Communicable diseases Flashcards
Pathogens
-organisms that cause disease are called pathogens
-the organism in which they live is called the host
-a host body creates a good habitat in which microorganism live
-as result there are numerous types of microorganisms that live in or on the body of another organism
-pathogens live by taking nutrition from their host but also cause damage in the process - can be considerable
Bacteria
-belong to the kingdom prokaryote
-their cells are smaller than eukaryotic cells but can reproduce rapidly- in right conditions, every 20 minutes
-once in host body, they can multiply rapidly
-their presence can cause disease by damaging cells or by releasing waste products/ and or toxins that are toxic to the host
-in plants bacteria often live in the vascular tissues and cause blackening and death of these tissues
Fungi
-fungi can cause variety of diseases in plants and animals
-there are common fungal infections where the fungus lives in the skin of an animal and where its hyphae which form a mycelium grow under the skins surface
-fungus can send out specialised reproductive hyphae which grow to surface of skin to release spores which cause redness and irritation
-in plants the fungus often lives in vascular tissue where it can gain nutrients
-the hyphae release extracellular enzymes such as cellulases to digest the surrounding tissues which causes decay
-leaves will often become mottled in colour, curl up and shrivel before dying
-fruit and storage organs such as tubers (potatoes) will turn black and decay
Viruses
-viruses invade cells and take over the genetic machinery and other organelles of the cell
-they then cause the cell to manufacture more copies of virus
-they then cause the cell to manufacture of copies of virus
-the host cell eventually bursts releasing many new viruses which will infect healthy cells
Protista
-these organisms usually cause harm by entering host cells and feeding on contents as they grow
-malarial parasite Plasmodium has immature forms that feed on haemoglobin inside red blood cells
Examples of bacteria
-tuberculosis - Myobacterium tuberculosis - disease affects many parts of body, killing cells and tissues, the lungs are often most affected
-bacterial meningitis - Neisseria meningitis - infection of mengines (membranes surrounding brain and spinal cord) cause swollen and damage to brain and nerves
-ring rot - Clavibacter - ring of decay in vascular tissue of potato tuber or tomato, accompanied by leaf wilting
-divide by binary fission
-treated by antibiotics - penicillin, ampicillin- issue of resistance
Examples of fungi
-ringworm - growth of fungus in skin with spores erupting through skin to cause a rash
-athletes foot - Trichophyran rubrum- growth under skin of foot-particularly between toes
-black sigatoka- Mycosphaerella - causes leaf sports on bananas plants reducing yield
Examples of proctist
-blight- phytophthora - affect tomato leaves and potato tubers
-malaria- Plasmodium- parasite in blood that causes headache and fever and may progress to coma and death
Examples of viruses
-tobacco mosaic virus- causes mottling and discolouration of leaves
-influenza- from family Orthomyxoviridae - attacks respiratory system and causes muscle pains and headaches
-HIV/AIDS - attacks cells in immune system and comprises the immune response
How do viruses cause disease
-virus attaches to cell
-virus DNA injected into cell
-viral components assembled
-viruses release, death of cell
-no antibiotics for viruses
-anti virals e.g. inhibitor to protease or inhibitor to reverse transcriptase
FACTORS OF TRANSMISSION: direct physical contact
-such as touching a person who is infected or touching contaminated surfaces that harbour the pathogens
-for example HIV, bacterial meningitis, ringworm, athletes foot
-hygiene: washing hands regularly- especially after using toilet
-keeping surfaces clean: especially door handles
-cleaning and disinfecting cuts and abrasions
-sterilising surgical instruments
-using condoms during sexual intercourse
FACTORS AFFECTING TRANSMISSION: faecal oral transmission
-usually by eating food or drinking water contaminated by the pathogen
-for example, cholera, food poisoning
-using human sewage to fertilise crops is common practise in some parts of world
-treatment of waste water and treatment of drinking water are important ways to reduce waste
-thorough washing of all fresh food
-careful preparation and thorough cooking of all food
FACTORS AFFECTING TRANSMISSION: droplet infection
-pathogen is carried in tiny water droplets in air
-for example tuberculosis, influenza
-catch it, bin it, kill it
-cover your mouth when coughing or sneezing
-use a tissue and dispose of it correctly
FACTORS AFFECTING TRANSMISSION: spores
-transmission by spores which are resistant stage of pathogen
-these can be carried in air or residue on surfaces/ in soil
-for example tetanus, anthrax
-use a mask
-washing skin after contact with soil
Social factors that affect transmission
-overcrowding, many people living and sleeping together in one home
-poor ventilation, droplets passed around
-poor diet
-homelessness, weaker immune system
-poor health, especially if person has HIV/AIDS as they are ore likely to contract other diseases
-living or working with people who have migrated from areas where a disease is more common
Indirect transmission
-some pathogens transmitted indirectly via a vector
-a vector is another organism that may be used by pathogen to gain entry to primary host
-for example Plasmodium parasite that causes malaria enters human host via bite from female Anopheles mosquito
Direct transmission of plant pathogens
-many pathogens present in soil and will infect plants by entering roots- especially if these have been damaged as a result of replanting, burrowing animals or movement caused by a storm
-many fungi produce spores as a mean of asexual/sexual reproduction- may carried by wind therefore airborne
