Infectious Disease Notes PDF

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Class of 21'. Lecture notes...

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INFECTIOUS DISEASE Outcomes A student: -

analyses and evaluates primary and secondary data and information BIO11/12-5 solves scientific problems using primary and secondary data, critical thinking skills and scientific processes BIO11/12-6 communicates scientific understanding using suitable language and terminology for a specific audience or purpose BIO11/12-7 explains non-infectious disease and disorders and a range of technologies and methods used to assist, control, prevent and treat non-infectious disease BIO12-15

Content focus - Students engage with the study of non-infectious disease and disorders, including their causes and effects on human health. They explore technologies and their uses in treating disease and -

disorders as well as the epidemiology of the non-infectious disease in populations. This module examines the practical applications of STEM. It looks at the importance of understanding the multidisciplinary nature of science applications. It also examines the physiology and engineered solutions to problems related to the management of human disorders.

Working scientifically -

In this module, students focus on collecting and processing data to analyse trends and patterns and solve problems. They also focus on communicating ideas about non-infectious disease and disorders. Students should be provided with opportunities to engage with all Working Scientifically skills throughout the course

TOPIC 1: CAUSES OF INFECTIOUS DISEASE TOPIC 2: RESPONSES TO PATHOGENS TOPIC 3: IMMUNITY TOPIC 4: PREVENTION, TREATMENT AND CONTROL TOPIC 1: CAUSES OF INFECTIOUS DISEASE

INQUIRY QUESTION - HOW ARE DISEASES TRANSMITTED?

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describe a variety of infectious diseases caused by pathogens, including microorganisms,

macroorganisms and non-cellular pathogens, and collect primary and secondary-sourced data and information relating to disease transmission, including: ➔ classifying different pathogens that cause disease in plants and animals ➔ investigating the transmission of a disease during an epidemic ➔ design and conduct a practical investigation relating to the microbial testing of water or food samples ➔ investigate modes of transmission of infectious diseases, including direct contact, indirect contact and vector transmission

Disease = any process or condition that adversely affects the normal functioning of a living thing Infectious disease = a disease caused by another organism or infective agent known as a pathogen Pathogen = any organism or infective agent that causes disease, including bacteria, viruruses, fungi, protozoa, prions, parasites Communicable disease = a disease which can be transmitted from plant to plant or animal to animal ➔ Not all infectious diseases are communicable/contagious, but all communicable diseases are infectious History - Technology improvements and developments increased understanding of ID (no understanding of cause = understanding transmission and/or prevention of disease were unknown, so diseases couldn’t be properly managed) ➔ Prior to the work of scientists such as Louis Pasteur and Robert Koch, little was known about ID ➔ Spontaneous generation (living organisms can arise from inanimate materials.e.g. -

Maggots in rotting meats) was still believed As microbiology emerged, more knowledge was gained and the ‘germ theory of disease’ was proposed, stating that many diseases are caused by microorganisms (some are NID)

Classifying pathogens

Transmission of a disease during an epidemic - Understanding of transmission methods is critical to the control of disease outbreaks - Transmission involves the carrying or transfer of a pathogen from an infected host to a noninfected organism → mode relates directly to the ability of the pathogen to survive outside a host cell -

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Many pathogens live outside the host in a state of dormancy Pathogens may exist in reservoirs, any substance or tissue that is a source of pathogen that can cause further infection, either in the environment or in living hosts ➔ E.g. Spore forming bacteria such as anthrax can exist for years in a soil reservoir where the body fluids of an infected animal have seeped into the soil Human gut can be a reservoir ➔ human may be an active carrier (not affected but can pass it onto their children) harbouring the disease in their own body, or a ➔ passive carrier, transmitting the pathogen from person to person.e.g. Unwashed contaminated hands

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Macro Parasitic infections = often several hosts in the life cycle, therefore several different modes of transmission → parasite must be transmitted between each host to reach sexual maturity, successfully completing each stage of life with multiple transmissions.e.g. Liver fluke uses humans, sheep or cattle and snails as an intermediate host to complete its life cycle

