through libraries of chemicals to isolate potentially useful action against pathogens
what is pharmacogenetics?
personalised medicine
combination of drugs that work with your individual combination of genetics and disease
what is selective toxicity?
the ability to interfere with the metabolism of a pathogen without affecting the cells of the host
what are antibiotic-resistant bacteria?
bacteria that have undergone mutation to become resistant to an antibiotic and then survive to increase in number
how can antibiotic-resistant infections can be reduced?
- minimising the use of antibiotics
- ensuring every course of antibiotics is completed to reduce risk of resistant individuals surviving and developing into a resistant strain population
- good hygiene in hospitals, care homes
