Communicable Diseases Flashcards
what is a pathogen
a microorganism that causes disease. there are four types: bacteria, protists, fungi and viruses
What are communicable diseases, and how are they spread?
Caused by infectious organisms called pathogens (bacteria, viruses, fungi, protists).
Spread from one organism to another, often within the same species but can transfer between species.
Spread in plants via vectors like wind and insects.
In animals, mainly spread through direct contact.
What are bacteria, and how do they cause disease?
Prokaryotic cells with no nucleus or membrane-bound organelles.
They’re classified by shape
Also classified by cell wall type (Gram-positive = purple/blue under light microscope; Gram-negative = red).
Some bacteria release toxins that damage host cells.
How do Gram-positive and Gram-negative bacteria differ?
Gram-positive bacteria: Retain purple/blue stain (as it has a thick peptidoglycan wall).
Gram-negative bacteria: Appear red (thin peptidoglycan wall).
This classification affects how bacteria respond to antibiotics, as their cell wall structures differ.
what are viruses and how do they cause disease?
they are non living. they insert genetic material into host which takes over metabolic processes to produce more viruses until the host cell bursts. they mutate rapidly making them hard to treat
What are protists, and how do they cause disease?
Single-celled eukaryotic organisms with a nucleus.
Some are parasites, using hosts for life processes (e.g., malaria).
Enter host cells, digest them, and use their contents to reproduce.
Often spread by vectors like mosquitoes.
How do fungi cause disease in plants and animals?
Eukaryotic organisms, some multicellular, others unicellular (yeasts).
Reproduce via spores, spread rapidly, especially in plants.
fungi can’t photosynthesise so they digest food extracellularly. Digest host tissue, destroying cells and causing symptoms. Mainly affects plants as it impacts photosynthesis. In animals, produce toxins affecting host cells.
How do pathogens cause damage to the host?
1) Direct tissue damage:
Viruses take over cells, replicate, then burst out, destroying them.
Protists digest host cells and break them down.
Fungi digest and destroy host cells.
2) Producing toxins:
Bacteria release toxins that break down membranes, damage enzymes, or interfere with cell function.
Some fungi produce toxins affecting host cells.
what are the bacterial diseases in plants and animals
animals- tuberculosis, meningitis
plant- ring rot
what is tuberculosis
a bacterial disease which damages and destroys lung tissue and suppresses the immune system so the body is less able to fight other diseases
curable by antibiotics and preventable through vaccination
what is meningitis?
a bacterial disease the affects the protective membranes on the surface of the brain which can spread to the rest of the body causing blood poisoning and death. antibiotics could cure the disease if given early enough
what is ring rot?
infects a whole field meaning that it cannot be used to grow potatoes for at least 2 years
what are the viral diseases in plants and animals
animals- HIV/AIDS, influenza plants- tobacco mosaic virus
what is HIV/AIDS
a virus that targets t-helper cells in the immune system so people are more susceptible to other diseases. HIV is a retrovirsu with RNA as its genetic material. passed from person to person through bodily fluids. AIDS is what happens when HIV is left untreated. no cure but antiretroviral drugs slow the progress
what is influenza
a viral infection of the ciliated epithelial cells in the gas exchange system. it kills them leaving the airways open to secondary infection. there are three main strains a,b,c. strain a is the most virulent. they are classified further by proteins on their surface. the changed in the proteins are usually quite small between each strain so it might leave you with immunity unless their is a big change in the proteins. there is no cure but vulnerable people are given annual vaccinations to protect them against ever changing strains
what is tobacco mosaic virus
infects tobacco plants and other species including tomatoes, peppers and cucumbers;etc. it damages leaves, flowers and fruit, stunting growth and reducing yields which can lead to an almost total crop loss. there is no cure
what are the protists diseases in plants and animals
animals- malaria
plants- potato blight
what is malaria
a protist spread by the bite of infected mosquitoes (vector). its a parasite that has a complex life cycle with 2 hosts- the mosquitoes and people. it invades the RBCs, liver and the brain. the disease recurs making people weak and vulnerable to other infections. there are no cures but preventative measures can be taken (by controlling the vector). for example, insecticides, removing the water where they breed, mosquito nets, window screens
what is potato blight
a fungus which hyphae penetrates host cells, destroying leaves and fruit. no cure but careful management and chemical treatments can reduce infection risk
what are the fungal diseases in plants and animals
animals- ring worm, athletes foot
plants- black sigatoka
what is ring worm
different fungi infect different species. it causes grey-white, crusty, infectious circular areas of skin. its no damaging but may be itchy. antifungal creams are an effective cure
what is athletes foot
only affects humans. a form of human ring worm that grows on and digests the warm, moist skin between toes. causes cracking and scaling which is itchy and may become sore. antifungal creams are an effective cure
what is black sigatoka
a fungus which attacks and destroys the leaves. the hyphae penetrate and digest the cells, turning the leaves black. it can cause a 50% reduction in yield. fungicide can control the spread but there is no cure
What are the two types of pathogen transmission?
