1.6-2.8 INFECTIOUS DISEASES

Term 2

Pathogenicity

Whether a pathogen can infect a host cell (e.g. yes or no or is capable of causing disease, non pathogenic & pathogenic). Qualitative measure.

Virulence

Severity of the disease and symptoms caused by a pathogen. Quantitative measure (e.g. some pathogens can be highly contagious but have low virulence).

What are the entry points into the respiratory tract?

Nose, throat, and lungs. Enter through inhalation of airborne pathogens.

What parts of the body can pathogens infect via the gastrointestinal tract?

Stomach and intestines. Enter through contaminated food/water.

What are the entry points into the urogenital tract?

Urethra or genital openings. Often during sexual contact or due to improper hygiene.

How does recognition occur between host cells and pathogens?

Pathogens express PAMPs (type of antigen - pathogen-associated molecular patterns), not found in host cells. Host cells, especially immune system cells have specialised receptors that recognise PAMPs as foreign, triggering an immune response.

A form of molecular recognition.

What are Adhesins?

Bacterial adaptations - Surface proteins that help bacteria stick firmly to host cells.

What are Pili and Fimbriae?

Bacterial adaptations - Hair-like structures that enable adherence to host tissues and prevent removal (e.g. urinary tract).

What are Capsules?

Bacterial adaptations - Protective outer layers that shield bacteria from toxins/phagocytosis by immune cells by hiding pathogenic markers.

Think of it like a stealth cloak! Because the capsule hides the surface markers of the pathogen, it is more difficult for the immune system to recognize and target the pathogen for destruction.

What are Flagella?

Bacterial adaptations - Tail-like structures that assist bacterial movement, especially through mucosal surfaces.

What is Biofilm Formation?

Bacteria adaptations - Communities of bacteria that stick to surfaces and secrete a slimy protective layer, enhancing resistance to antibiotics and immune responses. Contributing to chronic infection (e.g. dental plaque)

Made of polysaccharides and proteins

What are bacterial Toxins?

Biochemical and Genetic Bacterial adaptations - Molecules that damage host cells and weaken immune defences. Some kill immune cells, allowing infection to persist.

What is Antigen Variation in bacteria?

Biochemical and Genetic Bacterial adaptations - Genetic mutations that alter surface proteins, allowing bacteria to avoid immune detection.

What are Antibiotic Resistance Mechanisms?

Biochemical and Genetic Bacterial Adaptations - The ability of bacteria to resist antibiotics due to mutations, which they can pass on to offspring.

What is Genome Integration for viral adaptation?

Viruses (e.g. HIV) insert their DNA into the host’s genome, avoiding detection and ensuring long-term presence.

What is Immune Evasion Proteins for viral adaptation?

Viruses produce proteins that block immune responses, helping them hide from the host’s defenses.

What is Latency for viral adaptation?

Viruses stay dormant in host cells, reactivating when conditions are more favorable.

What are Host Exit Mechanisms for viral adaptation?

Viruses spread through coughing or sneezing, allowing them to infect new hosts efficiently.

What is Hijacking Host Machinery for viral adaptation?

Viruses use the host’s cellular systems to replicate and produce proteins, saving energy and resources.

What is Antigenic Drift?

Small gradual changes in a virus which alter surface proteins to help escape immune detection.

What is Antigenic Shift?

2 viruses combine and create a new virus with different antigens, creating a new strain humans may not be immune to.

What is Using a Vector?

Enter bloodstream by using host to assist (e.g. Plasmodium parasite using mosquito vectors to enter a host's bloodstream). Certain insects have adapted to become carriers, they survive while carrying the pathogen.

How is skin a portal of entry?

Strong barrier but well-adapted pathogens may enter. Through cuts, direct penetration, insect bites, wounds.

Why do some pathogens create spores?

Bacteria, protist, and fungi produce dormant spores. Allows them to persist in harsh conditions. Then reactivate in favourable conditions. (e.g. Phytophthora cinnamomi spores make it hard to eliminate, causing root rot a serious plant disease).

How do some viruses cause infection?

They can attach, enter and colonise the host cell. Using specific molecules to recognise and bind to the host cell receptors. (e.g. influenza and SARS-CoV-2, covid-19, use spike proteins to bind to a specific receptor on host cells. Then enter and cause infection).

Why do some pathogens enter cells to survive and reproduce?

Intracellular environment provides protection from external immune defences. Access to nutrients or cell machinery necessary for replication. (e.g. Mycobacterium Tuberculosis infects macrophages, immune system cells, plasmodium parasite)

What are examples of pathogen adaptations?

Avoiding immune detection, by hiding in host cells, producing capsules to resist phagocytosis, mimic host molecules to appear less foreign.

Disable/manipulate hosts immune response to allow survival and spread.

Entry with specialised structures to attach to host cells (e.g. pili, adhesins), others enter thru wounds or inject proteins to penetrate tissue.

Producing toxins, affects the immune defence, helping them survive. Ability to survive within white blood cells, responsible for protecting the body from infection.

What is molecular recognition and what are the factors that influence it?

Moelcules (e.g. proteins) interact and bind to specific target molecules with high precision. Crucial for immune responses, enzyme activity, and cellular communication.

Factors:

-shape

-charges

-chemical properties

Describe self/non-self recognition.

The body’s ability to recognise its own cells and foreign substances. Antigens - Unique protein or carbohydrate molecules on 'non-self' substances that trigger an immune response (e.g. dust and pollen grains can be antigens triggering an immune response - allergies)

What are enzymes in terms of biochemical and genetic adaptations of bacteria?

Bacteria produce and secrete enzymes which help break down host connective tissue or survive in a hostile environment.

What are iron acquisition systems in Bacteria?

