Disease Flashcards
what are communicable disease caused by
pathogens
what is a communicable disease
a disease that can be passed from organism to another
what are vectors
things can carry pathogens from one organism to another
what are the 2 main ways that bacteria can be classified
by their basic shapes
by their cell walls
what are the different shapes of bacteria
rod shaped
spherical
comma shaped
spiralled
corkscrew
what are the 2 different main types of bacterial cell walls and how do they look under a microscope when stained
gram positive (blue-purple under a microscope when stained
gram negative (red under a microscope when stained)
what are the size of viruses
0.02-0.3 micrometers in diameter
what is the basic structure of a virus
genetic material (dna or rna) surrounded by protein
how do viruses work
takes over cellular metabolism.
viral genetic material is inserted into the genetic material of the host cell.
the host cell then makes more viruses which then burst out of the cell destroying it.
what are bacteriophages
viruses that attack bacteria
they take over bacterial cells and use them to replicate, destroying the bacteria at the same time
what kind of celled organisms are protists
eukaryotes
what kind of celled organisms are bacteria
prokaryotes
they do not have a membrane bound nucleus nor organelles
are viruses prokaryotes or eukaryotes
neither because they are not living
how do protists work
they take over a cell, digest the insides and use this as a medium to reproduce, before bursting out.
how do fungi work
digest and destroy living cells
why can fungi spread rapidly
when they reproduce they produce millions of tiny spores which can spread over long distances
which pathogens damage the host tissues directly
viruses
fungi
protists
which pathogens produce toxins which damage host tissues
bacteria
fungi
how does secreted bacterial toxins damage tissues
secreted toxins damages the cells of the host organism by breaking down the plasma membrane or inactivating enzymes and some interfere with genetic material so the cell cannot divide
what is ring rot and how is it spread
a bacterial disease of potatoes, tomatoes and aubergines
caused by bacterium spread by direct contact, or indirect contact, via infected water, machinery etc.
creates ring shaped damage to vascular tissue in plants including potatoes and tomatoes
there are some resistant strains
good hygiene practice and quarantine to avoid spread
what is tmv and how is it spread
a virus that affects tomatoes, tobacco and peppers
spread by direct contact, including human handling. it also persists in dead plant matter
causes leaf discolouration that leads to stunted growth and reduced yields
minimise spread by sanitation (remove affected material, washing hands) and crop rotation
what is potato blight and how is it spread
a protist that acts like a fungus that affects species including as potatoes and tomatoes
spread by wind-borne pores
hyphae penetrates and kills cells in leaves / tubers / fruits massively affecting yields
no cure - careful management and chemical treatment reduces spread and impacts
resistant strains exist
what is black sigatoka and how is it spread
a fungus that affects banana plants - hyphae penetrate leaves, killing cells and turning leaves black
spread by wind and water borne spores
significantly reduces yields
good husbandry to reduce effects - rotation, intercropping, good drainage, remove leaves with infection
application of fungicides
GM species
what is TB and how does it spread
a bacteria that is
caused by the airborne bacteria mycobacterium tuberculosis
it is a widespread disease that affects the respiratory system
it can be treated with antibiotics but resistant strains of TB have emerged
what is HIV/AIDS and how does it spread
caused by retrovirus that affects and kills t-helper cells, compromising the immune system and leading to secondary infections such as pneumonia, TB and some forms of cancer
spread by the exchange of bodily fluid
anti-retroviral drugs slow the progress of disease
no current cure due to lifecycle of virus and mutation rate
what is influenza and how is it spread
a virus that is spread by droplet infection and direct contact
affects and kills ciliated epithelial cells in gas exchange system leading to fever, aching, headaches. can cause death (often from secondary respiratory system)
short term vaccines produced but rapid mutation rates means that the production of a complete vaccine is not possible
what is malaria and how is it spread
caused by a protist
life cycle:
a person with malaria → gametes of plasmodium in blood → female mosquito sucks blood → plasmodium develops and migrates to a mosquito’s salivary gland → an uninfected person is bitten → plasmodium migrates to liver → plasmodium migrates to blood
malaria is transported via the vector of a mosquito
treated with anti malarial drugs - they are mixed together due to resistance
what is ring worm and how is it spread
a fungus that affects many mammals - causing unsightly, itchy, round areas of skin that can cause further infection
spread by direct contact
treated with fungicidal creams
what is athlete’s foot and how is it spread
a fungus that digests skin between toes - causing cracking and scaling
spreads through direct contact with spores
treated with fungicidal creams
how are pathogens identified
traditionally, pathogens were identified using a microscope
monoclonal antibodies
DNA sequencing
how does TB work
when a person becomes infected with TB, an immune response is triggered
in healthy people, white blood cells called macrophages engulf the bacteria by phagocytosis, controlling the infection
a tissue mass called a tubercle forms around the infected site, and after 3-8 weeks, the infected region heals. however, the bacteria can survive inside the macrophages for years until the immune system becomes weak
symptoms of TB
coughing
shortness of breath
loss of appetite
weight loss
fever
night sweats
fever and night sweats occur due to neutrophils and macrophages releasing
fever-causing substances, as part of the
inflammatory response. these chemicals affect the hypothalamus and increase core body temperature.