‘Chain of Infection’ (must be present for a disease to spread between organisms) - A host is susceptible to the disease -

A pathogen that is capable of causing the disease

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A mode of transmission → a way for the pathogen to get from host to host

Modes of transmission -

Pathogens that cause ID can be transmitted: ➔ Directly = pathogens pass directly from person to person

➔ Indirectly = pathogen transferred from the environment .e.g. Air, food or water to the person ➔ Vector = pathogen transmitted from person to person by being carried by another organism, the vector.e.g. The anopheles mosquito is a vector that transmits the malaria parasite or the Ross River fever virus from person to person Direct contact = transfer of the pathogen via physical contact between host and non infected organism ➔ Horizontal transmission: viral spread between organisms/individuals of the same generation, or between organisms that are not parent and child -

➔ Vertical transmission: viral spread between parent and offspring Physical contact includes touching, exposure to infected skin or bodily fluids, sexual contact, biting, direct contact to wounds, prenatal (pre birth/during pregnancy), perinatal (around the

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time of birth) Diseases caused by direct contact include skin infections such as ringworn, impetigo, HIV/AIDS, herpes

Indirect contact = transfer of the pathogen to a new host via a non living object/host - organism having no direct contact with another ➔ Infection occurs from a reservoir created by the host outside itself: a fomite, any object or -

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material that carries infectious pathogens.e.g. Surface, clothes, bedding Airborne transmission: most difficult to control.e.g. Coughing or sneezing, where droplets can travel up to 8m through the air, touching infected surfaces, contaminated food or water, unsterilized surgical equipment, vectors.e.g. Mosquitos, fleas, ticks Diseases spread include measles (infected bodily fluids/droplets), gastroenteritis (bacterium E Coli from contaminated food and water), influenza (exposure to droplets and other biological matter containing influenza virus particles)

Vector contact = type of indirect transfer of the pathogen via another organism such as arthropods, species of mosquitoes, sandflies, ticks, fleas or flies. It usually involves a bite from an arthropod that is bloodsucking and transmits the pathogen, or by animals consuming the arthropod by grooming themselves.e.g flea tapeworms in dogs - Some infected plants and fungi are sources of pathogens as vectors - These diseases represent 17% of all infectious diseases in humans -

Transmission of these diseases is influenced by a complex association of environmental and social factors.e.g. Vector diseases are most common in warm, humid conditions, where environments are most favourable for insect survival and reproduction

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Diseases include: ➔ Malaria - mosquitoes, female anopheles lay eggs in water ➔ Hendra virus - fruit bats ➔ Menangle virus - pigs ➔ Dengue fever ➔ Canine and feline heartworm

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investigate the work of Robert Koch and Louis Pasteur, to explain the causes and transmission

of infectious diseases, including: ➔ Koch’s postulates ➔ Pasteur’s experiments on microbial contamination

Koch’s Postulates - Developed the agar plate technique for growing microorganisms, and used it to culture the isolated anthrax bacillus

1.

➔ Links to germ theory as they show a microorganism grown outside the body can cause disease The same microorganism must be present in every diseased heart

2.

The microorganism must be isolated and cultured in the lab and accurately described and recorded 3. When a sample of the pure culture is inoculated into a healthy host, this host must develop the same symptoms as the original host 4. -

The microorganism must be able to be isolated from the second host and cultured and identified as the same as the original species Major breakthroughs ➔ Discovery of the bacterium responsible for tuberculosis, mycobacterium tuberculosis ➔ Bacteria responsible for causing cholera - Through microscopes, he observed small microbes → he concluded there are things that are unseen to the eye, however, can impact and harm people. Presented that cholera was transmitted through the water ➔ Mapped out infected individuals, who were mostly around the broad st pump → when it shut, the incidence of cholera decreased greatly

