Module 4 - Communicable Diseases

What are pathogens and the four types?

communicable diseases are those that can be passed from one organims to another caused by microorganisms known as pathogens where organism pathogen lives called host and they live by taking nutrients from host but also causing damage in the process
by-product of pathogen life cycle is that they cause harm to their host which involves following stages travel from one host to another (transmission) - entering host’s tissues - reproducing - leaving host’s tissues
bacteria - produces toxins that damage body cells
viruses - use host cells to replicate before bursting out and destroying cells
protoctists (protists) - take over cells and break them open
fungi - digest living cells to destroy them some also produce toxins

What is bacteria?

belong to prokaryotae where cells are smaller than eukaryotic cells but can reproduce rapidly as quick as every 20 minutes so once in host body albe to multiple rapidly where their presence can cause disease by damaging cells or releasing waste products and or toxins that are toxic to the host and in plants lives in vascular tissue causing blackening and death of these tissues

What is fungi?

commonly fungus lives in skin of animal which form mycelium which grow under the skin and send out specialised reproductive hyphae which grows to skin to relases spores causing redness and irritation
in plants fungus lives in vascular tissue where it gains nutrients + hyphae release extracellular enzymes such as cellulases which causes decay and fruit and storage organs such as tubers will turn black and decay

What is a virus?

invade cells and take over genetic machinery and other organelles of the cell as they can cause cell to manufacture more copies of the virus then host cells eventually burst releasing many new viruses which will infect healthy cells

What are protoctista?

organisms usually cause harm by entering host cells and feeding on the contents as they grow eg malarial parasite feeds on haemoglobin inside red blood cells
some organisms can be difficult to classify where some organisms have many features that do not fit with other organims in previous groups

What is direct transmission?

pathogens transferred directly from one organism to another there is no intermediary and goes from host to new host
direct contact - skin-to-skin contact touching infected person,kissing or sexual intercourse eg HIV,bacterial meningitis,ring worm + athletes foot
risk reduced by better hygiene (washing hands regularly,keep surfaces clean,sterilising surgical instruments and condoms during intercourse)
airborne droplets - coughing or sneezing tiny droplets of mucus or saliva onto someone where pathogen carried in tiny water droplets in the air eg tuberculosis and influenza which can be reduced by covering mouth when coughing and using a tissues and ensure disposed of correctly
oral transmission - usually be eating food or drinking water contaminated with pathogen eg food poisoning and cholera prevented by treating wastewater and careful preparation
transmission by spores - carried in air or residue of surfaces/soil eg tentanus where diesease can be avoided by wearing face mask and washing skin after contras
transmission is passing a pathogen from an infected individual to uninfected individual

What is indirect transmission?

passed from one organism to another using an intermediate which could be:
food and drinking water - ingestion of contaminated food or water can cause disease
vectors - transmit pathogens from one host to another (eg mosquitos transmit malaria)
contaminated objects - pathogens from infected individuals can live on objects for a short time and infect others
an example vector is plasmodium parasite that causes malaria via entering human host via bite from a female mosquito
lifecycle:female mosquito sucks blood from person infected with malaria - plasmodium develops from gametes in infected blood and migrates to salivary glands of mosquito - mosquito bites an uninfected person - plasmodium from mosquito migrates into the person’s liver - then migrates into their blood - person now has malaria

What factors increase the risk of communicable disease?

living conditions - overcrowded areas increase risk of direct transmission
climate - for example warmer temperatures allow mosquitoes to breed and transmit malaria as many protoctists,bacteria and fungi can reproduce more rapidly in warm weather meaning global warming means tropical pathogens able to survive in Europe
social factors - eg lack of health education and healthcare systems increase the risk of communicable disease in poorer countries
weaker immune system eg a person with HIV

What is malaria and bacterial meningitis and more detail?