How can pathogens be directly transmitted in animals
Direct transmission:
- Bodily fluids
- Skin to skin contact
- Droplet infections
Inoculation:
- Break in the skin
- Animal bite
- Puncture wound
Ingestion:
- Taking in contaminated food / drink
- Transferring pathogens from hand to mouth
How can pathogens be indirectly transmitted in animals
Fromites:
Inanimate objects that are likely to carry pathogens - e.g socks
Vectors:
- Mosquitos
- Water
Factors that increase the rate of transmission of communicable disease in animals
- population density
- travel
- being immune
compromised - climate change
- damp living conditions
- waste disposal
- infrastructure
- poverty
- culture
- homelessness
- poor nutrition
Factors that prevent the spread of communicable diseases in animals
- hand washing
- improving living conditions
- disposal of both bodily and household waste effectively
How can pathogens be directly transmitted in plants
Direct contact of a healthy plant with an infected plant
Pathogen entering fruits, affecting offspring
How can pathogens be indirectly transmitted in plants
Soil contamination:
Affected plants leaving pathogens in the soil which can infect nearby plants
How might wind act as a vector for pathogens
Spores may be carried in the wind
Factors affecting the transmission of communicable diseases in plants
- susceptibility of disease
- overcrowding - density of planting
- resistance - poor mineral content of the soil reduces resistance of plants
- climatic conditions - damper, warmer
conditions increase the spread of disease - climate change
Factors that prevent the transmission of disease in plants
- space out the plants
- clear fields as thoroughly as possible
- rotate crops
- follow strict hygiene practises
What is a passive defence
One that is present before any infection, their aim is to prevent entry and spread of pathogens
what is an active defence
occur, or are enhanced, when pathogens are present
how do plants respond to an attack
receptors in the cell respond to molecules from the pathogens
stimulates release of signalling molecules that switch on genes in the nucleus
triggering cellular responses
examples of physical (passive) plant defences
- cellulose cell wall - physical barrier
- lignin thickening of cell walls - waterproof and indigestible
- waxy cuticle - prevents water from collecting on the surface
- guard cells - can close the stomata when pathogens are detected
- callose - large polysaccharide that is deposited in sieve tubes at the end of the growing season. blocks the flow so that pathogens can’t spread
- tylose formation - balloon-like swelling that fills the xylem-vessels. xylem can no longer carry water which limits pathogen spread
examples of physical (active) defences
canker - a sunken necrotic lesion in the woody tissue such as the main stem or branch. it causes the death of the cambium tissue in the bark
examples of chemical (passive) defences
tannins in bark:
deactivate salivary enzymes
examples of chemical (active) defences
- terpenoids - oils with antibacterial and antimicrobial properties. they may also create deterring scents
- phenols - these also have antibiotic and anti fungal properties. tannins found in bark inhibit attack by insects. these compounds bind to salivary proteins and digestive enzymes such as trypsin, deactivating the enzymes.
