Chapter 12 - Communicable Diseases Flashcards
What is disease caused by?
Pathogens
What are communicable diseases?
Diseases that can be passed from one organism to another
Can disease spread between species?
Yes. Most commonly, diseases is spread within a species, although it can also be spread between species
What are the 4 types of pathogens?
Bacteria
Viruses
Protists
Fungi
What are the two main ways in which bacteria are classified?
By their basic shapes
By their cell walls
How are bacteria classified by their cell walls?
There are two main types of bacteria cell walls, which have different structures and react differently under a process called Gram staining.
What are two types of cell wall classified bacteria?
Gram positive and Gram negative bacteria
Why is it useful to classify bacteria by their type of cell wall?
Because the type of cell wall affects how the bacteria reacts to different antibiotics
What do viruses do?
They invade living cells, taking the cell over to make more virus
What are bacteriophages?
Viruses that attack bacteria
What are some characteristics of viruses?
- They are considered non-living
- Absolutely tiny
- Develop adaptions according to their host
- Reproduce rapidly
What are vectors?
Something that does not cause disease itself but which spreads infection by carrying pathogens from one host to another e.g. mosquitos for malaria
What are protists?
Protists are a very diverse group of organisms. They are basically all the eukaryotes that don’t fit into the fungi, animal or plant
What is the basic structure of viruses?
Genetic material surrounded by protein
How dangerous are fungal diseases?
They are not a major problem in animals, but they can cause devastation in plants
Are fungi single or mulitcellular?
They can be both, but are most commonly multicellular
How do fungi spread?
They produce millions of tiny spores, which can spread huge distances
How do pathogenic fungi often affect plants?
They damage the leaves, which can stop them from photosynthesising, quickly killing the plant
How do viruses damage host tissues?
They take over the cell metabolism- the viral genetic material gets into the host cell and is inserted into host DNA.
New viruses are then made and burst out of the cell, destroying the cell and spreading it to other cells
How do protists damage host tissues?
They (similarly to viruses) take over cells and break them open as a new generation emerges, but they do not take over the host DNA.
They simply digest the cell content, using it to reproduce
How do fungi damage host tissues?
They digest living cells, destroying them
How do bacteria damage host tissues?
They produce toxins that poison or damage the host cells in some way
What is ring rot?
A disease of potatoes, tomatoes and aubergines caused by bacteria.
It damages leaves, tubers and fruit, and once it infects a field, crops cannot be grown in that field for 2 years
What is TMV?
A virus that infects tobacco plants and around 150 other plant species.
It damages leaves, flowers and fruit, stunting growth and reducing yield
What is potato/tomato blight?
A disease that affects potatoes and tomatoes caused by the fungus-like protist oomycete,
It penetrates the host cells, destroying leaves, tubers and fruit, causing millions of pounds of crop damage every year
What is black sigatoka?
A banana disease caused by a fungus.
They penetrate and digest cells, causing the leaves to turn black, and can cause a 50% decrease in crop yield
What is TB?
A bacterial disease that affects some mammals (including humans).
It destroys lung tissue and suppresses the immune system.
It is curable by antibiotics
What does TMV stand for?
Tobacco mosaic virus
What does TB stand for?
Tuberculosis
What is bacterial meningitis?
A bacteria infection of the protective membranes of the surface of the human brain, causing blood poisoning and rapid death
Antibiotics will cure the disease if delivered early
What is HIV/AIDS?
A virus that affects human as well as some primates, which gradually destroys the immune system of the host. It is commonly spread through unprotected sex.
There is no vaccine or cure.
What is influenza?
A viral infection that kills epithelial cells in gaseous exchange, leaving the airways open to secondary infection (such as from pneumonia).
Vulnerable groups are given a flu vaccine annually, however there is no cure
What are the 3 strains of influenza, and which is the most dangerous?
There are strains A, B and C.
The most dangerous is strain A.
What is malaria?
A disease caused by protists and spread by mosquito bites. It is extremely deadly, and is responsible for 600,000 deaths every year.
There are limited cures and no vaccine, however preventative measures such as insecticides and mosquito nets work
What is ring worm?
A fungal disease affects some mammals (including humans). It is typically a grey-white crusty area of skin.