bacterium called which affects young children and teenagers as damages membranes of brain as becomes swollen which damages brain and spinal cord and can cause blood poisoning - transmitted by airborne droplets
protocist that affects humans and other mammals as damages red blood cells,liver and brain causing headaches and fevers as is a parasite in blood - transmitted by vectors (mosquitos) where vectors are an organism that carries a pathogen from one host to another

What is HIV/AIDS and influenza and more detail?

virus known as human immunodeficiency virus that affects human and non-human primates as gradually destroys the immune system as attacks cells compromising immune response - transmitted by exchange of bodily fluids
virus that affects mammals including humans as kills ciliated epithelial cells in gas exchange systems attacking respiratory system - transmitted by airborne droplets and contaminated objects

What is athlete’s foot and ring worm and more detail?

fungus which affects human as causes cracking and scaling of skin between toes - transmitted by contaminated objects
fungus that affects mammals including cattle and humans as causes spores to erupt through skin causing a circular red rash - transmitted by direct contact

What is tuberculosis and more detail?

bacterium which affects humans and pigs as damages the lungs and suppresses the immune system as kills cells and tissues - transmitted by airborn droplets
is not transmitted easily and often takes living in close proximity to people with disease for a long time before it is transmitted - BCG vaccination given to teenagers successfully reduce prevalence of TB in Western Europe however increase migration and more people living in overcrowded and poorly ventilated conditions meaning TB is rising in many Western cities

How are communicable diseases passed between plants?

can happen via direct transmission - involves direct contact of a healthy plant with any part of an infected plant where can enter the roots where once infected will infect all vascular tissue where pathogens in leaves are distributed when leaves shed and carry pathogen back to soil where it can grow and infect another plant + can also enter fruit and will be distributed in the seeds
also can happen via indirect transmission - can take place via soil contamination when infected plants leave pathogens or spores in the soil ready to infect other plants and also takes place using vectors

What are some examples of vectors in plant disease transmission?

wind - bacterial,viral or fungal spores are carried by the wind to uninfected plants
water - spores can travel on surface of water to reach uninfected plants
animals - insects and birds can carry pathogens or spores from one plant to another such as beetles which when attacks another plant pathogen is transmitted to uninfected plant eg fungus that causes Dutch elm disease carried by beetle
humans - pathogens and spores can be transmitted by handling plants,clothing,farming tools and practices

What factors increase the risk of communicable diseases in plants?

crop variety - some crops are more susceptible to disease than others
overcrowding - increases likelihood of direct contact
mineral nutrition - poor nutrition reduces resistance of plants
climate change - increased rainfall and wind increases the spread of disease

What is ring rot and tobacco mosiac virus and more detail?

rr - bacterium that affects potatoes and tomatoes as damages the leaves,tubers and fruit causing a ring of decay in vascular tissue of potato tuber
tmv - caused by virus that affects many plant species including tobacco and tomatoes as damages the leaves,tubers and fruit by molting and discolouration

What is black sigatoka and potato/tomato blight and more detail?

bs - fungus that affects banana plants as attacks and destroys the leaves,turning them black leaving spots reducing yield
p/t b - protoctist that affects potatoes and tomatoes as destoys leaves,tubers and fruit

How are plants used by pathogens?

plants make sugars in photosynthesis anc convert them into compounds like protein and oils therfore is a rich source of nutrients for many organisms such as all the pathogens,insects and vertebrates where the first might be pathogenic and the other two may act as vectors to help transmit these animals
plants don’t have immune system comparable with animals but have developed range of structral,chemical and protein-based defences which can defend invading organims and prevent them causing extensive damage which includes both passive defences to prevent entry and active defences which are induced when pathogen detected
passive defences are present before infection and their role is to prevent entry and spread of the pathogen which includes physical barriers and chemicals

What are some physical plant defences?