- alkaloids - nitrogen containing compounds with a bitter tase like caffeine, nicotine, cocaine and morphine. this stops herbivores feeding on them. less grazing means less exposure to pathogens
- defensins - cystein rich proteins that have broad anti-microbial activity. they appear to inhibit the action of ion transport channels
- hydrolytic enzymes - found in the spaces between cells. chitinases break down fungal cell walls, lysozymes break down bacterial cell walls
Actions that plants take when producing an active chemical response
- cell walls become thickened with additional cellulose
- callose deposited between plant cell wall and cell membrane near invading pathogen
- oxidative bursts - produce highly reactive oxygen molecules capable of damaging invading organisms
- necrosis - deliberate cell suicide. limits pathogen access to water and nutrients. brought about by injury that allowed pathogens in
what are the 2 types of immunity
inate
adaptive
examples of barriers (inate immunity) (first barrier)
skin
mucous membranes
examples of non-specific defences (inate immunity)
(second barrier)
- phagocytic leukocytes
- antimicrobial proteins
- inflammatory response
- fever
examples of specific defences (adaptive immunity)
- lymphocytes
- antibodies
- memory cells
How does the skin work as a non-specific defence
Secretes cebum (oily substance) that inhibits the growth of pathogens
Shedding of skin:
When the cell reaches the surface it has keratinised and acts as a barrier
How do expulsive reflexes work as a non-specific defence
Coughing and sneezing expel foreign objects and happen automatically
How do mucous membranes work as non-specific defences, and where are they most commonly found
Most commonly found in airways and lungs
Mucus (produced by goblet cells in epithelial layer) traps microbes and ciliated epithelial cells waft it to the back of your throat, then you swallow it.
How does the nose act as a non-specific defence
Full of hairs and mucus which trap microbes and then you blow it out or sniff it to the back of your throat and swallow it. The mucus contains lysozymes which destroy bacterial cell walls
How does the eye act as a non-specific defence
REM pushes microbes to the front of your eye
Tears contain water, salts and lysozymes
How does the ear act as a non-specific defence
Yellow sticky ear wax which traps pathogens
How does the stomach act as a non-specific defence
Microbes ingested in food enter the stomach which contain stomach acid at approx pH 2
How does the penis act as a non-specific defence
Microbes can’t usually live in urea
Urine also contains lysozymes
How does the vagina act as a non-specific defence
Moderately acidic pH (3.8-4.5)
The menstrual cycle ensures that most microbes are ejected from the vagina every 28 days with the uterine wall
How does blood clotting work
When platelets come into contact with the collagen in skin or the wall of the damage blood vessel they secrete: thromboplastin and serotonin
Thromboplastin is an enzyme that triggers a cascade of reactions. The cascade produces fibrin, this creates a mesh/network of fibres which trap platelets and blood cells to form a clot. Calcium (Ca2+) is needed alongside this.
Serotonin makes the muscle in the walls of the blood vessels contract, reducing the supply of blood to that area
The clot then dries to form a tough, hard scab that keeps pathogens out
Fibrous collagen under the scab is formed which helps to hold the sides of the cut together
Stem cells in epidermis divide to form new skin cells across the cut
New blood vessels form (angiogenesis)
Scab is released
What are lysozomes
Enzymes that disrupt the cell wall of gram-positive bacteria by digesting the peptidoglycan
What are interferons
Proteins produced by virus-infected cells in response to the virus. Interferons trigger the production of a second protein that inhibits viral replication by binding to mRNA coded for by the virus.
What is the inflammatory response and what is it characterised by
A localised response to pathogens resulting in inflammation at the site of the wound
Characterised by redness, heat, pain, and swelling of tissue
What is inflammation
The swelling of skin immediately around the rupture
How does the inflammatory response work (non-specific response)
Mast cells are activated when skin is ruptured. They release histamines and cytokines
Histamines make the blood vessels dilate, causing localised heat and redness. The raised temperature helps prevent pathogens from spreading
Histamines also make the permeability of the capillary wall increase, causing more tissue fluid (blood plasm) to be forced out of the blood - this is what causes swelling and pain
Excess tissue fluid drains into the lymphatic system – where pathogens and antigen presenting cells will come into contact with lymphocytes.
Cytokines attract phagocytes to the site which dispose of pathogens through phagocytosis
What are cytokines
Small soluble proteins that act as cell signals, particularly in the immune response
How do fevers work (non-specific response)
Normal core body temperature is 37 degrees which is controlled by the hypothalamus in the brain
During infection the large presents of white blood cells causes the hypothalamus to reset, increasing temperature
This is because pathogens cannot reproduce as quickly at temperatures above 37 degrees, and the specific immune system can work faster above 37 degrees
