Communicable Diseases Flashcards
What is meant by the term ‘communicable disease’?
Disease that can be passed from one organism to another
What are the types of pathogens?
- Bacteria
- Viruses
- Fungi
- Protistica
What 2 ways can bacteria be classified?
- By their basic shapes (rod, spherical, comma, spiralled, corkscrew)
- By their cell walls (gram staining)
Gram + will look blue
Gram - will look red
What are viruses called that attack bacteria?
Bacteriophage
How do viruses damage the host tissues?
- Directly
- They take over the cell metabolism
- The viral genetic material gets into the host cell and is inserted into the host DNA
- The virus then uses the host cell to make new viruses which then burst out of the cell and spread to infect other cells
How do protists damage the host tissues?
- Directly
- Similar to viruses, these also take over cells and break them open as the new generation emerge
- However, they don’t take over the genetic material of the cell
- They simply digest and use the cell contents as they reproduce
How does fungi damage the host tissues?
- Directly
- They digest the living cells and destroy them
What are 4 example plant diseases?
- Ring Rot
- Tobacco Mosaic Virus
- Potato Blight
- Black Sigatoka
How does bacteria damage the host tissues
- Produces toxins
- These poison or damage the host cells
- By either breaking down cell membrane, inactivating enzymes or interfering with the host cells genetic material so the cells can’t divide
What is ring rot?
- A bacterial disease
- It damages leaves, tubers and fruit
- There is no cure
- Once it affects a field it cannot be used to grow potatoes again for at least 2 years
What is tobacco mosaic virus (TMV)?
- A virus
- Yellow discolouration of leaves
- Resistant crop strains are available but there is no cure
What is potato blight?
- A protist
- Purple/brown blotches on leaves
- There is no cure but resistant strains and chemical treatments can reduce infection risk
What are the 7 examples of animal diseases?
- TB
- Bacterial Meningitis
- HIV/AIDS
- Flu
- Malaria
- Ring worms
- Athlete’s foot
What is Black Sigatoka?
- Fungal infection
- Black leaves
- Resistant strains are being developed - Good husbandry and fungicide treatment can control the disease but there is no cure
What is Tuberculosis (TB)?
- Bacterial disease
- Destroys lung tissue
- Suppresses immune system
- Curable (antibiotics) and preventable (by improving living standards and vaccination)
What is Bacterial Meningitis?
- Bacterial infection
- Affects meninges of the brain, which can spread to the rest of the body causing blood poisoning (septicaemia) and rapid death
- Antibiotics will cure the disease if delivered early
- Vaccines can protect against some forms of it
What is HIV-AIDS?
- Human immunodeficiency virus
- Targets immune system
- Passed from one person to another in bodily fluids, such as unprotected sex, shared needles, contaminated blood products and from mothers to babies during pregnancy, birth or breastfeeding
- No vaccine and no cure, but anti-retro viral drugs slow the process of the disease to give many years of healthy life
What is influenza (flu)?
- Viral infection
- Kills ciliated epithelial cells in gas exchange system
- Leaves airways open to secondary infection (e.g. pneumonia)
- There is no cure but there is a vaccine
What is malaria?
- Caused by protists
- Causes a flu-like illness
- Spread by bites of infected mosquitoes
- There is no vaccine or cure but there are preventative measures
- E.g. insecticides, removing standing water where they breed, mosquito nets, window and door screens and long sleeved clothing
What is ring worm?
- Fungal disease
- Causes a ring-shaped rash
- Antifungal creams are an effective cure
How are pathogens directly transmitted in animals?
- Direct contact (kissing, contact with bodily fluids, skin to skin contact, microorganisms from faeces)
- Inoculation (through a break in skin, from animal bite, sharing needles)
- Ingestion (taking in contaminated food or drink or transferring pathogens from hands to mouth)
How are pathogens indirectly transmitted in animals?
