Module 7: Infectious Diseases Flashcards
Causes of Infectious Disease
What is a disease?
Condition that impairs the normal functioning of an organism.
Types of pathogens?
Bacteria, Viruses, Fungi, Protists, Prions and Macroscopic Parasites
What is tuberculosis?
Caused by the bacteria Mycobacterium tuberculosis
Enters the body through infectious droplets. When macrophages try to kill the bacteria, the bacteria survives, and replicates within the macrophage, forming a hard layer of dead tissue around the infected macrophage that results in chest pain, and chronic coughing and weakness.
What are bacteria?
Prokaryotic, unicellular organisms. They cause disease by releasing toxins or damaging host tissues. For example, tuberculosis or tetanus.
What are fungi?
Eukaryotic, non photosynthetic organisms with a cell wall. Causes disease by the digestive enzymes they produce.
For example, Athletes foot or stem rust in plants.
What are protists?
Eukaryotic, unicellular microorganisms without a cell wall.
For example, malaria or phytophthora dieback in plants.
What is malaria?
Caused by the protists of the plasmodium genus, such as plasmodium falciparum.
Spread by infected female Anopheles mosquitoes
Feeds on haemoglobin, causing RBC to pop.
Symptoms include fever, muscle pain, and nausea.
The pathogen spreads to the liver cells, in which antibodies will then be produced to limit the spread of the pathogen.
What is a virus?
Non-cellular, consisting of a single nucleic acid (RNA or DNA) encased in a protein coat (capsid)
Penetrates a host cell, and uses the cell’s enzymes and nutrients to produce viral proteins and nucleic acids, which assemble new viruses to infect other cells.
For example, Influenza and COVID-19
What are prions?
Non-cellular infectious proteins, which are abnormally folded.
They convert normal proteins into abnormal structures, and usually affect brain and neural tissue, leading to neurodegeneration.
For example, Kuru is a disease caused by a prion found in contaminated human brain tissue, spread by cannibalism.
How do Pathogens establish an infection?
- Entry - This can be done through respiratory tract, gastrointestinal tract and through wounds in the skin.
- Invasion - Pathogens then spread throughout the body by infiltrating cells, travelling through bloodstream or through tissue fluids.
- Establishment - Pathogens establish themselves with the help of adhesins.
- Hiding - Pathogens evade the immune system through various means, like hiding in parts the body can’t reach like the intestines or within cells, attacking the immune system’s antibodies, T-Cells and B-cells, or covering themselves in host cell antigens.
- Exit - Once established, the pathogen will reproduce and some will leave the body to infect other hosts.
What are the methods of transmission?
Direct contact and Indirect contact
Factors that contribute to epidemics on a pathogenic level.
Virulence - effect a pathogen has on the health of host
Antibiotic resistance
Genetic shift - loss of genetic variation or selection pressures can cause a population to lose genetic resistance
Herd Immunity
What are epidemics?
When the number of people affected by a disease is higher than the endemic level in several communities. A less severe version is an outbreak, while a more severe version is a pandemic.
Factors that contribute to epidemics at a human level.
Human migration or global travel acts as vectors across the world
High human density due to poor infrastructure increases likelihood for a disease.
Lack of amenties like clean water, effective sewage systems or adequate health services
Lack of healthcare
What are Koch’s Postulates?
- Presence in infected individuals and absence in healthy ones
- Pathogen must be able to be isolated from host and grown in pure culture.
- Healthy host must develop same symptoms as the infected host once infected.
- Pathogen must be re-isolated from the second host and grown again.
What was Louis Pasteur known for?
Created Microbial fermentation theory, when he discovered lactic acid bacteria in sour wine.
Development of pasteurisation, heating liquids to 60-100 degrees to kill off microbes before cooling it.
Proved germ theory using the swan-neck flask
–> Bone broth prepared in two glass flasks, one straight neck and one swan neck.
–> Pasteurised the broths before leaving it alone for several weeks
–> Disproved the concept of spontaneous generation
Vaccination:
Pasteur injected old cultures of cholera into chickens. The chickens became ill, but then became resistant to future, fresh injections.
He realised that weakened strains of disease can help animals develop immunity.
Went on to develop vaccines for anthrax and rabies.
Fungal pathogens
Thrush
Viral pathogens
HIV
Influenza
Bacterial pathogens
Cholera
Tuberculosis
Protist pathogens
Malaria
What is virulence?
The severity or harmfulness of a disease
What is Athlete’s foot?
A fungal disease caused by a few different fungal species, one of which being Microsporum. They live on the outside layer of human skin, where they produce chemicals which break down keratin, causing itchiness, inflammation and flaky skin.
What is Influenza?
A viral disease where the virus damages lung tissue. Most symptoms are caused by the body’s own immune response, caused by the release of cytokines from infected cells. Leads to fever, cough and nasal congestion.
