Module 4.1 - Communicable Diseases Flashcards
What is a pathogen and how do they live?
- an organism that causes disease
- live on or in a host organism
- take nutrients from the host ( causes damage )
Explain bacteria
- prokaryote kingdom
- reproduce rapidly
- damage cells/ release waste or toxins ( e.g in plants, live in vascular tissue and cause it to die )
Explain fungi
- can live in skin of animals and where its hyphae which form a myecilium, grow under skin. Sends out special reproductive hyphae which release spores- causes irritation and redness
- can live in vascular tissue in plants to gain nutrients, hyphae release extra cellular enzymes (e.g cellulases) to digest surrounding tissue causing decay and death. Fruit and storage organs turn black and decay, leaves become mottled in colour, shriven and curl up.
Explain viruses
- Invade cells, take over genetic machinery and organelles
- cause cell to make copies of virus
- host cell bursts releasing more viruses which infect healthy cells
Explain proctoctista
Usually enter host cells and feed in contents and grow
-e.g plasmodium ( causes malaria) has forms that feed on haemoglobin in red blood cells
What causes tuberculosis and what are its characteristics?
- bacteria: mycobacterium tuberculosis and M. Bovis
- kills cells and tissues in the body, affects the lungs the most
What causes bacterial meningitis and what are its characteristics?
- bacteria: neisseria menigitidis or streptococcus pneumonia
- infection of meninges - membranes that surround brain and spinal cord, become swollen and damage brain and nerves
What causes ring rot and what are its characteristics?
-Bacterium: clavibacter michiganesis subsp. sepedonicus
What causes HIV/ AIDS and what are its characteristics?
Virus: human immunodeficiency virus
-attacks cells in immune system and compromises immune response
What causes influenza and what are its characteristics?
- Virus: from family orthomyxoviridae
- attacks respiratory system, causes muscle pain and headaches
What causes tobacco mosaic virus and what are its characteristics?
- Virus: tobacco mosaic virus
- causes mottling and discolouration of leaves
What causes black Sigatoka and what are its characteristics?
- fungus : mycospharella fijiensis
- causes leaf spots on banana plants, reducing yield
What causes blight (tomatoes and potatoes) and whT are its characteristics?
- proctoctistan: phytophthora infestans
- affects leaves and potato tubers
What causes ringworm ( cattle ) and what are its characteristics?
- fungus: trichophyton verrucosum
- fungus growth in skin with spores causes erupting through skin, causes a rash
What causes athletes foot and what are its characteristics?
Fungus: trichophyton rubrum
-growth under skin of feet, between toes
What causes malaria and what are its characteristics?
Proctoctistan: plasmodium vivax
- carried by a vector: female Anopheles mosquito
- causes headache and fever which can cause a coma and death
What is the life cycle of a pathogen?
- travel from one host to another (transmission)
- enter a hosts tissue
- reproduce
- leave the hosts tissue
Describe the 4 main means of transmission
-direct physical contact
touching infected person or contaminated surface ( e.g HIV, bacterial meningitis, ringworm, athletes foot ). Affected by hygiene- wash hands, clean surfaces, clean cuts, sterilise surgical instruments, use condoms.
-faecal-oral transmission
eating or drinking contaminated things ( e.g cholera, food poisoning ). Treat waste and drinking water to reduce risk, wash dress food with clean water, carefully prepare food.
-droplet infection
pathogen carried by water droplets in air ( e.g tuberculosis, influenza )
Catch it, bin it, kill it. Cover mouth when coughing or sneezing, use tissue and dispose
-spores,
resistant stage of pathogen, carried in air or on soil surfaces ( anthrax, tetanus) use masks and wash skin after soil contact
What social factors affect transmission?
- overcrowding
- poor ventilation
- poor health e.g HIV/aids
- poor diet
- homelessness
- living or working with people who have migrated from areas where the disease is more common
What is direct transmission?
Pathogen passes from host to host
What is indirect transmission?
Pathogen passed from host to host via a vector
What is transmission
Passions a pathogen from an infected host to an uninflected individual
Explain the transmission of plant pathogens
- direct and indirect
- some in soil, taken up by roots ( esp if damages by replanting, burrowing animals or storm)
- fungi produce spores ( sexual or asexual ) carried by wind = airborne transmission
- infects vascular tissue, when leaves shed, pathogen in leaves carried to soil and can infect another plant
- enter fruit and seeds, distributed with seeds, infecting offspring
- indirect - insect attack, spores or bacteria attach to burrowing insect, when it attacks another plant, it transmits the pathogen. E.g beetle, the insect acts as a vector
How does climate affect disease?