waxy cuticles - leave and stems covered in waxy cuticle which provides a physical barrier against pathogens as prevents water collecting on cell surfaces since pathogens collect in water and need it to survive so absence of water is passive defence
bark - most bark contains a variety of chemical defences that work against pathogenic organisms
cellulose cell walls - plant cells are surrounded by cells walls that form a physical barrier against pathogens + contain chemical defences that can be activated when pathogen detected
lignin thickening of cell walls - lignin is waterproof and almost completely indigestible
production of callose - when plants attacked by pathogens they produce a polysaccharide called callose which is deposited in sieve tubes around the sieve plates and blocks the flow in the sieve tube which can prevent a pathogen spreading around the plant
stomata closure - stomata are possible entry points for pathogens and when pathogenic organisms are detected the guard cells will close the stomata in that part of plant

What are the chemical defences?

plant tissues contain a variety of chemicals that have anti-pathogenic properties including terpenoids,phenols,alkaloids and hydrolytic enzymes where some of theses chemicals such as terpenes in tyloses and tannins in bark are present before infection however as production of chemicals requires a lot of energy so many chemicals are not produced until plant detects an infection

What are four production of chemical which act as chemical defences to plants?

insects repellents - reduce number of insect feeding on plants to prevent them from transmitting pathogens
insecticides - kill insects to prevent them from transmitting pathogen
antibacterial substances - chemicals such as antibiotics are produced to kill bacteria or inhibit their growth
toxins - some plants produce chemicals that break down into cyanide which is toxic when plant cells are attacked

What are active defences?

when pathogen attack specific chemicals in their cell walls can be detected by plant cells where these chemicals include specific proteins and glycolipids - plant responds by fortifying defences already present including increasing physical defences and producing defensive chemicals
cell walls become thickened and strenghthened with additional cellulose - deposistion of callose between plant cell wall and membrane near invading pathogen which impedes cellular penetration at infection site it strengthenes cell wall and blocks plasmodesmata - oxidative bursts that produce highly reactive oxygen molecules capable of damaging cells invading organims - increase in production of chemicals

What are terpenoids,phenols,defensins and hydrolytic enzymes?

t - range of essential oils that have antifungal and antibacterial properties + creates scent eg menthols by mint plants
p - also have same properties
d - small cysteine-rich proteins that have broad antimicrobial activity which appear to act upon molecules of plasma membrane of pathogens possibly inhibitng action of ion transport channels
h - found in spaces between cells including chitinases (break down chitin found in fungal cell walls) . glucanases (hydrolyses glycosidic bonds in glucans) and lysozymes (capable of degrading bacterial cell walls)

What are tannins,alkaloids,necrosis and tylose?

t - found in bark inhibit attack by insects which bind to salivary proteins and digestive enzymes such as trypsin deactivating enzymes where insects that ingest high amounts of this do not grow and die which helps prevent transmission of pathogens
a - nitrogen-containing compounds such as morphine give a bitter taste to inhibit herbivores feeding + if plant can reduce grazing by larger animals then it will suffer damage that can allow pathogens to enter the plant
n - deliberate cell suicide where few cells are sacrified by killing cells surrounding infection the plant can limit pathogens access to water and nutrients stopping it from spreading further around the plant which is bought about by intracellular enzymes that are activated by injury
t - balloon-like swelling that fills xylem vessels when tylose full formed vessel can no longer carry water blocking x vessel preventing pathogen spread which contains lots of chemicals such as terpines which are toxic

What are two groups defence mechanisms be split into and primary defences?

non-specific defences - act quickly to defend the body but responds in same way for all pathogens
specific defences - are slower to defend the body but produce a specific response for each pathogen + provide long-term immunity
primary defences are those that prevent pathogens entering the body and are non-specific as will prevent entry to any pathogen

What are some examples of non-specific barriers to prevent pathogen entry?

skin - mucous membranes - expulsive reflexes - blood clotting and wound repair - inflammation - phagocytosis

How can skin prevent the entry of pathogen?