What are cytokines?
Cytokines are small and membrane-bound signaling cells that aid cell-to-cell communication in immune responses. They:
1. Increase activity of phagocytes
2. Help promote inflammation
3. Stimulate the production of cytotoxic T Cells
4. Stimulate B cells to differentiate to form plasma cells and memory B cells.
What are macroscopic parasites?
Multicellular pathogens that can be seen with the naked eye. Examples are tapeworm, ticks and fleas, all of which suck human blood for nutrients.
How is ebola spread?
Ebola is a viral disease that is spread through direct contact with the body fluids of an infected person.
How are indirect contact diseases spread?
Spread through intermediates, which allow the disease to spread on a larger scale.
What is an invasin?
Extracellular substance that aid pathogens in invading the host’s body. They break down host defences and facilitate the growth and spread of the pathogen.
There are spreading factors, enzymes which impact the strucutre of tissue matrices and spaces between cells.
There are clotting factors, enzymes which induce clotting, converting fibrinogen to fibrin, disguising pathogens and protecting it from phagocytes.
There are enzymes that disrupt cell membranes, facilitating pathogen entry into cells. However, some pathogens are able to bypass the cell membrane through passive entry.
Examples of adhesins
Pili and fimbriae help the pathogen stick to the glycolipids of the cell membrane.
Cell surface adhesion molecules have shapes that bind to the proteins found on the cell membrane.
How do you control an epidemic?
- Identify the pathogen
Done through clinical observation and laboratory confirmation - Environmental Management - to reduce contact with pathogen
Cleansing water supplies
Creating sanitary conditions like removing waste from public areas and building sealed sewage systems - Quarantine
What was Robert Koch known for?
- Proved Bacilus anthracis is the cause of anthrax. Done by extracting the bacterium from a sheep which had died from anthrax, grew it and injected a mouse with it, and showed that the mouse had developed the disease as well.
- His postulates
- Created advanced staining and culture techniques
Used methyl violet dye to show up the bacteria causing septicaemia, significantly helping our ability to see bacteria under a microscope. Also, by solidifying broth with gelatine and agar, Koch created a medium to culture bacteria which easier to handle than the liquids Pasteur used. - His pure culture techniques allowed him to identify the causative agents of tuberculosis and cholera, and helped the future identification of the pathogens responsible for typhus, tetanus and the plague.
What is intensification?
Intense farming, various techniques that are performed to yield greater output, such as planting crops in higher density, increasing direct contact between individuals and thus, risk of infectious disease. To combat this, farmers employ intensive use of medicine and antibiotics, yet this creates more risk as overuse of medicine can promote resistance among pathogens.
For example, in the UK 1990s, there was an outbreak of Mad Cow Disease, a fatal neurological condition in cows caused by a prion. This was due to farmers using the leftovers of previous animals, such as their cartilage, organs and bones to create food for their living farm animals. This intensification allowed farmers to save resources, yet in doing so, caused the prion causing Mad Cow Disease to spread throughout the cattle population in the UK.
Example of a disease caused by the movement of people and goods
Foot and Mouth disease - Originated from the importation of viral infected lamb from Argentina and Chile, while costed the agricultural industry over 14 billion dollars. These diseases are combatted by border control measures like intense screening and inspection processes at airports and docks.
Non-specific vs Specific immune defence?
Non-Specific (or innate defence) repels all pathogens equally. You are born with all of your non-specific defence mechanisms. Includes barriers to infection and innate immune system.
Specific defence targets specific pathogens, which develops and adapts in response to pathogens which the body encounters over time. Involves the adaptive immune system.
What are the lines of defence?
- Barriers to infection
- Innate immune system
- Adaptive immune system
What is an antigen?
A molecule capable of triggering an immune response. The body distinguises all antigens as either self antigens, or non-self, attacking the non-self antigens. Examples of self antigens are cells, proteins or chemicals made by your own body. Examples of non-self antigens are pathogens, chemicals in venom, proteins in food or transplanted organs and blood.
What are the barriers to infection?
First line of defence, which stops pathogens from entering the body, and is non-specific.
What is Innate Immune system?
Activated when the pathogen breaks through the first line of defence, attempts to stop the pathogen from establishing itself within the body and spreading.
- Phagocytosis
- Inflammation
What is the adaptive immune system?
The third line of defence, which is specific. It activates as soon as the pathogen enters the body, but takes a while to work. When a pathogen enters the body for the first time, the adaptive immune system identifies its weakness in order to remove the pathogen. Adaptive immune system creates memory cells, which allows the body to quickly recognise and respond to antigens if re-exposed.
What are all the barriers to infection?
- Physical
Physically block the pathogen from entering the body. For example, skin, mucus and cilia.