- Fomites (inanimate objects such as bedding, socks or cosmetics)
- Inhalation (minute droplets of saliva and mucus expelled from mouth when you talk, cough or sneezed)
- Vectors (transmits communicable pathogens from one host to another, e.g. water)
What 7 factors affect the transmission of communicable diseases in animals?
- Overcrowded living/working conditions
- Poor nutrition
- A compromised immune system (HIV)
- Poor disposal of waste (breeding site for vectors)
- Climate change (introduce new vectors and diseases)
- Culture and infrastructure (some traditional medical practices can increase transmission, e.g. FGM increase HIV)
- Socioeconomic factors (lack of trained health workers etc)
How are pathogens directly transmitted in plants?
Direct contact of a healthy plant with any part of a diseased plant
How are pathogens indirectly transmitted in plants?
- Soil contamination (infected plants often leave pathogens or reproductive spores in soil
- Vectors:
• Wind - oomycete spores may be carried
• Water - spores swim on surface film of water on leaves
• Animals - insects and birds carry pathogens and spores from one plant to another as they feed
• Humans - pathogens and spores are transmitted by hands, clothing, fomites, farming practices and by transporting plants and crops around the world
What 5 factors affect the transmission of communicable diseases in plants?
- Planting crops that are susceptible to disease
- Over-crowding = more contact
- Poor mineral nutrients = less resistance
- Damp, warm conditions = pathogens survive and spread
- Climate change (increased rainfall and wind) = promote spread
Physical defences of plants?
- Deposits callose
- Synthesised and deposited between cell walls, membrane and plasmodesmata next to infected cell
- It blocks sieve plates in phloem, sealing off infected part and preventing spread
- Lignin added = structural support
- Callose continues to be deposited after initial infection
Chemical defences of plants?
- Insect repellents
- Insecticides
- Antibacterial compounds (antibiotics)
- Antifungal compounds
- Anti-oomycetes
- General toxins
What is athlete’s foot?
- Fungal disease
- Can cause cracking and scaling between toes , which is itchy and may become sore
- Antifungal creams are an effective cure
What barriers does the body have to stop the entry of pathogens?
Skin:
- Skin produces sebum, an oily substances that inhibits growth of pathogen
Body tracts lined with mucous membranes:
- Secrete sticky mucus to trap microorganisms
- Contains lysosomes which destroy bacterial and fungal cell walls
Lysosomes:
- In tears, urine and stomach acid, prevent pathogens getting into body
Expulsive reflexes:
- E.g. coughs, sneezes, vomiting and diarrhoea
Blood clotting?
- Non-specific defence
- Thromboplastin, an enzyme that triggers a cascade of reactions resulting in the formation of a blood clot
- Clot dries out, forming a scab to keep pathogens out
Inflammatory response?
- Non-specific defence
- Mast cells activated in damaged tissue and release chemicals (histamines and cytokines)
- Histamines make blood vessels dilate, causing heat and redness. The raised temp prevents pathogens reproducing
- Histamines make blood vessels walls more leaky so blood plasma is forced out (then known as tissue fluid). The tissue fluid causes swelling and pain
- Cytokines attract WBC (phagocytes) to the site. They dispose of pathogens by phagocytosis
What is a macrophage and what does it do?
- A type of WBC that kills microorganisms (phagocyte)
- Takes longer to engulf and destroy a bacterium in comparison to a neutrophil
- Once pathogen is digested, it combines antigens from pathogen surface membrane with special glycoproteins in cytoplasm, called the major histocompatibility complex (MHC)
- The MHC moves the pathogen antigens to macrophage’s surface membrane
- Becomes an antigen-presenting cell (APC)
- Antigens now stimulate other cells involved in the specific immune system response
What is the major histocompatibility complex?
A collection of genes that creates an APC
If pathogens get into body, what are the next lines of defence?
- Fevers:
• Cytokines stimulate hypothalamus to reset thermostat and your temp goes up. This is useful because most pathogens reproduce best at 37°C or below and the specific immune system works faster at higher temps - Phagocytosis:
• Pathogens produce chemicals that attract phagocytes
• Phagocytes recognise non-human proteins on pathogen
• The phagocyte engulfs the pathogen and encloses it in a vacuole called a phagosome
• The phagosome combines with a lysosome to form a phagolysosome
• Enzymes from lysosome digest and destroy pathogen
What are cytokines?
