Year 12 Biology Module 7 Infectious Diseases PDF

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HSC Module 7 : Infectious Diseases Causes of Infectious Disease Inquiry question : How are diseases transmitted? ● Describe a variety of infectious diseases caused by pathogens, including microorganisms, macroorganisms and non-cellular pathogens, and disease transmission ⇢ An infectious disease is caused by an infective agent, pathogen ⇢ The likelihood of an organism developing an infectious disease depends on the pathogenicity and host defence capabilities. ⇢ Factors affecting the development of infectious diseases in organisms are Host, Environment and Pathogen. MICROSCOPIC ORGANISMS Classification of different pathogens Classification

Features

Transmission

Examples

Cellular (living) Protozoans

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Unicellular eukaryotes Reproduce asexually, binary fission

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Can be transmitted through water consumption Vector transmitted e.g flies

Malaria

Fungi (Eukaryote)

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Eukaryotes Cell wall made of chitin Fluffy appearance due to hyphae, spreading to form mycelium structures

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Secrete digestive enzymes which break down organic matter

Tinea

Bacteria (Prokaryote)

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Prokaryotes Exists almost everywhere Some lack cell wall and therefore are obligate intracellular parasites

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Vector transmitted e.g soil, plants, water Contact with contaminated objects

Leprosy

Non-Cellular (non-living)

Virus

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Requires host cells to reproduce and use the reproductive mechanisms of the host to replicate -

Are a piece of genetic material cased in a capsid Viruses that infect bacteria are bacteriophages

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Can infect all kinds of organisms Attachment Penetration Uncoating

HIV/AIDs

Prion

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Smallest agents of disease Comprised of solely protein

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Promoting abnormal folding of proteins in the human nervous system

CJD - a neurodegenerative disease- misfolded proteins form in the brain

MACROSCOPIC ORGANISMS Classification of different pathogens Example

Features

Endoparasites Helminth

Transmission Live inside the body

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Endoparasitic worms that live and feed on a live host

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Ectoparasites Flea/Mosquito

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Examples

Reside in intestinal tract and prevent the host from absorbing nutrients properly Inhibit immune system

Intestinal Worms

Live outside the body -

Live outside the body usually sucking blood

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Inject toxins causing partial paralysis, inflammation or allergic reactions

Ticks, Nits

Investigate modes of transmission of infectious diseases, including direct contact, indirect contact and vector transmission

Modes of transmission

Description

Direct Contact

Occurs when there is physical contact between the host and a non-infected organism. - Horizontal transmission : not family - Vertical transmission : family (i.e. mother to baby during childbirth) E.g. touching, sexual contact, kissing

Indirect Contact

Occurs when the host and another organism have no direct contact with each other, usually from a reservoir created by the host outside itself, such as contaminated materials and surfaces or objects. E.g. coughing or sneezing, touching infected surface, contaminated food/water

Vector Transmission

Occurs through arthropods such as certain species of mosquitoes, sandflies, ticks , fleas and flies, or through aquatic snails. E.g. getting bit, animals eating the arthropod through grooming

Investigate the work of Robert Koch and Louis Pasteur, to explain the causes and transmission of infectious diseases Koch’s postulates It is a set of criteria that must be met in order for a particular microorganism to be identified as the cause of a particular disease. 1. The same microorganism must be present in every host presenting with a specific disease with specific symptoms. 2. The same microorganism must be isolated and cultured in a laboratory, and accurately described and recorded. 3. When a sample of the pure culture is inoculated into a healthy host*, the host must develop the same symptoms as the original host. 4. The same microorganism must be able to be isolated from the second host, and cultured and identified as the same original species. Limitations : - Some pathogens are able to colonise in healthy hosts, not only infected hosts - Koch’s postulates did not take into account asymptomatic carriers, whereby some infected individuals do not display symptoms of the disease but are still carriers of disease. - Viruses are not able to be cultivated in cell culture, do not meet postulates 2 and 3 - i.e. viruses need a host cell to replicate, cannot proliferate on their own - Diseases with multiple pathogens working in unison may not be identified with Koch’s postulates ●