Direct transmission (contact, inoculation, ingestion) and Indirect transmission (fomites, droplets, vectors).
What are the three types of direct transmission?
Contact – e.g., kissing, skin-to-skin contact (ringworm, athlete’s foot).
Inoculation – breaks in the skin (HIV/AIDS), animal bites (rabies), sharing needles.
Ingestion – contaminated food/water (amoebic dysentery, diarrheal diseases).
What are the three types of indirect transmission?
Fomites – objects like bedding, cosmetics (athlete’s foot, Staphylococcus).
Droplet infection – expelled by coughing/sneezing.
Vectors – living organisms like mosquitoes (malaria), fleas (bubonic plague).
How can diseases spread between animals and humans?
Through direct contact, bites, food, or fomites (e.g., bird flu, brucellosis).
What factors increase disease transmission in animals?
Overcrowding, poor nutrition, weak immune system, climate change, poor sanitation, and lack of medical care.
How do plant pathogens spread?
Direct transmission – contact between infected and healthy plants.
Indirect transmission – soil, wind, water, animals, humans.
What are some examples of indirect plant pathogen transmission?
Soil contamination – bacteria/viruses remain in soil.
Wind – spores carried in the air.
Water – rain splashes spores onto leaves (e.g., potato blight).
Animals – insects and birds transmit pathogens.
Humans – spread via hands, clothing, and machinery.
What factors increase disease transmission in plants?
Susceptible crops, overcrowding, poor nutrition, damp/warm conditions, climate change.
How can plant diseases be prevented?
Crop rotation – stops pathogen build-up.
Polyculture – mixing crops to reduce spread.
Removing infected plants.
Good hygiene – cleaning tools, controlling vectors.
Chemical & biological control – fungicides, pesticides, natural predators.
How can we reduce disease transmission in humans?
Handwashing, improving hygiene and living conditions, good nutrition, disinfectants, and proper waste disposal.
How do plants recognise a pathogen attack?
Receptors detect pathogens → signal sent to nucleus which switches on genes in the nucleus
Nucleus activates defenses (e.g., chemical production, cell wall strengthening).
What are the physical defenses of plants?
Callose is released – blocks pathogen entry.
Lignin is released – strengthens cell walls.
Callose in sieve plates – seals infected areas.
Callose in plasmodesmata – stops virus spread.
What are the chemical defenses of plants?
Insect repellents – e.g., citronella.
Insecticides – e.g., pyrethrins.
Antibacterial compounds – e.g., antibiotics in plants.
Antifungal compounds – e.g., chitinases.
Toxins – e.g., cyanide.
What are the two lines of defense against pathogens in mammals?
Non-specific defences (always present, act the same way against all pathogens) and specific immune responses (target specific pathogens, slower to respond).
How does the skin act as a non-specific defence?
The skin acts as a barrier and produces sebum, which inhibits pathogen growth.
How do mucus protect against pathogens?
mucus is a sticky substance that traps microorganisms. Some mucus contains lysosomes that destroy bacterial cell walls and phagocytes that remove pathogens.
How do reflexes like coughing and sneezing contribute to non-specific defences?
They expel pathogen-laden mucus from the gas exchange system. Vomiting and diarrhea remove harmful substances from the gut.
What is the role of lysozymes in non-specific defences?
Lysozymes are enzymes found in tears, urine, and stomach acid that break down bacterial cell walls to prevent infection.
What happens during blood clotting and wound repair?
Platelets activate the enzyme thrombokinase, which leads to fibrin formation, creating a scab. Collagen strengthens the skin as it heals.
What is the inflammatory response, and what are its effects?
It is a localised response to pathogens or injury, causing inflammation, pain, heat, redness, and swelling. Mast cells release histamines (which dilate blood vessels causing localised heat to reduce pathogens from reproducing and also cause tissue fluid leakage) and cytokines (attract white blood cells for phagocytosis).
What are interferons, and how do they help in non-specific defense?
Interferons are signaling proteins produced by virus-infected cells. They help protect nearby healthy cells by:
Inhibiting viral replication within cells.
Stimulating other immune cells, such as macrophages.
Enhancing antigen presentation to activate the specific immune response.
What are phagocytes, and what are the two main types?
Phagocytes are white blood cells that engulf and destroy pathogens. The two main types are:
Neutrophils (fast-acting, short lifespan)
Macrophages (slower, long lifespan, process antigens for immune response)
What are the five stages of phagocytosis?