Chemicals that act as cell-signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection or inflammation
They can also increase body temp and stimulate the specific immune system
What are opsonins?
Chemical that bind to pathogens and ‘tag’ them so they can be more easily recognised by phagocytes
What do agglutinins do?
Stick pathogens together to stop spread and makes it easier to engluf
What are antibodies?
- Y-shaped glycoproteins
- Binds to a specific antigen on the pathogen
What’s it called when an antibody binds to an antigen?
An antigen-antibody complex
How do antibodies defend the body?
Opsonin:
- Binds to pathogen and releases chemicals that attract phagocytes
Agglutinins:
- Stick pathogens together to stop the spread
- Easier to engulf
What is the specific immune system based on?
WBC called lymphocytes
- B lymphocytes mature in the Bone marrow
- T lymphocytes mature in the Thymus gland
What are the main types of T lymphocytes?
- T helper cells
- T killer cells
- T memory cells
- T regulator cells
What are the main types of B lymphocytes?
- Plasma cells
- B effector cells
- B memory cells
What are T helper cells?
- Produce interleukins (cytokine), these:
- Stimulate activity of B cells
- Stimulate production of other types of T cells
- Attracts and stimulates macrophages
What are T killer cells?
- Destroy pathogen carrying the antigen
- Produce a chemical called perforin, which kills the pathogen by making holes in the cell membrane so it’s freely permeable
What are T memory cells?
- Live for a long time and are part of the immunological memory
- If they meet an antigen a second time, they divide rapidly to form a huge number of clones of T killer cells that destroy the pathogen
What are T regulator cells?
- Suppress immune system, acting to control and regulate it
- Stop immune response once pathogen has been eliminated
- Prevents an autoimmune response
What are plasma cells?
- They produce antibodies to a particular antigen and release them into circulation
- an active plasma cell only lives for a few days but produces around 2000 antibodies per second while it’s alive and active
What are B effector cells?
Divide to form the plasma cell clones
What are B memory cells?
- Live for a very long time and provide the immunological memory
- 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
Describe the cell-mediated response
- Macrophages engulf and digest pathogens in phagocytosis
- They process the antigens from surface of pathogen to form antigen-presenting cells (APCs)
- Receptors on some of the T helper cells fit antigens
- These T helper cells become activated and produce interleukins, which stimulate more T cells to divide rapidly by mitosis
- They form clones of activated T helper cells that all carry the right antigen to bind to a particular pathogen
- The cloned T cells may:
• Develop into T memory cells
• Produce interleukins to stimulate phagocytosis
• Produce interleukins to stimulate B cells to divide
• Stimulate development of T killer cells
Describe humoral immunity
- B cell with complementary antibodies engulfs and processes antigens to become APC
- T helper cells bind to antigens on APC (clonal selection)
- Interleukins, produced by T cells, activate other B cells
- B cells divide by mitosis, forming clones of plasma cells and B memory cells (clonal expansion)
- Plasma cells produce specific antibodies that disable pathogens, or act as opsonins or agglutinins (PRIMARY IMMUNE RESPONSE)
- B memory cells form plasma cells to produce specific antibody
- If same pathogen invades, cloned B memory cells divide into plasma cells (SECONDARY IMMUNE RESPONSE)
What is an autoimmune disease?
When the immune system stops recognising ‘self’ cells and starts to attack healthy body tissue
Give 3 examples of autoimmune diseases
- Type 1 diabetes
- Rheumatoid arthritis
- Lupus
What body part is affected from type 1 diabetes?
The insulin-secreting cells of the pancreas
What is the treatment for type 1 diabetes?
- Insulin injections
- Pancreas transplants
- Immunosuppressant drugs
What body parts are affected from rheumatoid arthritis?
- Joints, especially in the hands, wrists, ankles and feet
What are the treatments for rheumatoid arthritis?