Pasteur’s contribution -

Discovered that microbes were responsible for spoiling foods and liquids ➔ Pasteurization process developed to kill the bacteria Swan necked flask experiments ➔ Involved using flasks that had long drawn out necks (like swans) that weren’t sealed ➔ Meat broth boiled in the flasks, and as they cooled, the air was drawn in from outside. Any microorganisms present in the air didn’t reach the broth, as they were trapped in the narrow glass neck - no bacterial/fungal growth observed ➔ Bacterial growth occurred if the curve of the flask was broken off and the contents of the flask exposed to the air, tipping a flask to allow the solution in it to reach the curve where the microorganisms were trapped resulted in bacterial growth occurring

➔ This added further evidence to discredit the theory of spontaneous generation: it supported the hypothesis that the organisms that contaminated the broth and caused it to decay must be carried in the air and not spontaneously generated Uncovered the relationship between microorganisms and disease ➔ Cause of silkworm disease: devised a test that allowed the selection of healthy eggs,

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saving the silkworm industry from potential disaster ➔ In conjunction with Koch’s work in anthrax, he determined that the animals were contracting the disease even though they had no known contact with affected animals carcasses of the animals that had died from the disease were buried in fields being grazed by healthy animals, who then would contract the disease Vaccinations = established the principle of immunity, providing an effective way to prevent ID ➔ Study of cholera: developed a way to attenuate/weaken bacteria so that when they are

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introduced into a host they can cause the body to be ready to recognise the real infection ➔ Anthrax vaccine: animals not given the vaccine died when exposed, those vaccinated survived ➔ Rabies Summary - Both contributed through fostering the increased understanding of the nature of ID -

Koch: contributed to the management strategies of disease such as anthrax, cholera ➔ Specific ID are caused by specific pathogens through his postulates Pasteur:

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➔ “Created” the science of microbiology ➔ Identified microbes as the agents responsible for spoilage during production of wine, beer, vinegar, leading to the development of pasteurization ➔ Germ theory supported by swan neck ➔ Development of vaccines - Take the bacteria, weaken it, then reintroduce it as a vaccine susceptible in the human ●

assess the causes and effects of diseases on agricultural production, including but not limited

to: ➔ Plant diseases ➔ Animal diseases

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Compare the adaptations of different pathogens that facilitate their entry into and transmission between hosts

Causing disease -

For a pathogen to successfully establish an infection or an organism to cause disease, it must:

1.

Enter the host

2.

Multiply in the host tissues

3.

Resist or NOT stimulate the host defence mechanism

4.

Damage the host

Adaptations -

Pathogens have developed an array of strategies to enable them to adhere to and gain entry and persist in their hosts

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These strategis form part of the virulence factors for that pathogen. Each pathogen has a ‘toolkit’ or virulence factors that help it successfully establish itself in host tissues

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It is thought that the evolutionary strategies of pathogens are just slightly ahead of the development of host resistance strategies. The two have evolved more or less side by side throughout the history of life

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These adaptations can either: ➔ Facilitate adhesion and invasion of host by pathogens - some pathogens are cellular, so the cells must be invaded and/or with the body; all viruses must get into a cell before it can replicate ➔ Facilitate transmission between hosts - mosquitos with malaria do both of these

Examples for transmission -

Reservoirs = sites (living or nonliving) where pathogens lay dormant for long periods of time ➔ Animals ➔ Zoonotic diseases allow for greater transmission ➔ Some bacteria and viruses have the ability to resist drying out (influenza) or resist desiccation (soil borne bacteria and fungi)

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Vectors = malaria, dengue fever from mosquitos

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Rapid species evolution - high rates of mutation within the genomes of pathogens, coupled with fast reproduction rates allow pathogenic species (often viruses) to evolve at a rapid rate ➔ This means that they are more able to invade hosts and remain undetected by their immune system

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Ability to be airborne, survive in and infect water

Examples for adhesion and invasion -

Prions may ‘piggyback’ on other protein (e.g. meat) to facilitate movement through the gut, then the bloodstream, leading to infection in the brain