It is not damaging, but is unsightly and often itchy.
Anti-fungal creams are effective
What is athletes foot?
A human fungal disease, which is another form of ring worm that grows between toes. It causes cracking and scaling, and is often itchy and sore.
Anti-fungal creams are effective
What are the 3 main ways of direct transmission?
- Direct contact
- Inoculation
- Ingestion
What is direct transmission?
When pathogens are transferred directly from one individual to another
Examples of direct contact
- Kissing or transfer of bodily fluids
- Direct skin to skin contact (often for fungal infections e.g. ringworm)
Examples of inoculation
- Through a break in the skin
- From an animal bite
What is ingestion?
When contaminated food or drink is eaten/drunk, or when pathogens being transferred from hands to mouth
What are the two types of transmission?
Direct and indirect transmission
What are fomites?
Inanimate objects on which pathogens can exist, and hence can transfer pathogens
What is droplet infection?
When tiny droplets of saliva and mucus which contain pathogens are expelled from your mouth, and a healthy individual inhales these droplets
What are the two main things that act as a vector?
Water
Animals
What 3 factors must be present for a disease to spread?
- Pathogen
- Susceptible hosts
- Favourable environment
What are some factors that increase rate of transmission of communicable diseases in animals?
- Overcrowded living and working conditions
- Poor sanitation
- Climate conditions advantageous for the pathogen
Examples of plant disease that can be spread through direct contact
Ring rot
Blight
What two ways can plant disease be spread through indirect transmission?
Soil contamination
Vectors
How are plant diseases spread through soil contamination?
Infected plants leave pathogens or reproductive spores in the soil, which can spread to the next plant
What are the 4 vectors that help spread plant disease?
- Wind
- Water
- Animals
- Humans
How does wind spread plant disease?
Pathogens may be carried by the wind to new plants
How does water spread plant disease?
Pathogens can be spread by being carried in moving water to new plants
How do animals spread plant disease?
Insects and birds can carry pathogens from one plant to another as they feed
How do humans spread plant disease?
Pathogens can survive and be spread by hands, clothing and many different fomites.
They can also be spread over large distances, sometimes internationally, through the trade of plants and crops
What factors can increase the transmission of disease in plants?
- Planting crops that are susceptible to disease
- Poor mineral nutrition weakens immune resistance of plants
- Damp and warm conditions
In plant defence against pathogens, what two things cause receptors in the cell to respond?
Receptors can recognise and respond to molecules from the pathogen, or respond to chemicals produced when the plant cell wall is attacked directly.
What do plant receptors then stimulate?
Plant receptors stimulate the release of signalling molecules, that switch on genes in the nucleus.
What does the switching on of genes in the nucleus do in plant defence against pathogens?
It triggers cellular responses
What are the different cellular responses in plant defence against pathogens?
- Producing defensive molecules that directly attack the pathogen
- Producing defensive chemicals that send alarm signals to unaffected cells to trigger their defences
- Physically strengthening cell walls
What is made to help physically strengthen cell walls?
Polysaccharides (callose and lignin) are produced on the nucleus’ command to help strengthen plant cell walls to defend against the pathogen
What is the role of callose in plant defence against pathogens?
Callose acts as a barrier, preventing pathogens from entering plant cells around the site of infection.
Where is callose deployed when plant defence is triggered?
- Large amounts of callose continue to be deposited in cell walls after the initial infection
- Callose blocks sieve plates in the phloem, sealing of infected areas, preventing the spread of pathogens
- Callose is deposited in the plasmodesmata between infected cells and their neighbours, further preventing the pathogen from spreading from cell to cell
What is the deployment of callose and lignin an example of?
Plant physical defences
3 examples of chemical defence in plants
- Antifungal compounds such as phenols
- Insect repellents such as pine resin
- Cyanides
What defences do we have to keep pathogens out?
- The skin, that blocks pathogens from entering the body
- Mucous membranes that secrete sticky mucus, which traps microorganisms
- Lysozymes that are found in various areas of the body, such as in tears, urine and stomach acid
What do lysozymes do?
They destroy bacteria that attempt to enter our body through these passageways
How do explusive reflexes help defend against pathogens?