Pasteur’s experiments on microbial contamination ➔ Swan-neck flask experiment demonstrated that bacteria and mould cannot generate spontaneously ➔ The curve of the flask prevents outside air from entering the flask, no contamination occurs. ➔ When the neck of the flask is broken off, bacteria reaches the sterile broth and organism growth occurs. ● Assess the causes and effects of diseases on agricultural production Australia is geographically isolated, allowing it to be free from many infectious diseases that affect other plants and animals in other countries - Stringent biosecurity controls reduce the likelihood of disease transmission from pathogens

Causes of infectious disease in agricultural organisms: ➔ Pathogen : availability, transferral capabilities, increased virulence factors such as adhesion to and invasion of tissues ➔ Environment : overcrowding, lack of sanitation and build up of wastes, reservoirs for pathogens to thrive ➔ Host : compromised immunity, species susceptibility, poor nutrition, drought

Effect of infectious disease in agricultural organisms: ➔ Devastate the agricultural industry ➔ Loss of produce for self sustainability ➔ Value of exports will decrease ➔ Possibility of diseases transferring to humans

Animals and Plant Diseases Endemic Diseases

Exotic Diseases

Disease that are consistently present in a country E.g. Anthrax (Sheep & Cattle), Footrot (Sheep)

Introduced disease E.g. Foot and Mouth Disease

E.g. Footrot (Sheep) Pathogen : Dichelobacter Nodosus Environment : Bacterium will only survive in soil outside the host for max. 4 days. Long, dense and wet pastures aid in pathogen survival and transfer. Warm weather is also favourable for bacterial growth. Host : Overgrown hooves provide a suitable environment for the bacteria. Dermatitis between the toes must already be present for the bacteria to invade and establish an infection.

Compare the adaptations of different pathogens that facilitate their entry into and transmission between hosts ⇢ Pathogens may possess adaptations to penetrate defence barriers of plant and animal hosts, enhance transmission and spread of disease. ●

Pathogen Fungi

Adaptation -

Mucous membranes and chemical barriers

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Developed a more complex and sophisticated mechanism to penetrate the structural defences (cuticle layer, bark, or lignin) of plants. Use of appressorium to attach to plant surfaces with extracellular adhesives Hydrolytic enzymes help split molecules using water, break bonds between proteins, nucleic acids, starch and other macromolecules. Mucus contains antibodies that bind to pathogens and prevent them from invading. E.g Helicobacter pylori. has a special flagella to help move through the mucus lining of the stomach → uses chemotaxis to bind to epithelial cells → change the pH of the micro environment directly surrounding the bacterial cell by releasing urease to convert urea to ammonia (can only survive between pH 4 and 8.2) → allowing for survival of cell in mucus lining of stomach

Vector

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Antigenic Variation

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Use of vectors to overcome skin barriers Outer layer of skin is impenetrable unless broken, even then blood clotting quickly occurs for protection Pathogens use biting insects as vectors to penetrate the skin. E.g Malaria (mosquito) and Bubonic Plague (rodents) Antigens are molecules present on pathogens that induce an immune response from host Host is able to recognise pathogen from its antigen and created targeted antibodies to fight the specific pathogen Some pathogens are able to change their antigens so host does not recognise upon secondary exposure and gives pathogen more time to colonise its host → antigenic variation E.g Flu virus are constantly circulating in many species of animals and evolving to produce new antigens → seasonal flu causes new variants → new strains evolve from genetic mixing → occurs when 2 or more different viruses attack at the same time → resulting in new assortments of surface antigens → new strains more virulent and unrecognisable to a host previously infected with a different influenza strain.

Responses to Pathogens Inquiry question : How does a plant or animal respond to infection? ● Investigate the response of a named Australian plant to a named pathogen – fungal pathogens – viral pathogens ` Passive Defences → Embedded in the plant’s physiology and are non-specific Physical

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All these substances are composed of lignin, cutin, and other macromolecules which inhibit the entrance of many pathogens and protect the plant - Cell walls and thick cuticle - Small Stomata - Bark - Vertically hanging leaves

Chemical

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Glucosides and saponins can prevent fungal and bacterial growth and are soap-like in nature Some plants produce enzymes to breakdown pathogenic toxins

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Active Defences → Activated once pathogen is recognised and non-specific Pathogen Recognition Activated once passive defences are breached.

