Communicable diseases, Disease Prevention & The Immune system

Autoimmune Diseases

Autoimmune diseases are diseases that evolve when a person or animal's immune system attacks a part of the host body, in absence of pathogenic infection. During clonal selection, lymphocytes that are programmed to attack 'self' are normally destroyed before entering the bloodstream.

Phagocytes

Phagocytes are a type of white blood cell (WBC), whose role is to trap pathogens and kill them. •• Pathogens can be recognized as foreign by chemicals markers on outer membrane called antigens •• These are specific to the organism •• Proteins in the blood, called antibodies, attach to these foreign antigens Phagocytes contain phagosomes: membrane bound organelles, which act as receptors, binding antibodies to the already pound pathogens. They may be assisted by proteins called opsonins.

Primary defences Secondary defences Non-specific defences Specific defences

are those that prevent pathogens from entering the body. are those that prevent pathogens from harming the body once it has infected the host. are those which occur in the same way, no matter the pathogen, and don't require identification of the antigen. are immune responses carried out by the host which specifically target the pathogen.

Vaccination

provides a way of artificially stimulating primary immune response without the risk of illness •• Exposes immune system to the antigen ○○Attenuated pathogen ○○Isolated antigen •• Allows the body to produce adapted memory cells •• Allows for demonstration of secondary response when next exposed to the virus

Bacteria

• Can rapidly multiply in the right conditions • Cause disease by damaging cells or producing toxins that are harmful • Eg tuberculosis, bacterial meningitis, ring rot (plants)

Malaria

• Eukaryotic organism • Plasmodium falciparum • Spreads by vector • Malarial parasites live in red blood • Feed on hemoglobin • Mosquito will suck parasitical gametes into its stomach • Gametes fuse to form zygotes in mosquito stomach • Plasmodium develops and moves to salivary glands • Mosquito bites person, injecting saliva • Plasmodium enters person • Migrates to liver • Multiplies and passes into blood • Cycle repeats • Kills 3 million annually • limited to regions where anopheles mosquito can live

Protoctista

• Feed on cell contents as they grow • Eg malaria, potato blight

Fungi

• In animals, cause redness and irritation • This is due to hyphae released from the fungus • Eg black sigatoka (bananas), ringworm (cattle), athlete's foot

Viruses

• Invade cells and take over the protein-synthesising organelles • Infect the cells with new DNA • Host cells eventually burst and release new copies of the viral DNA • Eg HIV/AIDS, influenza, tobacco mosaic virus (plants)

Active defences

• Leaves sense presence of pathogens • Begin to prioritise use of energy in secreting harmful chemicals • Cellulose produced to further fortify the cell walls • Oxidative bursts: produce harmful oxygen molecules to target the pathogen

Tuberculosis

• Mycobacterium tuberculosis • Divides slowly (every 20 hours) • Can survive for 6 months outside body • Sufferer cough, catapulting droplets of saliva into air • Saliva contain tuberculi bacilli • High speed • Reach over 1-2m • 1 sneeze can have up to 40,000 droplets • worldwide • 1% of world newly infected each year

Plant Defences Against Pathogens- Physical barriers

• Passive: •• Cellulose cell wall •• Lignin thickening of cell walls ••Waxy cuticles •• Bark •• Closed stomata •• Callose ○○Large polysaccharide deposited in sieve plates in phloem ○○Block movement of pathogens up and down plants to avoid infection of the entire plant •• Tylose ○○Balloon-like swelling in xylem ○○Blocks xylem and stops pathogens from travelling this way around the plant

Production of chemicals

• Passive: •• Terpenoids •• Phenols •• Alkaloids •• Hydrolytic enzymes

Climate/ Environment

• Some vectors only live in hot climates, e.g. mosquitos carrying malaria •Many viruses, protoctists and bacteria survive better in warm climates • Very cold climates can kill pathogens Environment • Cramped and crowded environments are conducive to spread of disease ○Droplet infection rate likely to be higher ○Contact infection also much higher • Dirty environments harbour pathogens ○E.g. using human sewage to fertilise crops is sometimes done in parts of the world ○This is likely to cause the spread of faecal-oral pathogen spread

HIV/AIDS

• Virus • Human immunodeficiency • Attacks and destroys immune cells weakens immune system • Open to range of opportunistic diseases • Secondary infection • Exchange of bodily fluids • Sharing of hypodermic needles • Across placenta during child birth • From mother to baby during breast feeding • Use of unsterilized surgical equipment • Worldwide • 45 million sufferers