- Coughs and sneezes ejected pathogen-laden mucus from the gas exchange system
- Vomiting and diarrhoea expel contents of the gut along with any infective pathogens
Why are blood clots sealing wounds important?
Because when you cut yourself, the skin is breached and pathogens can enter the body
What does platelets come into contact with?
Collagen in the skin or the wall of damaged blood vessels
What are the most important substances secreted from the contact between collagen and platelets?
Thromboplastin
Serotonin
What is thromboplastin?
An enzyme that triggers a cascade of reactions that result in the formation of a blood clot
What does serotonin do?
It makes the smooth muscle in the walls of the blood vessels contract, so they narrow and reduce blood flow in that area, minimising blood loss
What happens during wound repair?
- A hard tough scab is formed that keeps pathogens out
- Epidermal cells below the scab start to grow, sealing the wound
- Damaged blood vessels regrow, and collagen fibres are deposited to give tissue strength
- Once the new epidermis reaches normal thickness, the scab comes off
What is inflammation characterised by?
Pain, heat, redness and swelling
What are the cells that are activated in damaged tissues which cause inflamation?
Mast cells
What 2 types of chemicals do mast cells release?
- Histamines
- Cytokines
What do histamines do in inflammatory response?
- Make blood vessels dilate, locally raising temperature and redness- this raised temperature helps prevent pathogens from reproducing
- Make blood vessel walls more leaky so blood plasma is forced out, becoming tissue fluid and causing swelling and pain
Why are fevers useful for defending against pathogens?
- Higher temperature inhibit most pathogens’ reproduction rate
- The specific immune system works faster in higher temperatures
What are the two main types of phagocytes?
Neutrophils
Macrophages
What does pus consist of?
Dead neutrophils and pathogens
What is the first step of phagocytosis?
Phagocytes are attracted by chemicals produced by the pathogen
What is the second step of phagocytosis?
Phagocytes recognise non-human proteins on the pathogen- this is not a response to a specific type of pathogen, but rather a response to a cell or organism that is non-self
What is the third step of phagocytosis?
The phagocytes engulf the pathogen
What is the vacuole of phagocytes called, in which pathogens are when engulfed?
The phagosome
What do cytokines do in inflammatory response?
Attract phagocytes to the site of inflammation
What is the fourth step of phagocytosis?
Enzymes from the lysosome digest and destroy the pathogen
How long does it usually take a human neutrophil to complete phagocytosis?
Under 10 minutes
Does phagocytosis take longer for neutrophils or macrophages?
It takes longer for macrophages, as it is a more complex process
What does the MHC complex stand for?
The major histocompatibility complex
What does the MHC complex do?
It moves pathogen antigens from a digested pathogen to the macrophages own surface membrane
After the MHC complex has moved the antigens to its own surface membrane, what does the macrophage become known as?
An antigen-presenting cell (APC)
What is the effect of the formation of an APC?
It stimulates other cells involved in the specific immune system response
How can you identify if a non-specific or specific immune response is taking place through blood smears?
By identifying the number of different types of lymphocytes in the blood smear
What do cytokines do?
- They act as cell-signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection/inflammation
- They can also increase body temperature
What do opsonins do?
Opsonins are chemicals that bind to pathogens and ‘tag’ them so they are more easily identified by phagocytes.
Phagocytes have receptors on their cell membranes that bind to common opsonins, which results in the phagocytes engulfing the pathogen
What are antibodies?
Y-shaped glycoproteins called immunoglobulins
How many types of antibody are there?
There are millions of types of antibodies, as there is a specific antibody for every antigen
What are antibodies made up of?
Two identical long polypeptide chains called the heavy chains, and two much shorter identical chains called the light chains
What are chains held together by?
Disulphide bridges
In what way do antibodies bind to antigens?
With the ‘lock and key’ mechanism, similar to enzymes and substrates
What is the variable region on antibodies?
The binding site, which is an area of 110 amino acids on both the heavy and light chain.
It is a different shape on each antibody, hence is known as the variable region
What is the constant region on antibodies?
The area other than the binding site, which is always the same, hence is known as the constant region
When an antibody and antigen bind together, what is formed?
An antigen-antibody complex
What does the antibody in the antigen-antibody act as and what does this do?