acts as a physical barrier to block pathogens entering the body - also acts as chemical barrier by producing sebum an antimicrobial substances that lowers pH to inhibit pathogen growth
outermost layer epidermis consists of layer of cells where producec by mitosis at base then migrate out to surface of skin as they migrate they dry out and cytoplasm replaced by protein keratin called keratinisation and no longer alive when they reach surface + layer of dead cells is effective barrier

How can mucous membranes prevent the entry of pathogen?

parts of ears,nose,throat and digestive tract lined by mucous membranes as air and food taken in may contain microorganisms therefore at risk of infection so protected by mm which secrete mucus to trap pathogens and use lysosymes to destroy them - epithelial layer contains goblet cells which secrete mucus where in airway mucus lines passages and traps any pathogens that may be in air - epithelium also has ciliated cells which are hair-like organelles which move in coordinated way to waft layer of mucus along where move mucus up to top of trachea where it can enter oesophagus to be swallowed to digestive system where pathogens killed by acidity denaturies pathogens enzymes

How can expulsive reflexes prevent the entry of pathogen?

coughing and sneezing are methods for expelling foreign objects such as pathogens from gas exchange system in response to irritation where sudden expulsion of air will carry with it the microorganisms causing irritation - vomit and diarrhoea expel contents of gut along with any present pathogens

How can blood clotting and wound repair prevent the entry of pathogen?

cut to skin provides possible entry for pathogens and so blood clots act quickly to seal any wounds where clotting factor activates thrombokinase which with calcium ions able to convert protein Prothrombin into enzyme thrombin which catalyses conversion of soluble fibrinogen into insoluble fibrin - clot dries out to form a scab that blocks entry to body - after scab formed skin is capable of repairing itself to reform its physical barrier - epidermal cells underneath scab divide while damaged blood vessels regrow to provide oxygen and collagen fibres used to provide strength to new tissue under scab - once epidermis is required thickness scab breaks off and wound is healed

How can inflammation prevent the entry of pathogen?

sign tissue is infected is swelling,heat,redness and pain at site of infections or wounds - presence of microorganisms in tissue detected by mast cells which release chemicals (histamine) which has effects on surrounding tissue to help combat infection affecting blood vessels in two ways:blood vessels dilate which increases blood flow to area making it hotter preventing pathogens from reproducing + blood vessel walls become more permeable so they start to leak tissue fluid causing swelling and isolating any pathogens in damaged tissues - blood plasma + phagocytes leave blood and enter tissue fluid which leads to increased tissue fluid causing swelling which is drained into lymphatic system where lymphocytes are stored which can lead to pathogens being into contact lymphocytes intiating specific immune responses

What are some other primary defences?

eyes are protected by antibodies and enzymes in tear fluid (lysosomes) - ear canal lined by wax which traps pathogens - female reproductive system protected by mucus plug in cervix and by maintaining relatively acidic conditions

What are antigens?

unique molecules usually proteins that can be found on surface of cells where these antigens allow immune system to distinguish between body’s own cells (self) and foreign cells (non-self) where any foreign cells can be destroyed whilst leaving body’s own cells unaffected

What various cells can antigens identify?

pathogens - immune system recognises antigen as being foreign and activates cells to destroy the pathogen
abnormal body cells - cancerous or infected cells display abnormal antigens that trigger an immune response
toxins - are antigen molecules themselves and can be recognised by immune system
cells from other organisms of same species - cells may have different antigens to body’s own cells so are identified as being foreign so can cause rejection of transplanted organs

What are phagocytes and main two types?

type of white blood cell that engulf and destoy pathogens and found in blood and body tissues of many organisms - first line of secondary defence
neutrophils - rapidly engulf and destroy pathogens at site of infection - have multi-lobed nucleus and manufactured in bone marrow + often pushed out of blood into tissue fluid and released in large numbers in when infection occurs containing lots of lysosomes as engulf and digest pathogens - trap foreign matter in a large vacuole (phagosome) which fuses with lysosomes to digest matter
macrophages - these engulf and digest pathogens but also present pathogens antigens on its cell surface to activate other cells in immune system - larger cells manufactured in bone marrow and found in lymph nodes where they mature into