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Viruses must enter the nucleus of a host cell to replicate their viral genome (DNA), as they have viral surface proteins which adhere to host cell surface receptors and then stimulate endocytosis

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Some bacteria have capsules which can resist phagocytosis by host cells

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Fungi thermotolerance, containing heat shock proteins that are synthesised to cope with higher temps.e.g. Body temp. The cell wall and capsules protect the fungi from host attacks

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Macroparasite hookworms

➔ Secrete proteins that reduce host cell responses. Their third larval stage allows them to travel through soil and invade the hair follicles migrating through circulation to lungs, trachea and intestines ➔ Teeth enable the worm to anchor to the gut lining Adaptations of pathogens Adaptation of pathogen

Explanation

What does it facilitate Invasion or transmission or both

Example/s of organism

Complex life cycle

Some species of pathogens have more than one host and a complex or indirect life cycle. Pathogens with a complex life cycle use aspects of their host’s way of life to aid transmission and entry into the next host.

Both

Pathogens can cross skin barriers by being in the saliva of a biting insect such as dengue fever caused by dengue viruses carried in the bite of an aedes mosquito

Highly specialised mouthparts are inserted into host skin to attach. They absorb the nutrients digested by the host but can’t be released through normal defecation. They release thousands of fertilised eggs which leave the host in the faceses to be spread to other people

Invasion

Hocks/suckers

Biologically active molecules are secreted in saliva to prevent vasoconstriction and prevent host from forming a clot or

Malaria caused by plasmodium carried in the bite of an anopheles mosquito Parasitic flatworms such as tapeworms have complex life cycles with adaptations for each stage and host → in the final host tapeworms have hooks or suckers on their scolex that help attach the worm to the lining of the host intestine

initiating an inflammatory response → ticks Immunomodulatory proteins that reduce host cell immune responses can be secreted → hookworms Attachment structures

Many pathogens need to attach to a cell before entry and colonisation.

Invasion

Adhesion structures include fimbriae and pili → fimbriae are

Bacteria have adhesions, proteins or protein complexes that help them bind to the surface of the potential host cell Helicobactor pylori causes stomach ulcers, producing a group of adhesions that help it attach to the stomach lining

usually thinner, shorter, less rigid and more numerous than pili, specialised for attachment → pili are involved in attachment and gene transfer in bacterial conjugation Phagocytosis Part of the immune system that kills pathogens Some pathogens go into cells to avoid phagocytosis using endocytosis Some fungi and bacteria has a special membrane capsules that is a barrier from

Intracellular pathogens

Invasion

Bacteria are larger than

including all viruses,

viruses and are usually

need to enter the host

taken up by

cell for growth and

macrophages in

reproduction. Being

phagocytosis →

inside a host cell is

mycobacterium tuberculosis is taken up by alveolar macrophages and causes tuberculosis

advantageous as it avoids direct contact with antibodies and phagocytes (host immune response) →

the white blood cells from reaching them

process by which cells internalise solid matter including microbial pathogens ‘cell eating’

Endocytosis

Being smaller than

Invasion

bacteria many viruses enter a host cell by

Influenza A HA protein of influenza A virus binds with host surface receptors and

binding to the

adenoviruses that

membrane receptors on

cause respiratory

the host cell, triggering

diseases such as the

endocytosis. In receptor

common cold,

mediated endocytosis

bronchitis and

the pathogen is

pneumonia → breaks

enclosed in a vesicle

down the endosomal

and taken into the cell

membrane so the virus

→ process of actively

can enter the cytosol to

transporting molecules

move into the nucleus

into the cell by engulfing it with its

HIV

membrane Some protozoa have microtubules that protrude into a host cell and facilitate entry into host cells Resistant structures

Helps them to exist outside the host. Outside a host cell a virus is a virion which is a complete, infective form of the virus consisting of a capsid (protein coat) around the genome which can be RNA or DNA. The virulence of the virion depends on its adaptive

Both HIV and smallpox transmission

Some bacteria...