- pathogens grow and reproduce more rapid when warm and moist so more common in these climates
- cold climates damage or kill pathogens or reduce ability to grow and reproduce.
- greater variety of diseases in warmer climates
(MA -ext) Why are the rates if HIV/AIDS higher in sub-Saharan Africa than in the rest of the world?
- poverty
- less education about means of transmission
- could be more promiscuity/more working in sex industry
- lower availability of condoms
- religious reasons for not wearing condoms
- many countries have promoted denial of existence
- fewer medical facilities for screening etc
- less screening of blood for transfusions etc
- more infected mothers have to breast feed - no alternative
- more cases of rape
- more intravenous drug abuse
- more use of shared needles
(MA -ext) Why hasn’t TB been eradicated?
- LEDCs can’t afford vaccines/antibiotics
- vaccine isn’t 100% effective
- bacteria have become antibiotic resistant
- people don’t finish long course of antibiotics
- lack of education about TB
- people still drink unpasteurized milk (LEDCs)
- migration of carriers (no symptoms)
(MA) Describe phagocytosis (non-specific immune response).
- phagocytes: engulf and digest pathogen
- receptor on phagocyte’s cell surface membrane binds to antigen on pathogen’s cell surface membrane
- pathogen engulfed by endocytosis
- this produces a phagosome (phagocytic vesicle)
- lysosomes fuse with phagosome, releasing enzymes (lysins) into it
- the pathogen is digested into amino acids and fatty acids etc
- products are absorbed into cytoplasm by diffusion
(MA) What are the roles of antibodies?
-bind to antigens on pathogen
-neutralization of pathogens
> antibodies cover binding site of pathogen
> which prevents their entry to host cell
-agglutination of pathogens
> multiple variable regions allow antibodies to clump/bind together many pathogens
> clump too large to enter host cell and increases likelihood of being consumed by (named) phagocyte
(MA) Describe the immune response of T lymphocytes (cellular response).
- macrophages engulf + digest pathogens incorporating pathogen’s antigens into their own cell surface membrane; now antigen presenting cell
- this helps select the right specific T lymphocytes with receptors complementary in shape to antigens; clonal selection
- once the correct T lymphocytes are selected, they divide by mitosis in clonal expansion
- T helper cells release cytokines with specific shapes which bind to complementary receptors on the cell surface membrane in B lymphocytes, stimulating them, to divide by mitosis and differentiate. They also stimulate macrophages to carry out more phagocytosis
- T killer cells kill infected host cells by secreting protease enzyme into them
- T memory cells stay in the blood in case there’s a secondary infection by the same pathogen. They allow a faster secondary response as they recognize the antigen + can make clones + differentiate to form new T cells more quickly than in the primary response
(MA) Explain examples of cell signaling in the immune response.
- pathogen’s antigens communicate to body cells that they are foreign
- infected with foreign antigens on surface communicate to lymphocytes to be selected in clonal selection + to T killer cells that they need to be killed
- macrophages engulf + digest pathogens + incorporate the pathogen’s antigens on their cell surface membrane; communicates to T lymphocytes to be selected in clonal selection
- T helper cells release cytokines; bind to receptors on B cells + stimulate them to divide by mitosis and differentiate
(MA) Describe the changes and roles of B lymphocytes in an immune response.
- humoral response
- specific B lymphocytes w/ receptors complementary in shape to antigens on invading pathogen’s surface are selected: clonal selection
- cytokines released by T helper cells stimulate B lymphocytes to divide by mitosis: clonal expansion, then differentiate into plasma cells + B memory cells
- plasma cells produce and secrete antibodies complementary in shape to the antigen, causing agglutination or neutralisation of pathogens
- B memory cell stay in blood in case there’s a secondary infection by the same pathogen. Allow faster secondary response as they recognise antigen + can make clones to form new plasma cells so antibodies are made more quickly than in the primary response
(MA) What examples of cell signalling can be seen in the immune response?
- pathogen’s antigens communicate to body cells they’re foreign
- infected cells w/ foreign antigens on surface communicate to lymphocytes to be selected in clonal selection + to T killer cells that they need to be killed
- macrophages engulf + digest pathogens + incorporate pathogen’s antigens into cell surface membrane. Communicates to T lymphocytes to be selected in clonal selection
- T helper cells release cytokines: bind to receptors on B cells + stimulate them to divide by mitosis + differentiate
(MA) Describe the difference in speed between the primary and secondary immune response against a pathogen.