What is the role of macrophages?

play important role in initiating the specific responses to invading pathogens as when m engulfs a pathogen it does not fully digest it - the antigen from surface of pathogen is saved and moved to special protein complex on surface of the cell becoming an antigen-presenting cell which exposes the antigen on its surface so other cells of the immune system can recognise the antigen where the special protein complex ensures antigen-presenting cells not mistaken for a foreign cell and attacked by other phagocytes

What are the steps of phagocytosis?

pathogen releases chemicals that attract phagocyte - phagocyte recognises the pathogen’s antigens as non-self which causes phagocyte to bind to the pathogen - phagocyte engulfs the pathogen - pathogen is now contained within vesicle known as phagosome - lysosome containing hydrolytic enzymes called lysozymes which fuses with phagosome to form a phagolysosome - lysozymes digest and destroys pathogen - phagocyte presents pathogens antigen on its surface to activate other cells in immune system phagocyte then referred as an antigen-presenting cell

How are phagocytes specialised to attack specific pathogenic cells?

receptors on plasma membrane that can bind to opsonin or specific antigen - a lobed nucleus that allows cell to squeeze through small gaps - well-developed cytoskeleton which helps cell to change shape to engulf the pathogen and to move lysosomes and vacuoles around cell - many lysosomes contain lysin and lytic enzymes - many mitochondria to release energy from glucose - a lot of ribosomes to synthesise enzymes involved

What are secondary defences?

used to combat pathogens that have entered body where when a pathogen invades the body it is recognised as foreign by chemical markers on its outer membranes called antigens which are proteins or glycoproteins intrinsic to plasma membrane where antigens are specific to the organism where our own cells have antigens but these are recognised as our own and don’t produce a response

What are two molecules that help with phagocytosis?

cytokines are chemicals released by phagocytes that have engulfed a pathogen and act as cell-signalling molecules to trigger the movement of other phagocytes to site of infection + also trigger an increase in body temperature which inhibits reproduction of pathogens and allows specific immune system to work faster
opsonins are chemicals that bind to pathogen by attaching to antigens on its surface to make them easily recognisable where phagocytes contain receptors on their cell-surface which bind to common opsonins making it easier for phagocyte to bind to pathogen and destroy it therefore enhancing - some not very specific so can attach to variety of pathogenic cells where role to enhance ability of phagocytic cells to bind and engulf pathogens

What are antigen presenting cells,cytokines and opsonins?

a cell that isolates the antigen from a pathogen and places it on the plasma membrane so that it can be recognised by other cells in the immune system
hormone-like molecules used in cell signalling to stimulate immune response
proteins that bind to the antigen on a pathogen and then allow phagocytes to bind

How does the specific immune response differ?

depends on type of lymphocyte produced in bone marrow where the two types are:
T lymphocytes - T cells mature in thymus gland and involved in cellular response where they respond to antigens presented on body cells
B lymphocytes - B cells mature in the bone marrow and involved in humoral response where they produce antibodies found in body fluids
both have large nucleus and specalised receptors on plasma membrane which eventually produces antibodies which neutralise foreign antigens and also provides long-term protection from disease as produces immunological memory through memory cell release which circulate body for years
where antigen-presenting cell moves around body where it comes in contact with either if these cells that activate full immune response where may only be one cell with correct recognition site for the antigen so job to increase chances antigens will come in contact with them

What are the four types of T cells?