Cilia sweeps mucus containing pathogens along to respiratory tract to be coughed, sneezed or swallowed. - Chemical
Make body surfaces inhospitable for pathogens. Lysozymes are enzymes that break down the cell walls of bacteria, and is found in tears, saliva and mucus.
Acidic secretions such as toxic metabolites, are found in the ear canal, vagina and stomach and contain degradative enzymes like lysozyme. - Microbiological
Microflora are microorganisms in our body that don’t cause harm, found on mouth, skin and intestines. They compete with pathogens for space and nutrients, and produce antimicrobial chemicals, which prevent the growth of other organisms.
What is phagocytosis?
Process by which phagocytes (a type of WBC or leukocyte) engulf and destroy foregin or unwanted material. It occurs in 4 steps.
1. Phagocyte englufs foreign material, forming a phagosome
2. A lysosome fuses with the phagosome, forming a phagolysosome
3. The enzymes within the lysosome break down the foreign material.
4. Small waste fragments are expelled by exocytosis
What are natural killer cells?
Cells which are important in defence against virus-infected or cancerous cells. They release cytotoxic chemicals such as perforin, which can kill cells directly.
What is inflammation?
Accumulation of fluid, plasmid proteins and WBC at a site where tissue is damaged or infected. Characterised by redness, heat, swelling and loss of function in area.
Steps of the inflammatory response:
1. Pathogen successfully makes it through the first line of defence, or tissues are damaged.
2. Injured cells release chemokines, which attract neutrophils and make mast cells release histamine, which dilates blood vessels, and allowing antimicrobial factors to pass into the affected area.
Important: The increased temperature slows the growth and replication of pathogens in the inflamed area, as enzymes denature outside of their optimal temperature. Also, it enhances the activity of WBCs,
What is the complement system?
A set of more than 30 proteins that float around in blood, no cells. When a pathogen breaks through, the proteins rapidly bind to it, leading to a cascade of reactions on its surface. For example, it can punch holes in the cell membrane, promote inflammation, and opsonisation, meaning flagging the antigens for removal.
Types of white blood cells?
Phagocytes (ingesting unwanted material)
- Neutrophils
- Macrophages
- Mast Cells
Lymphocytes (Specialised for adaptive immune responses)
- B cells
- T cells
Differentiate between the phagocytes
Neutrophils are the most abundant, able to quickly enter tissues and engulf pathogens in acute infections. Also release antimicrobial compounds like hydrogen peroxide, disrupting bacterial and fungal cell membranes.
Macrophages live longer than other phagocytes, and thus assist in chronic infections. Play a role in activating the adaptive immune system, by acting as antigen-presenting cells. This allows T cells to recognise the antigens of the pathogens invading the body.
Dendritic cells have a similar role to macrophages.
All release cytokines, which attract other immune cells to the site and promote inflammation.
What are the two parts of adaptive immune system?
Antibody mediated immunity
Cell mediated immunity
What does the B lymphocyte do?
B cells are a type of WBC, produced in bone marrow. Once matured they are released into bloodstream, where they accumulate in the lymphoid tissues. When a B cell comes into contact with a specific antigen, it becomes activated. It begins to proliferate to form millions of clones. These daughter cells become either plasma cells or memory B cells.
Plasma cells produce antibodies, which are proteins with specific shapes that bind to antigens.
What are the antibody strategies?
Neutralisation - deactivating a pathogen or toxin by blocking its active site
Precipiation - antibodies bind to soluble antigens to form insoluble antigens, which assists in phagocytosis
Agglutination - antibodies bind to antigens on the surface of cells to form clumps of cells
Activating complement system
What are memory B cells?
Remain in lymph tissue and provide immunological memory. If an animal is re-exposed to the same antigen, memory cells recognise it and divide to produce plasma cells. Creates a faster and stronger immune response.
What is cell-mediated immunity?
Involves T cells. Produced in bone marrow but mature in the thymus gland. Once matured, they are released into the blood until they come into contact with their specific antigen. It will then proliferate into one of four types.
What are the types of T Cells?
Cytotoxic - ‘Killer’ Cells kill foreign, infected and abnormal cells, including our own body cells. To kill, they secrete or inject toxic chemcials into the target pathogen.
Helper - Help promote the activites of other immune responses, but secreting cytokines.
Suppressor - Deactivates immune system once antigen has been destroyed.
Memory - Same as B cell, and if body is re-exposed, divides into cytotoxic and helper T Cells.
What is active immunity?
Active
Occurs when immune system makes its own B cells, T cells and antibodies in response to an antigen. Natural active immunity is when you become immune after catching a disease, as the pathogen introduces the anitgen that triggers the adaptive immune system. Artifical active immunity involves vaccines, where a controlled dose of antigenic material is introduced to the body.
What is passive immunity?