-once pathogen is inside plant it may infect all vascular tissue
-pathogens in leaves are distributed when leaves are shed and carry the pathogens back to soil where it can grow and infect another plant
-pathogens can also enter fruit and seeds and then be distributed with the seeds so that many or all of the offspring are infected
Indirect transmission of plant pathogens
-often occurs as a result of insect attack
-spores or bacteria become attached to a burrowing insect such as a beetle which attacks and infected plant
-when that beetle attacks another plant, the pathogen is transmitted to the uninfected plant
-the beetle is acting as a vector
-for example the fungus that causes the Dutch elm disease is carried by beetle
-also ashdieback disease
How do diseases change with the climate
-many protoctists, bacteria and fungi can grow and reproduce more rapidly in warm and moist conditions
-therefore they tend to be more common in warmer climates
-in cooler climates these pathogens may be damaged or even killed by cold winter weather- such winter weather will certainly reduce their ability to grow and reproduce
-as result, there is greater variety of diseases to be found in warmer climates and animals, plants living in these regions are more likely to be infected
List some passive, physical plant defences
-cellulose cell wall=not only acts as a physical barrier but most contain chemical defences that can be activated when pathogen detected
-lignin thickening= lignin is waterproof and almost completely indigestible
-waxy cuticle=prevent water collecting on cell surfaces, prevents survival of pathogens
-bark=contains variety chemical defences against pathogens
-stomatal closure= stomata possible points of entry for pathogens, closure is controlled by guard cells. When pathogen detected, guard cells close stomata
-callose=large polysaccharide that deposited in sieve plates and blocks flow in sieve tube (prevents pathogen spreading around plants)
-tylose formation= balloon like swelling or projection that fills xylem vessel. When fully formed it plugs vessel and can no longer carry water. Prevents spread of pathogens and has a high concentration of chemicals such as terpenes that are toxic to pathogens
Chemical defences of plants
-plant tissues contain variety of chemicals that have antipathogenic properties- include terpenoids, phenols, alkaloids and hydrolytic enzymes
-some of these chemicals such as terpenes and tannins are present before infection
-however production chemicals requires a lot of energy and therefore many chemicals not produced until plant detects infection
What are active plant defences
-when pathogens attacks, specific chemicals in their cell walls can be detected by the plant cells
-these chemicals include specific proteins and glycolipids
-plant responds by fortifying the defences already present:
-cell walls become thickened and strengthened with additional cellulose
-deposition of callose between plant cell wall and cell membrane near invading pathogen- impeded cellulose penetration at site of infection, strengthening cell wall and impeding plasmodesmata
-oxidative bursts that produce highly reactive oxygen molecules capable of damaging cells of invading pathogens
-increase in production of chemicals
ACTIVE DEFENCE: terpenoids
-volatile organic compound common in conifers
-a range of essential oils that have antibacterial and antifungal properties
-may also create scent for example menthols and menthones produced by mint plants
ACTIVE DEFENCE: phenols
-these also antibiotic and antifungal properties
-tannins found in bark inhibit attack by insects
-these compounds bind to salivary proteins and digest enzymes such as trypsin, deactivating the enzymes
-insects that ingest high amounts of tannins do not grow and eventually die
-helps to prevent transmission of pathogens
-usually in berries, red wine
ACTIVE DEFENCES: alkaloids
-nitrogen containing compounds such as caffeine, nicotine, cocaine, morphine, solanine
-these give a bitter taste to inhibit herbivores feeding
-they also act on a variety metabolic reactions via inhibiting or activating enzyme action
-some alkaloid inhibit protein synthesis
-if plant can reduce grazing by larger animals then it will suffer less damage that can allow pathogens to enter the plant
ACTIVE DEFENCES: defensins
-small cysteine rich proteins that have broad anti microbial activity
-they appear to act upon molecules in plasma membrane of pathogens, possibly inhibiting action of ion transport channels
ACTIVE DEFENCES: hydrolytic enzymes
-found in spaces between cells
-include chitinases (break down chitin found in fungal cell wall), glucanases (hydrolyse glycosidic bonds in glucans), lysozymes (capable of degrading bacterial cell wall)
What is necrosis
-deliberate cell suicide
-a few cells sacrificed to save rest of plant
-by killing cells surrounding infection the plant can limit pathogens access to water and nutrients and can therefore stop spreading further across the plant
-necrosis is brought about by intracellular enzymes that are activated by injury
-these enzymes destroy damaged cells and produce brown sports on leaves or die back
What is canker
–sunken necrotic lesion in woody tissue such as main stem or branch
-cause death of the cambium tissue in the bark
PRIMARY DEFENCE: the skin
-the body is covered by skin- this is main primary defence
-the outer layer of skin is called epidermis and consists of layers of cells- most called kerotinocytes (born basal layer)
-these cells are produced by mitosis at base of epidermis
-they then migrate to surface of skin- as they migrate they dry out and cytoplasm is replaced by protein keratin- insoluble, penetrable to bacteria and viruses
-this process is called keratinisation and it takes about 30 days
-by the time the cells reach the surface they are not alive
-the keratinised layer of dead cells acts as an effective barrier to pathogens- eventually dead cells slough off