It acts as an opsonin, hence signalling the phagocytes, allowing the antigen to be engulfed and destroyed
What can most pathogens no longer to once an antigen-antibody complex is formed?
They can no longer effectively invade host cells once an antigen-antibody complex is formed
What are agglutinins?
Antibodies can act as agglutinins, which causes pathogens with antigen-antibody complexes to clump together, helping prevent them from spreading further and making it easier for phagocytes to engulf large numbers of pathogens at once
What do anti-toxins do?
Antibodies can act as anti-toxins, which bind to toxins produced by pathogens, making them harmless
What are the white blood cells that the specific immune response is based on called?
Lymphocytes
Where do B lymphocytes mature?
Bone marrow
Where do T lymphocytes mature?
The thymus gland
What are the 4 main types of T lymphocytes?
- T helper cells
- T killer cells
- T memory cells
- T regulator cells
What are the 3 main types of B lymphocytes?
- Plasma cells
- B effector cells
- B memory cells
What is the function of T helper cells?
They have CD4 receptors on their cell-surface membranes, which bind to the surface antigens of APCs, and produce interleukins
What are interleukins?
A type of cytokine made by T helper cells, which:
- stimulate the activity of B cells (increasing anti-body production)
- stimulate the production of other types of T cells
- attract and stimulate macrophages to ingest pathogens with antigen-antibody complexes
What is the function of T killer cells?
They destroy the pathogen. They produce a chemical called perforin, which kills the pathogen
How does perforin kill pathogens?
By making holes in the cell membrane, making it freely permeable
What is the function of T memory cells?
They are part of the immunological memory, and if they meet the same antigen a second time, they can rapidly divide to form a huge number of T killer cells specialised for that antigen
What is the function of T regulator cells?
They control and regulate the immune system. For example, they stop the immune response once a pathogen has been eliminated, and makes sure the body recognises self antigens, so as to prevent autoimmune responses
What are autoimmune responses?
Immune responses by an organism against its own healthy cells and tissues, which occurs when the immune system stops recognising its own cells.
What is the function of plasma cells?
They produce antibodies to a particular antigen and release them into circulation
What is the function of B effector cells?
They divide to form plasma cells
How long does an active plasma cells live?
Only a few days, however while active they produce around 2000 antibodies per second
What is the function of B memory cells?
They are programmed to remember a specific antigen and enable the body to make a very rapid response when a pathogen carrying that antigen is encountered again
What is cell-mediated immunity?
Where T lymphocytes respond to altered cells
What are some examples of altered cells that can trigger cell-mediated immunity?
APC macrophages
Cancer cells
What is the first step in cell-mediated immunity in response to APCs?
CD4 receptors on T helper cells binds to the antigens on the APC, causing the T helper cells to become activated and produce interleukins
What happens after the interleukins are produced by the initial T helper cell in cell-mediated immunity?
The interleukins stimulate the cloning of more activated T helper cells, and other T cells
What may the cloned T helper cells do?
- Differentiate into memory cells
- Differentiate into T killer cells
- Produce more interleukins that stimulate phagocytosis
- Produce more interleukins that stimulate B cells division
What are the main differences between humoral and cell-mediated immunity?
- Humoral is mainly associated with B lymphocytes, whereas cell-mediated is mainly associated with T lymphocytes
- Humoral secretes antibodies to fight against antigens, whereas cell-mediated immunity secretes cytokines and no antibodies to attack the pathogens
What is the first step of humoral immunity?
Clonal selection
What is clonal selection?
Where the B cell with the correct antibody for a particular antigen binds to the pathogen and becomes a B-APC. This is the B cell that will go on to undergo clonal expansion
What is the step in humoral immunity after clonal selection?
T helper cells recognise and bind to the B-APC, which activates them, and causes them to release interleukins
What happens when the interleukins are released in humoral immunity?
The interleukins produced by the T helper cells activate the B cells
What happens after the B cells are activated by the interleukins in humoral immunity, and what is this known as?
The activated B cells clone themselves and differentiate into plasma cells and memory cells.
This is called clonal expansion
What do the cloned plasma cells do in humoral immunity?
They produce antibodies that fit the antigens of the pathogen, which bind to the antigens and disable them, or act as opsonins or agglutinins.