T helper cells - T killer cells - T regulator cells - T memory cells

What are T helper cells?

have receptors on cell-surface that bind to complementary antigens on antigen-presenting cells and produce interleukons (type of cytokine) which stimulates immune response of B cells or phagocytes and can also form memory cells or T killer cells

What are T killer cells?

these cells kill abnormal and foreign cells by attacking infected body cells by producing a protein known as perforin and this proteins makes holes in cell-surface membrane causing it to become freely permeable and causing cell death

What are T regulator and memory cells?

these cells supress immune system after pathogens have been destroyed and this helps to prevent immune system from mistakenly attacking body cells
these cells provide long-term immunity against specific pathogens and they provided a rapid response if body is reinfected by same pathogen by remaining in the blood

What is the specific immune response?

activation of specific B and T cells called clonal selection (selection of specific B or T cells that is specific to antigen) which causes series of events that lead to production of antibodies that can produce the specific pathogens and memory cells that will provide long-term immunity where whole series of events is stimulated and coordinated by a number of hormone-like chemicals called cytokines which stimulate differentiation and activity of macrophages,B cells and T cells

What are the stages of the cellular response?

macrophage engulf pathogens which have specific antigens and display their antigens on cell-surface and now known as antigen-presenting cells
T and B lymphocytes with complementary receptors on plasma membrane bind to these antigens known as clonal selection where can be achieved directly when pathogenic cells enter lymph nodes or via action of antigen-presenting cells
on binding after correct lymphocyte activated the T helper cell is activated to divide by mitosis to form genetically identical clone as must increase in numbers to become effective known as clonal expansion
then differentaition occurs as clones of the lymphocytes develop into a range of useful cells

What different functions can cloned T cells carry out?

develop into T memory cells - these circulate in body to provide long-term immunity
develop into T killer cells - these destroy infected cells that display foreign antigen
develop into T regulator cells - these shut down immune system after pathogen removed + involved in preventing autoimmunity
stimulate phagocytosis done by T helper cells - cells produce interleukins which stimulate phagocytes to engulf pathogens
stimulate division of B cells done by T helper cells - cells produce interleukins which stimulate B cells to divide and produce antibodies

What is cell signalling?

needed for coordinated action of a range of cells which need to communicate which is achieved through the release of hormone-like chemicals called cytokines where in order to detect a signal target cell must have cell surface receptor of complementary shape to shape signalling molecule
examples of communication using cytokines:
macrophages release monokines where some attract neutrophils and others stimulate B cells to differentiate and release antibodies
T cells and macrophages releases interleukins which are signalling molecules used to communicate between different wbc these can stimulate clonal expansion and differentiation of B and T cells

What is the structure of antibodies?

y-shaped glycoproteins made up of four polypeptide chains,two heavy chains and two light chains where polypeptide chains are held together via disulphide bridges
made of various regions:constant region which is the same for all antibodies and binds to receptors on cells such as B cells
variable region - different for each antibody as its shape is complementary to specific antigen and this part of antibody that binds to antigens
hinge region - allows antibody to be flexible so it can bind to multiple antigens at once

What are the functions of antibodies?

main function is to bind to specific antigens on pathogens surface where each antibody has unique binding site that fits onto specific antigen forming antigen-antibody complex
3 roles to help destroy pathogens: agglutination of pathogens which involves clumping pathogens together to enable easier phagocytosis
neutralisation of toxins which is when antibodies bind to toxins to inactivate them
preventing pathogens from binding where antibodies bind to pathogens to stop them from infecting body cells

What is agglutination of pathogens?

antibodies act as agglutins causing pathogen to clump together which makes it easier for phagocyte to locate pathogens and allows them to engulf number of pathogens at once
antibodies also act as opsonins making pathogens easily recognisable by phagocytes

What is neutralisation of toxins?

antibodies act as antitoxins where they bind to toxins produced by pathogens and this binding neutralises toxins to prevent them from damaging body cells

How do antibodies prevent pathogens from binding to cells?

when antibodies bind to pathogens antigens they block cell-surface receptors needed to bind to host cells which means pathogens cannot bind to or invade host cells