- No cure
- Anti-inflammatory drugs
- Steroids
- immunosuppressants
- Pain relief
What body part is affected from lupus?
- Often affects skin and joints, causing fatigue
- Can attack any organ in body, including kidneys, liver, lungs or brain
What treatments are there for lupus?
- No cure
- Anti-inflammatory drugs
- Steroids
- Immunosuppressants
- Various others
What is natural active immunity?
- When you meet a pathogen for the first time, your immune system is activated and antibodies are formed = destruction of antigen
- The immune system produces T and B memory cells so if you meet the pathogen for a second time, your immune system recognises it and immediately destroys it
What is natural passive immunity?
- The immune system of a new born baby is not mature and it can’t make antibodies for the first couple of months
- Some antibodies cross the placenta from the mother to her foetus while the baby is in the uterus, so it has some immunity to disease at birth
- The first milk a mammalian mother makes is called colostrum, which is high in antibodies
- The infant gut allow these glycoproteins to pass into the bloodstream without being digested
Describe artificial passive immunity
- Antibodies are formed in one individual (often an animal), extracted and then injected into the bloodstream of another individual
- Gives temporary immunity, it doesn’t last long but can be life saving
- E.g. tetanus (antibodies extracted from blood of horses) and rabies is another example
Describe artificial active immunity
The immune system is stimulated to make its own antibodies to a safe form of an antigen (a vaccine) which is injected into the bloodstream
How does a vaccination work?
1- The pathogen is made safe so that the antigens are intact but there’s no risk of infection. Vaccines may contain:
• Killed or inactivated bacteria/viruses
• Weakened strains of live bacteria/viruses
• Toxin molecules that have been altered/detoxified
• Isolated antigens extracted from pathogen
• Genetically engineered antigens
2- Small amounts of the safe antigen are injected into blood
3- Primary immune response is triggered by foreign antigens and the body produces antibodies and memory cells
4- If you come into contact with live pathogen, the secondary immune response is triggered and you destroy the pathogen rapidly before symptoms appear
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
What is herd immunity?
When a significant number of people in the population have been vaccinated so those who don’t have immunity are protected
What is the source of penicillin and what does it do?
- Source = commercial extraction originally from mould growing on melons
- Action = antibiotic, the first effective treatment against many common bacterial diseases
What is the source of aspirin and what does it do?
- Source = based on compounds from willow bark
- Action = painkiller, anti-coagulant (blood thinner), anti-pyretic (reduces fever) and anti-inflammatory
What is the source of digoxin and what does it do?
- Source = based on digitoxin, originally extracted from foxgloves
- Action = powerful heart drug used to treat atrial fibrillation and heart failure
What is pharmacogenetics?
The science of interweaving knowledge of drug actions with personal genetic material
What is synthetic biology?
A field of science that involves redesigning organisms for useful purposes by engineering them to have new abilities
How has antibiotic resistance developed?
If a random mutation, during bacterial reproduction, produces a bacterium that is not affected by the antibiotic, that is the one best fitted to survive and reproduce, passing on the antibiotic resistance mutation to the daughter cells
Give 2 examples of antibiotic-resistant bacteria
- MRSA
- C.difficile
What is MRSA?
- A bacterium carried by up to 30% of the population on their skin or in their nose
- In the body it can cause boils, abscesses, and potentially fatal septicaemia
- Was treated effectively with methicillin but mutation has produced methicillin-resistant strains
What is C.difficile?
- A bacterium in the guts of about 5% of the population
- Produces toxins that damage lining of intestines, leading to diarrhoea, bleeding and even death
- Not a problem for healthy person but when commonly-used antibiotics kill off much of the ‘helpful’ gut bacteria, it survives, reproduces and takes hold rapidly
How can antibiotic-resistant infections be reduced in the long term?
- Minimising use of antibiotics and ensuring every course of antibiotics is completed to reduce risk of resistant individuals surviving and developing
- Good hygiene in hospitals, care homes and in general