What is the production of antibodies in humoral immunity known as?
The primary immune response
How long does the primary immune response in humoral immunity take and what does this mean for recovering from illness?
The primary immune response can take days or even weeks to become fully effective against a pathogen; this is why we get ill, and why it takes time to recover.
What is the secondary immune response in humoral immunity?
Some of the cloned B cells differentiate into B memory cells, meaning if the body is infected by the same pathogen again, B memory cells can rapidly divide to form many B plasma cell clones, making the primary immune response much faster
What seems to cause autoimmune diseases in some cases?
T regulator cells not functioning effectively
What is a treatment for autoimmune diseases, but what is the problem with this treatment?
Immunosuppressant drugs can be used to prevent the immune system from working, however this makes the patient vulnerable to disease, as their natural immune defence is gone
What are 3 common examples of autoimmune diseases?
- Type 1 diabetes
- Rheumatoid arthritis
- Lupus
What is natural active immunity?
Where the body actively acts to produce something (e.g. antibodies or memory cells) to fight pathogens
What is colostrum?
The first milk a mammalian mother makes, which is very high in antibodies
How are new-born babies protected from pathogens despite having an immature immune system that cannot create antibodies?
- Some antibodies enter the fetus while the baby is still in the uterus
- The milk of the mother is very high in antibodies which are passed down from the mother, so are likely to be relevant to pathogens in its environment
- This results in just a few days after birth, a breast-fed baby having the same level of antibody protection as the mother
What is the process of mothers giving antibodies to new-borns an example of?
Natural passive immunity, as the baby is passively receiving the protection against pathogens
What is artificial passive immunity?
Where antibodies are formed in one individual (often an animal), extracted and then injected into the blood stream of another individual. This immunity is temporary but can be life saving
What is artificial active immunity?
Where a safe form of an antigen (a vaccine) is injected into the bloodstream, and the immune response causes memory cells to form, resulting in a faster immune response if the real pathogen is ever present
What different types of antigen are considered safe?
- Killed or inactive bacteria or viruses
- Attenuated (weakened) strains of live bacteria or viruses
- Toxin molecules that have been detoxified
- Isolated antigens extracted from the pathogen
- Genetically engineered antigens
What happens when the safe antigen is injected?
The foreign antigens trigger the humoral immune response, producing antibodies and memory cells as if you were injected with the real thing.
Then if you do end up coming into contact with the live pathogen, you have memory cells saved which can allow a rapid immune response, shutting it down before it causes damage
How long does artificial active immunity last?
It can last from a year to a lifetime. Sometimes boosters (repeat vaccinations) are needed to maintain immunity
What is an epidemic?
When a communicable disease spreads rapidly to a lot of people at a local or national level
What is a pandemic?
When a communicable disease spreads rapidly across a number of countries and continents
Two examples of diseases that there is no vaccine for yet
Malaria
HIV
What was the first widely used antibiotic?
Penicillin
Where does penicillin come from?
A type of mould
How do scientists use computer programs to design drugs?
They can build 3D models of key molecules in the body, and of pathogens and their antigen system.
This allows models of potential drug molecules to be built up and tested digitally
Where are most of the drugs commonly used in medicine derived from?
Bioactive compounds from plants, microorganisms and other forms of life
How does loss of biodiversity affect medicine?
Because plants, animals and microorganisms that are being destroyed could give us the key to a life saving drug, as most medicines are derived from natural compounds
What is pharmacogenetics?
The science of combining knowledge of drugs with personal genetic material, to create personalised medicine
What can synthetic biology be used for?
Using genetic engineering techniques, we can develop populations of bacteria to produce in demand drugs that would otherwise be too rare, expensive or unavailable
What is nanotechnology?
A strand of synthetic biology, where tiny, non-natural particles are used for biological purposes e.g. to deliver drugs to very specific sites
What is wrong with the overuse of antibiotics?
With greater use of antibiotics, more and more bacteria become resistant to more and more types of antibiotic
How can antibiotic-resistant infections be reduced in the long term?
- Minimise the use of antibiotics, and when they are used ensure that the entire course is completed
- Good hygiene in key places like hospitals and care homes