Pathogens release chemicals that attract phagocytes.
Phagocytes recognise non-human proteins on pathogens.
The phagocyte engulfs the pathogen in a vacuole (phagosome).
The phagosome fuses with a lysosome, forming a phagolysosome.
Enzymes in the lysosome digest and destroy the pathogen.
What are the stages of macrophage action in the immune response?
Phagocytosis – The macrophage engulfs the pathogen and encloses it in a phagosome.
Digestion – The phagosome fuses with a lysosome to form a phagolysosome, where enzymes break down the pathogen.
Antigen Processing – The macrophage processes pathogen antigens and attaches them to major histocompatibility complex (MHC) molecules.
Antigen Presentation – The macrophage displays the antigen on its surface, becoming an antigen-presenting cell (APC), which helps activate the specific immune response.
What is an antigen-presenting cell (APC)?
A macrophage that has digested a pathogen and presents its antigens on its surface using major histocompatibility complex (MHC). This helps activate the specific immune response.
What are opsonins, and how do they aid phagocytosis?
Opsonins are chemicals that bind to pathogens and “tag” them for easier recognition by phagocytes. Immunoglobulin G (IgG) and Immunoglobulin M (IgM) are the most effective opsonins.
Why is counting blood cells important in diagnosing infections?
Blood smears help identify white blood cell numbers, which indicate immune responses. High lymphocyte counts suggest a specific immune response is occurring
What are antigens?
Antigens are molecules on the surface of cells that trigger an immune response. The body distinguishes between ‘self’ and ‘non-self’ antigens.
Structure:
Made of two heavy chains and two light chains, held together by disulfide bridges.
Have a specific binding site that matches a complementary antibody for immune recognition.
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What are antibodies?
Y-shaped glycoproteins called immunoglobulins that bind to specific antigens to help neutralise or destroy them.
What are the two main types of lymphocytes?
B lymphocytes (mature in bone marrow) and T lymphocytes (mature in thymus gland).
What are the types of T lymphocytes and their functions?
A:
T helper cells – Bind to antigens on antigen-presenting cells (APCs) and release interleukins (cell-signaling molecules) that stimulate:
The activation of B cells, leading to antibody production.
The production of more T cells, amplifying the immune response.
Phagocytes, enhancing the destruction of pathogens.
T killer cells – Destroy cells infected with a pathogen by releasing perforin, which makes holes in the cell membrane. This leads to cell lysis, killing the infected cell and preventing the virus from replicating.
T memory cells – Provide long-term immunity. If the same antigen is encountered again, they divide rapidly to produce a large number of T killer cells that can quickly destroy infected cells.
T regulator cells – Suppress the immune response once a pathogen has been eliminated. They help prevent autoimmune diseases by ensuring the immune system does not mistakenly attack the body’s own cells.
T helper cells – Bind to antigens on antigen-presenting cells (APCs) and release interleukins (cell-signaling molecules) that stimulate:
The activation of B cells, leading to antibody production.
The production of more T cells, amplifying the immune response.
Phagocytes, enhancing the destruction of pathogens.
T killer cells – Destroy cells infected with a pathogen by releasing perforin, which makes holes in the cell membrane. This leads to cell lysis, killing the infected cell and preventing the virus from replicating.
T memory cells – Provide long-term immunity. If the same antigen is encountered again, they divide rapidly to produce a large number of T killer cells that can quickly destroy infected cells.
T regulator cells – Suppress the immune response once a pathogen has been eliminated. They help prevent autoimmune diseases by ensuring the immune system does not mistakenly attack the body’s own cells.
What are the types of B lymphocytes and their functions?
Plasma cells – Produce and release large amounts of antibodies that are specific to the detected antigen. These antibodies bind to antigens, neutralising them, causing agglutination (clumping pathogens together for easier destruction), and acting as opsonins to enhance phagocytosis.
B effector cells – Divide by mitosis to form plasma cell clones, ensuring a rapid immune response.
B memory cells – Remain in the body for a long time, providing immunological memory. If the same pathogen enters the body again, they rapidly divide to form plasma cells that produce antibodies, allowing for a much quicker secondary immune response.
What is the difference between the primary and secondary immune response?
The primary immune response is the initial slow immune response when the body first encounters a pathogen, taking days or weeks to become fully effective, whereas, the secondary immune response is a faster and more effective response when memory cells recognise a previously encountered pathogen.
What are the steps of humoral immunity?
1) a B lymphocyte with the correct antibody on its surface binds to a complementary antigen on a pathogen.
2) the B cell engulfs the pathogen and presents its antigens on its surface, becoming an antigen-presenting cell (APC).
3) Clonal selection - Activated T helper cells bind to the B cell APC, releasing interleukins that stimulate B cell activation. The B cell with the correct antibody is selected for cloning.