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Physical and chemical recognition of pathogen - Cell wall fragments of fungal/bacterial cells recognised by plant cells - PAMPS recognised by chemical receptors on plant cells.

Rapid Active Response Purpose to seal wounds and kill pathogens quickly

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Pathogen recognition triggers cell membrane permeability Certain ions (calcium) flood into cell and trigger cell responses by activating expressions of genes - Oxidative Burst :H20 release to kill microbes directly - Cell Wall Apposition : Materials from cytoplasm aggregate to reinforce cell wall at the site of defects - Apoptosis : Programmed cell death.

Delayed Active Response Limit the spread of pathogens

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Repair wounds in bark using gum secretion Release of lysozyme-like chemicals Release of salicylic acid plays a role in plant ‘memory’ of pathogens and sends messages throughout the entire plant. Release of chemical messengers is part of a plant’s SAR, signalling for uninfected cells to protect themselves.

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Analyse responses to the presence of pathogens by assessing the physical and chemical changes that occur in the host animals cells and tissues Body defences/Immune systems

Innate (inherited and non-specific) Genetically preprogrammed, with repeated exposure to the same pathogen, the body responds in exactly the same way.

Adaptive (acquired and specific) It is the next line of defense, it swings into action when the innate immune response fails to clear the pathogen from the body.

First Line - physical and chemical barriers formed by tissues ➔ Physical : skin, cilia, gut microbiome ➔ Chemical : tears, stomach acid, mucus ➔ Biological : urine flow, sphincters, peristalsis

Third Line - Immune response: chemical responses by cells ➔ Lymphocytes ➔ Antibodies ➔ Memory cells: - B cells (Humoral) - T cells (Cell-mediated))

Second Line - inflammation: physical and chemical responses of cells ➔ Phagocytosis ➔ Inflammation ➔ Fever

Phagocytes Neutrophil -

Quick First responders Clear stuff out

Macrophage -

Macrophage = big + to eat They consume more than other phagocytes

Dendritic Cell -

APC after phagocytosis Link between the 2nd and 3rd line of defence (assist in gaining memory)

Phagocytosis ⇢ Uses chemicals such as hydrogen peroxide, superoxide and nitric oxide, to destroy and digest the pathogen. Then releases the degraded products. Inflammation (Localised response to infection) 5 cardinal signs of inflammation : pain, heat, redness, swelling, loss of function 1. Bacteria and other pathogens enter wound 2. Platelets from blood release blood clotting proteins at wound site 3. Mast cells secrete factors that mediate vasodilation and vascular constriction. Delivery of blood, plasma and cells to the injured area increases. 4. Neutrophils secrete factors that kill and degrade pathogens 5. Neutrophils and macrophages remove pathogens by phagocytosis

6. Macrophages secrete hormones called cytokines that attract the immune system cells to the site and activate cells involved in tissue repair. Fever (pyrexia) ⇢ A chemical response to pathogens in second line of defence ⇢ Cytokines are chemical messengers produced by the immune response during an infection ⇢ Pyrogens (types of cytokines) trigger fever by altering the set point of body temperature ⇢ The normal body temperature for humans is 37 degrees and is controlled by the hypothalamus in the brain ⇢ Purpose is to kill or limit the growth of pathogen and enhances the activity of white blood cells, therefore strengthen the immune response Complement System ⇢ Enhances (complements) the immune defence mechanisms and provides circulating innate immunity. ⇢ Involves around 20 enzymes made in liver that circulate in the blood and extracellular fluid ⇢ Activate a chain of biochemical reactions e.g chain of enzymes facilitated reactions

Immunity Inquiry question : How does the human immune system respond to exposure to a pathogen? ● Investigate and model the innate and adaptive immune systems in the human body Ms Merkulof’s play on google classroom ● Explain how the immune system responds after primary exposure to a pathogen Acquired Immunity (specific) - Primary immune response involves the first activation of the 3rd line of defence and subsequent response by T and B cells - Secondary response involves the second exposure to a pathogen