Structure of Antibodies

•• 4 polypeptide chains held together by disulphide bridges •• Constant regions, which remains the same •• Variable region which changes •• Hinge regions, which allow for flexibility

Traditional Medicines

•• 80% of global population rely on traditional medicines ••Many modern drugs have their origins in traditional medicine

The overall, main action of antibodies is neutralisation:

•• Attach to antigen on pathogen •• Blocks binding site, preventing pathogen from binding to host cells

Inflammation

•• Attracts phagocytes •• Attracted by chemotaxis

Blood Clotting & Skin Repair

•• Body prevents excess blood loss •• Clot acts as temporary seal •• Prevents infection and first step in skin reparation •• Requires calcium ions and 12 cofactors ○○Clotting factors snaprevise.co.uk 109 •• These initiate and see through the clotting cascade •• After the clot, a scab forms, and the epidermis heals more permanently

Clonal Selection

•• Bound T-helper cells produce cytokines •• Attract B-lymphocytes •• Best fitting lymphocyte binds to the macrophage ••Occurs in lymph nodes

Inflammation

•• Caused by damaged cells •• Damaged cells release histamines ○○Cause capillaries to dilate ○○Increase tissue fluid ○○Increase flood supply ○○Increased phagocyte supply •• Damaged cells release chemokines ○○Chemicals to which cells can show chemotaxis ○○Attracts phagocytes •• Phagocytes invade the tissues ○○Carry out phagocytosis

Cell signalling

•• Cells need to communicate to work effectively •• This is achieved through release of cytokines and cell surface receptors •• Receptors must be complementary to the signaling molecule ○○T and B lymphocytes have receptors that are complementary to the foreign antigen ○○When the antigen is detected, the lymphocyte is stimulated ○○Specialist surface receptors detect chemicals signals

Clonal Expansion

•• Cytokines produced by T-helper cells cause B-lymphocytes to divide ••Multiple B-cells produced •• Rapid clonal expansion can cause mutations ○○As a result, increasingly close matches may be found •• B-cells released into the bloodstream •• Some B-cells make memory cells and are stored in glands and retained for life •• Remaining B-cells circulate in the blood plasma ••May become plasma cells, producing antibodies •• Antibodies are produced in the blood on a large scale

Antigen Recognition

•• Cytokines produced by antigens attract T-helper cell •• Thousands of different T-helper cells, which fit to different antigens •• Effectiveness of T-helper cells depends on the closeness of the bonds

Personalised Medicine

•• DNA of plants can be sequenced, allowing candidates to be identified as potential vaccinations •• In future, might be possible to sequence genomes of individuals, identify disease, and generate personalised medicine for that condition

Skin

•• Epidermis ○○Tough outer layer ○○Secretes sebum to waterproof skin ○○Keratin secreted, toughening skin ○○20-30 cells thick •• Dermis ○○20-40 x thicker than epidermis ○○Contains sensory receptors cells, capillaries and hair follicles •• Lower layers of the skin are site of cell division •• Replace cells lost from surface •• Sebaceous glands secrete lactic acid and fatty acids ○○Forms acidic environment ○○Disrupts bacterial processes

Influenza

•• Influenza is a killer disease •• Caused by a virus •• Occasionally, mutations lead to a new strain •• This may cause an epidemic ○○1918 epidemic killed 40 million ○○A large-scale outbreak is called a pandemic •• In order to prevent pandemic, vaccination occurs •• People at risk are immunized •• Strain of flu that are vaccinated against change each year •• Research is undertaken to decide which strains are most likely to spread

Mucous Membranes

•• Lining of organs involved in protection and absorption •• Present at most interfaces between body and external environment •• Secrete sticky mucus and lysosomes enzymes •• Can be lined with cilia

Natural Medicine

•• Natural diversity of plants brings hope for discovery of new medicines •• New technology has allowed scientists to chemically screen plants for potential uses as medicines •• Highlights importance of maintaining biodiversity •• E.g. the concept of probiotics - harmless bacteria which compete with harmful gut bacteria effectively treat symptoms

Modern Research

•• Nature is often used as a starting point for research •• Scientist are often able to identify and isolate the active ingredient

Phagocyte mode of action

•• Phagocyte envelopes and engulfs the pathogen •• The membrane folds inwards: phagocytosis •• Pathogen is trapped inside in vacuole called the phagosome •• Lysosome fuse with the phagosome forming phagolysosome •• Release enzymes into it, called lysins •• Lysins digest the bacterium •• Products of the digestion are entirely harmless •• Nutrients can then be absorbed into the cytoplasm or exocytosed into extracellular fluid

B Cells (B lymphocytes) can be...