4) Clonal expansion – The selected B cell divides by mitosis to form plasma cells and B memory cells.
5) Antibody production – Plasma cells produce antibodies that:
- Neutralise pathogens by binding to antigens and preventing them from infecting cells.
- Agglutinate pathogens, meaning they cause pathogens to clump together, making them easier for phagocytes to engulf.
6) Formation of memory cells – Some cloned B cells remain as memory cells, allowing for a faster secondary immune response if the pathogen is encountered again.
What are the steps of cell-mediated immunity?
A:
1) A pathogen is engulfed by a macrophage, which processes the antigens and presents them on its surface as an antigen-presenting cell (APC).
2) T helper cells bind to the APC and recognize the antigens. The T helper cells then release interleukins to stimulate more T cells to divide.
3) Clonal expansion – The activated T helper cells rapidly divide by mitosis to form clones of T cells with receptors specific to the antigen.
4) The cloned T cells specialise into:
- T memory cells
- T killer cells
- T helper cells
- T regulator cells
what is an autoimmune disease and give examples
A condition where the immune system mistakenly attacks the body’s own cells.
Type 1 diabetes, rheumatoid arthritis, and lupus.
How does the immune system differentiate between self and non-self cells?
By recognising unique antigens on the surface of cells.
How do antibodies help defend the body?
By opsonisation (marking pathogens for destruction), neutralising toxins, and agglutination
Why do autoimmune diseases sometimes require immunosuppressant drugs?
To reduce immune system activity and prevent it from attacking the body’s own tissues.
What is the difference between natural and artificial immunity?
Natural Immunity
Active: Immunity develops after infection (memory cells provide long-term protection).
Passive: Antibodies are passed from mother to baby via placenta/breast milk (temporary protection). Early stages of breastmilk is high in colostrum which is filled with antibodies
Artificial Immunity
Active: Vaccination triggers the immune response to produce memory cells.
Passive: Pre-made antibodies are injected (short-term immunity). e.g. tetanus shot
How do vaccines provide immunity?
A weakened/inactive form of a pathogen is injected.
The immune system responds by producing antibodies and memory cells.
If exposed to the real pathogen, memory cells enable a faster and stronger immune response.
Booster vaccines may be required to maintain immunity over time.
What is herd immunity and how does it prevent disease outbreaks?
Herd immunity occurs when a high percentage of a population is vaccinated, reducing the spread of disease.
Protects those who cannot be vaccinated (e.g., newborns, immunocompromised individuals).
Helps prevent epidemics (large outbreaks in a region) and pandemics (global disease spread).
Why do some diseases not have vaccines?
Malaria – The parasite hides inside red blood cells, making it hard for the immune system to detect.
HIV – Attacks the immune system (T helper cells), making it difficult to develop lasting immunity.
What are the different types of medicines and how do they work?
Painkillers: Relieve symptoms but don’t cure diseases (e.g., paracetamol).
Anti-inflammatories: Reduce swelling and inflammation (e.g., ibuprofen).
Antibiotics: Kill bacteria but not viruses.
Antifungals: Destroy fungal pathogens.
Antibiotic resistance occurs when bacteria evolve to survive antibiotic treatment (e.g., MRSA).
Where do medicines come from, and why is biodiversity important for drug discovery?
Sources of medicines:
Penicillin – Discovered in mould (1928).
Many drugs come from plants, fungi, marine organisms, and bacteria.
Biodiversity is crucial for finding new drugs – losing species could mean losing potential cures
What is pharmacogenetics and how does it improve medicine?
Pharmacogenetics: Uses genetic information to create personalised medicine.
Example: HER2 gene in breast cancer – some treatments target this specific mutation, improving survival rates.
What is synthetic biology, and how is it used in medicine?
Genetic engineering modifies bacteria to produce needed drugs.
Mammals can be engineered for therapeutic proteins.
Nanotechnology uses tiny particles for targeted treatment.
Why are antibiotics important, and what is the antibiotic dilemma?
Antibiotics kill bacteria without harming human cells.
Reduced communicable disease deaths (36% → ~7%).
Overuse has led to resistance, making treatments less effective.
How does antibiotic resistance develop?
Random mutations make some bacteria resistant.
Natural selection favours resistant bacteria when antibiotics kill non-resistant ones.
Overuse/misuse speeds up resistance.
What are MRSA and C. difficile, and why are they problematic?
MRSA: Resistant Staphylococcus aureus, causes skin infections.
C. difficile: Affects the gut, produces toxins, spreads in hospitals.
Both thrive where antibiotics are overused.
How can we reduce antibiotic resistance?
Use antibiotics responsibly & only when needed.
Improve hygiene to prevent infections.
Isolate patients with resistant infections.