Lymphatic System - Plays an important role in the 2nd line of defence - Lymphocytes are produced by the lymphatic system and in the lymph nodes. - Swollen lymph nodes are a good indicator of how the body is responding. - During infections, pathogens enter lymph nodes (via lymph fluid) and spleen where they are filtered out, before the fluid continues on its journey

Humoral response : effective against pathogens in body fluids - Involves B cells ⇢ attacks pathogens outside cells - Involves antibodies The cells responsible for generating the adaptive immune response are known as B and T lymphocytes. B Lymphocyte (B cell) ➔

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T Lymphocyte (T cell)

Some B cells develop into plasma cells, which produce antibodies against pathogens Antibodies are protein molecules with a specific molecular structure that helps them to recognise and bind to a specific pathogen. Known as humoral response Humoral response occurs in the blood and tissue fluids of the body

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T cells transform into cytotoxic cells a.k.a killer T cells. They seek out infected body cells They bind to them and destroy them Known as a cell-mediated response

Cell-mediated response : is effective against intracellular pathogens - Involves T cells ⇢ attacks invaders inside cells - Mediated by TCRs to make direct contact with infected cells - Recognise fragments of antigens only → presented on cell surface and proteins called MHC T-cells Type

Function

Helper T cells

Release chemicals to activate the cloning of cytotoxic T cells

Cytotoxic T cells

Moves to the site of infection and release chemicals to destroy infected cells

Memory T cells

Remain in the body to respond to future infections by the same antigens

Suppressor T cells

Suppress the immune response when the infection has been defeated.

Adaptive Immune System Specificity ⇢ Antigens can be found on the membrane surfaces of pathogens, which stimulates the production of antibodies ⇢Antigens have epitopes, that are recognisable by complementary antigen receptors on B and T cells of the immune system, or by free antibodies in the extracellular fluid ⇢ Antibodies are Y shaped molecules made of 4 chains (2 larger, heavier and 2 smaller, lighter) ⇢ Antibodies have 2 binding sites, each specific to a specific antigen ⇢When they bind, an antigen-antibody complex is formed. 1. 2. 3. 4. 5.

Antigen binds to B cell via antibody Helper T cells also bound to antigen B cells proliferate and form plasma cells Plasma cells make antibodies, which circulate through blood/fluid to find antigens to bind to B cells produce memory cells.

Ways antibodies can neutralise a pathogen

Prevention, Treatment and Control Inquiry question : How can the spread of infectious diseases be controlled? ● Investigate and analyse the wide range of interrelated factors involved in limiting local, regional and global spread of a named infectious disease ⇢ Prevention is the range of measures that aim to reduce the risks of pathogens or stop infections in the first place ⇢ Treatment helps to cure diseases. They depend on factors such as pathogen type, virulence, incubation period and drugs available. ⇢ Control are procedures employed to contain and stop the spread of the disease. Ways to target and control the spread of a disease Local

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Global

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Immunisation to create herd immunity within local populations Personal hygiene practices, including washing and drying hands regularly, covering coughs and sneezes, and cleaning cleaning surfaces regularly Safe health practices, including limiting the spread of sexually transmitted infections by the use of physical contraceptives, and staying at home when you are sick Provision of public health information to improve public knowledge of diseases and prevention. Consideration of environmental conditions: - Water supply - Sanitation facilities - Food - Climate : e.g. mosquitoes which spread malaria breed in warm, humid climates - Flooding : lead to sewage overflow and water contamination on a large scale Improving swift identification: - Continued surveillance : systemic collection, analysis, interpretation and dissemination of health data - Rapid recognition of presence : disease awareness and reporting from the community, reliant on public health programs and dissemination of information - Efficient diagnosis of microbial cause : cornerstone of effective control and prevention efforts, improved by dispersion of technological advancements Appropriate and efficient responses, including isolation, treatment, identification of high-risk groups, and the provision of supplies to prevent further transmission. Communication between countries and with global health organisations is essential Implementation of quarantine measures, which involves things like travel bans in countries that are significantly affected by disease ...