First infection + primary response
-time delay to trigger immune response after first infection
-no B memory cells so slow antibody production + few produced
Secondary infection/response
-shorter delay before response. Reponse is much quicker
-B memory cells specific to the antigen of pathogen have remained in blood after being produced in primary response. Can clone + differentiate to make plasma cells to make more antibodies much more quickly. Give immunity to a disease
What’s the main difference between animal and plant pathogen response?
Plants don’t have an immune system
What are the passive plant defences?
- cellulose cell wall- physical barrier and chemical
- lignin thickening of cell walls- waterproof and indigestible
- waxy cuticle-prevents water collecting, pathogens collect in water and need it to survive
- bark- chemical and physical
- stomata closure- entry point for pathogens, controlled by guard cells, close stomata when pathogens detected
- callose- deposited in sieve plates, blocks flow in sieve tube, prevents pathogen spread
- tylose- balloon like swelling fills xylem, plugs vessel so xylem can’t carry water. High terpenes ( chemicals ) that are toxic to pathogens
-chemical- ( e.g terpenoids, phenols,alkaloids, hydrolytic enzymes)
(MA) Which groups of people should be immunised and why?
- elderly/young children: weak immune systems/young children have had little time to build up natural immunity to many diseases
- HIV/AIDS sufferers: weak immune systems so can’t produce many antibodies themselves
- pregnant women: foetus has undeveloped immune system
- health workers: more likely to be at risk of getting disease
- those with chronic diseases like TB/autoimmune disease: already in poor health + bodies may be unable to withstand further disease
(MA) Why do some people choose not to get immunised?
- too busy/can’t be bothered to go to the doctors
- media scare stories
- concerned about side effects
- allergic to vaccine
- fear of needles
- religious reasons
- cost of vaccine is too expensive
(MA) Why, other than the direct health benefits, does the government want people to be vaccinated?
- prevention of disease can save days lost at work by many people, prevents harm to the economy
- costs less to immunise people than to treat them
- health service may not be able to cope if large numbers of people became infected
(MA) Why are the elderly (and others) encouraged to get a vaccine for the influenza virus every year?
- vaccine is changed evert year
- different strains of virus each year as it has mutated from previous year
- new strains have different antigens
- old antibodies from previous year aren’t complementary to new antigen + new vaccination will encourage new antibodies to be made
(MA) How do governments go about vaccinating people to control disease?
-herd vaccination > vaccinate all people at risk > stops infection spreading -ring vaccination > requires people to report victims > vaccinate all people living with or near victim > contains spread within ring
(MA) Why has it not been possible to produce an effective vaccine for malaria?
- different strains of the protoctist each year as it has mutated from previous year
- new strains have different antigens
- more than one stage in its life cycle + different stages have different antigens + would require different vaccines
- Plasmodium concealed in liver cells + RBCs so only exposed to immune system for a short period of time
(MA) Describe the life cycle of malaria.
- person w malaria has gametes of P. vivax in blood
- person bitten w female Anopheles mosquito + gametes in blood go into its stomach
- gametes fuse + zygotes of P. vivax develop in stomach
- develop into infective stages + migrate to salivary glands of mosquito
- mosquito bites uninfected person + injects in some of its saliva containing infective P. vivax
- infective stages of P. vivax enter new host’s liver + divide (by mitosis)
- enter blood to feed on Hb in RBCs + make more gametes in process
(MA) Describe the effects on the body of HIV (human immunodeficiency virus).
- causes AIDS (acquired immune deficiency disease)
- HIV positive = inactive version of virus present (no symptoms of AIDS), can go unknown for a long time (during which time it can be transmitted)
- active version of virus destroys T helper cells
- lowers ability to destroy pathogens
- increased likelihood of contracting (AIDS related) diseases e.g. pneumonia
(MA) What is TB and how is it transmitted?
- bacteria: Mycobacterium tuberculosis + M. bovis
- transmitted by droplet infection (e.g. droplets from coughs/sneezes being inhaled)
- TB usually found in lungs
- can also be transmitted through milk/meat of infected cattle
(MA) What factors are likely to increase the transmission of pathogens e.g. TB?
- overcrowded living conditions
- poor ventilation
- poor health (or impaired immune system)
- poor diet
- homelessness
- living or working w people who have migrated from areas w high prevalence of TB