•• Plasma cells ○○Circulate in blood ○○Produce and secrete antibodies into circulation •• B memory cells ○○Remain in the body for many years after the initial infection ○○Serve to 'remember' the antigen

Benefits to antibiotics

•• Prevent growth of bacteria •• Therefore prevent disease caused by bacteria

Antibodies are produced in response to infection: •• Primary Infection •• Secondary Infection

•• Primary Infection ○○When an infecting agent is first detected, it takes a few days for antibodies to be produced ○○Once pathogens have been dealt with, number of antibodies in the blood drops rapidly •• Secondary Infection ○○Antibodies do not stay in the blood ○○If the same infection occurs, antibodies must be produced again ○○This time, antibody production is much more rapid ○○Concentration of antibodies rise sooner and reaches a higher concentration

Herd immunity

•• Provide vaccination to all population at risk ••Once enough people are immune, the infection will stop spreading ••Often, only the people at greatest risk or exposure are vaccinated

Further Research

•• Receptors on viruses can be sequenced •• Drugs can then be developed to block these receptors

Coughing and Sneezing

•• Reflexes that expel pathogen trapped in mucous •• Effectively removes pathogen from airway tract

T Cells (T lymphocytes) can be...

•• T helper cells ○○Release cytokines ○○Stimulate B cell maturation ○○Promote phagocytosis •• T killer cells ○○Identify and kill infected host cells ○○Especially important during viral infections snaprevise.co.uk 112 •• T memory cells ○○Long-term immunity •• T regulator cells ○○Recognise when the pathogen has been removed and is no longer a threat ○○Alerts the rest of the immune system that it no longer needs to be active ○○Immune response ends

Ring immunity

•• Used when new cases of disease are reported •• People in the immediate vicinity of new cases are vaccinated •• Populations around infection are vaccinated, preventing the spread

Antigen Presentation

••Macrophages engulf pathogens •• Do not fully digest it •• Separate antigens •• Display antigens on their surface •• Become antigen-presenting cell (APC) •• This attract lymphocytes which can neutralize the antigens

Risks of antibiotics

••Over the years have been over-used and misused ••Misuse gives mutant bacteria the chance to populate hosts even if they are being treated with antibiotics •• Antibiotics now are less likely to give the desired result •• E.g. MRSA ○○Methicillin-resistant staphylococcus aureus ○○Requires hospitalisation and carefully monitored administration of limited-availability antibiotics ○○Can be lethal

Wildlife

••Wildlife can be observed to view self-medicating of animals: ○○Bears rub citrus oils to prevent insect bites ○○Birds line nests with medicinal leaves to protect chicks from blood sucking mites

Physical contact

○Common for skin diseases like ringworm, a fungal disease in cattle, which is spread by an infected animal brushing against an uninfected animal ○Direct transmission

Faecal-oral transmission

○E.g. E. coli ○Transmitted by consumption of food or water with traces of faeces from infected animal ○Direct transmission

Vector transmission

○E.g. malaria ○The pathogen is carried from one host to another via a vector ○With malaria the vector is female mosquitoes ○The pathogen cannot be spread directly from one host to another ○Indirect transmission Some environmental factors can

Droplet transmission

○E.g. through sneezing - pathogen is contained within mucus ○Type of direct transmission

Transmission by spores

○Spores are a resistant form of the pathogen ○They can resist extremes of temperature, pH, and even strong disinfectants ○E.g. anthrax ○Direct transmission

Antitoxins

○○Antibodies can also bind to toxins released by the pathogens, rendering them harmless

Opsonins

○○Antibodies can label the pathogens as foreign to phagocytes ○○Speeds up the process of phagocytes identifying antigens

Agglutinins

○○Large antibody can bind many pathogens together ○○Immobilises them ○○Prevents them from entering cells as they are now part of a much biggers structure ○○Aids phagocytosis

Macrophage

○○Larger cells ○○Manufactured in bone marrow ○○Tend to settle in organs, particularly lymph nodes

Neutrophils

○○Multilobed nucleus - enhances flexibility of cell ○○Manufactured in bone marrow ○○Short lived ○○Released in large numbers