When antibodies are transferred to an unimmunised person, providing them with temporary protection. Natural passive immunity involves babies who become immune due to antibodies it receives from its mother through the placenta and breast milk. Artificial passive immunity is when your body is injected with another individual’s antibodies.
What is basal resistance?
Basal Resistance - The plant immediately fortifies itself against infection by becoming impenetrable, closing the stomata of the leaves. There is also callose deposition, which limits the spread of disease between cells by blocking off access to other cells. Also releases various chemicals, such as sopoins which destroy the pathogen membrane. Phytoalexins attack the pathogens by impairing their growth.
What are the general immune defences of plants?
- Physical
Exterior barrier is a waxy cuticle made up of lignin and cutin. Many plants are also covered in bark, an exeternal layer of dead cells. Plant’s cell wall physically prevents the pathogens to penetrate the cell. Thorns, hairs and trichomes and drooping leaves deters contact with insects that may carry disease. Leaf shape prevents water from pooling, and giving rise to waterborne diseases. - Chemical
Plants possess antimicrobial chemicals, such as antibiotics. They also have toxins that target insects that feed on plants.
What is gene for gene resistance?
Concept that dictates that a plant will only succeed in resisting a pathogen if it contains a specific resistance gene against the pathogen. Simiarly, the pathogen must contain a specific avirulence gene, or in other words, not contain the virulence gene that makes it pathogenic. Only through this resistance gene can plants destroy the pathogen.
What is systemic acquired resistance?
Activated in the plant following exposure to a pathogen, where the plant is able to mount a faster and quicker attack for subsequent re-exposures.
What is the hypersensitive response?
Limits the pathogen access to just the host plant, involvinf apoptosis by the host plant to restrict the pathogen to its infected site, ands save the rest of the plant.
Factors affecting the spread of diseasse
Pathogen’s ability to:
- Survive
Dictates how far the pathogen is able to travel, and opportunity to affect.
- Growth
How quickly and easily the pathogen can replicate
- Persistence
Allows them to replicate over a long period of time. The most persistent pathogens are those that can effectively evade the immune system.
These factors affect how a pathogen is spread, whether through direct or indirect contact.
What is biomagnification?
When a certain subtance accumulates in the body tissues of organisms in increasing amounts the higher trophic level, e.g. pesticides
What is DDT pesticide?
Used to be used to prevent the spread of malaria, killing anopheles mosquitoes which act as vectors for the transmission of malaria. However, use of pesticides acts as a selection pressure on the targeted population, developing resistance to DDT, which is now no longer used for these reasons.
What are anti biotics
Drugs that help treat bacterial infections. They either kill the bacteria, or slow the growth so the immune system has a greater chance of removing them. For them to be effective, they can’t damage theh host organism, so they specifically target biological pathways and molecules that are unique to prokaryotic bacteria, such as cell wall synthesis and nucleic acid synthesis. Penicllin was the first antibiotic ever discovered, which was purified directly from a type of fungus, and prevents bacterial cell walls from developing properly by inhibiting the synthesis of peptidoglycan. This prevents the bacterial cell wall from remaining osmotically balanced, resulting in the death of the cell as water moves in.
How does vaccination work?
Vaccines contain the antigens of pathogens, which are either weakened or dead. By mimicking the disease, our body is able to develop immunity to the disease by producing memory cells.
Advantages and disadvantages of anti biotics
Pros:
They aren’t specific, they can be used to kill a wide range of bacteria.
Cons:
For this reason, they often kill bacteria that aids our body.
Antibiotic resistance, which arises through spontaneous mutation, and is often due to the failure to complete an antibiotic course, enabling resistant bacteria to survive and replicate.
What is an antiviral?
Drugs that treat viral infections. They minimise the viral load by reducing the number of viruses produced in the host. The simple structure of viruses, as they are non cellular, can make it difficult to specifically target it with medicine.
How do antivirals work?
- Preventing viruses entering host cells by binding to receptors, blocking viruses from entering the cell.
- Inhibiting enzymes which catalyse the reproduction of the viral genome.
- Blocking transcription and translation of viral proteins, which need the host cell’s ribosomes to replicate.
- Preventing the virus from leaving the cell.
- Grabbing the virus while outside the cell by targeting capsid proteins.
Pros and Cons of antivirals?
Pros:
Allow for treatment of viral infections
Cons:
Antivirals are difficult to develop, thus taking time to develop.
Some conditions also have so many viral strains that it is impossible to create a corresponding antiviral, such as the common cold, which is created by over 200 viruses.
Example of an antiviral?
Acyclovir is an antiviral that treats against herpes. It blocks the production of Herpes’ DNA polymerase, so it cannot replicate.
HIV is a type of RNA virus and retrovirus, meaning it uses reverse transcriptase to produce DNA from RNA. It also relies on integrase to integrate the retroviral DNA into the host chromosome, which is permanent.