Developed compounds to capture iron from host, essential for bacteria growth.

Why do some bacteria prefer intracellular survival?

Invade/replicate in host cell helps avoid external immune responses.

What are host exit mechanisms?

Enables infection to spread via contaminated water (e.g. induces symptoms like diarrhoea) CHOLERA

What are enveloped structures in terms of Viral adaptations?

Derived from host cell - helps virus blend in and exit without triggering an immune response.

What is rapid replication for viruses?

Viral adaptation - High replication rates overwhelm and exhaust the immune system before an effective response can be mounted.

What is receptor mimicry in viruses?

Viral adaptation - Evolve to mimic host molecules, tricks host the cells into allowing them entry.

What are methods to control or kill vectors?

Eliminate/reduce breeding grounds (e.g. still and stagnant water for mozzie reproduction)

Cleaning practices (e.g. proper waste management/rubbish disposal)

Correct food storage

Barriers/traps:

-Insect repellent

-Window screens

-Insecticides

What biological methods to control or eliminate vectors?

Genetic manipulation - interferes with reproduction

Introduction of the vector’s predators

How to eliminate/slow the spread of pathogens?

Antibiotics

Antiseptics

Disinfectants

Quarantine

What is an antibiotic?

Drug used to treat infections caused by bacteria/some microorganisms NOT VIRUSES

Targets diff areas of bacteria cell

Stops production of new cell wall

Punches hole in cell wall

Stops protein production

Interferes with cell replication

What is an antiseptic?

Chemicals that kill microbes on the outside of the body (e.g. alcohol key ingredient in hand sanitiser)

What is a disinfectant?

Chemicals that kill microbes on surfaces (e.g. floors etc.)

May work to oxidise (breaking down cell membrane) or split open (disrupting the cell structure) bacteria.

How does quarantine work?

Separate the infected people from the healthy population to help prevent the spread of disease.

What is herd immunity?

When a large % of the population are immune to a disease.

How do vaccination programs protect those who aren’t vaccinated as well?

Vaccines protect unvaccinated people through herd immunity. When a large percentage of a population is vaccinated, it reduces the disease transmission, effectively creating a "shield" that protects those who cannot be vaccinated (like infants/individuals with certain health conditions/or those who chose not to get it). 

Define the term disease?

An abnormal condition of an organism’s function, typically associated with specific symptoms and signs.

What is a non-infectious disease?

Caused by many environmental/genetic factors (e.g. smoking may cause lung cancer). Cannot be spread between ppl.

What is an infectious disease?

A disease caused by a pathogen.

Define pathogen.

A disease causing microorganism.

Name 4 types of microorganisms.

Bacteria

Protists

Viruses

Archaea

What is an epidemic?

A located cluster of disease cases.

What is a pandemic?

A worldwide epidemic.

Define an endemic?

Constant rate of infection within a certain population.

What could be causes of an epidemic?

Genetic changes/mutations that increase the virulence of the pathogen.

Transmission of pathogen to new group that was previously not exposed.

Transmission of pathogens from animals to humans that hasn’t previously happened.

Low immunity/natural defence to a pathogen in the population.

What are factors that influence the spread of an infectious disease?

Transmission methods

Mobility of populations

Use, misuse and abuse of IV drugs

Spread from animals

Poor sanitation

What do pathogen characteristics determine?

The spread of the disease

Change in virulence/genetic structure.

What is drug resistance in bacteria?

Antibiotic resistance

Superbugs that are resistant to most antibiotics due to adaptations/mutations.

What are 6 examples of a pathogen?

Fungi - Tinea - Athlete’s foot

Bacteria - Salmonella bacteria - Salmonella

Virus - Influenza - Flu

Parasite - Tapeworm

Prions - Creutzfeldt-Jakob disease (CJD)

Protists - Giardia - Gastroenteritis

How do pathogens cause infection?

Cross the protective barriers of the host

Multiply inside the host

Avoid the host’s immune defences

How can bacteria damage host tissue?

By inhibiting protein synthesis

Damaging membranes which affects cellular transport

and consequently interferes with nerve function

How are fungi categorised?

Enter thru the digestive/respiratory tract

Where they grow reproduce:

-On surface of the host

-Superficial layers of the host (e.g. skin and nails)

-Subcutaneous tissues (e.g. inner skin layers)

-Inside the host (e.g. infecting inner tissues and organs)

Where are protists mainly found?

In water (e.g. rivers and seas) and soil

Mainly spread thru contaminated water

Except malaria spread by mosquito vector

Where are they mainly found in the body?

Intestinal

Urogenital

Blood

Tissue

Describe parasitic worms?

Infect host

Feed on host’s food in intestines

Lack digestive system but have highly developed reproductive system

Lay copious egg quantities that are passed out thru faeces

What are prions?

An abnormal, misfolded protein

Converts normal proteins into abnormally shaped proteins

Proteins are chains of amino acids with a specific 3D shape that is crucial for its function

Can be characterised by lesions in the cortex

What are human uses of microorganisms? Why are microorganisms important to humans?

Fermentation- Alcohol

Yeast- Baking

Probiotics- Gut microbiome

Medical technology- recombinant DNA tech

Carbon cycle

Phosphorus cycle

Oxygen from phytoplankton

What does dormant mean?

A state of reduced metabolic activity and increased resistance, allowing them to survive unfavourable conditions. No reproduction, less energy consumption etc.

Explain the key differences between bacteria and viruses.

Virus not alive NOT CELLS

Bacteria bigger

Viruses require a host to reproduce whereas bacteria binary fission

What are fungi?

Eukaryotic (uni e.g. yeast/multicellular e.g. mushrooms)

Microscopic multicellular (e.g. moulds and mildew)

Contain cell wall (usually composed of chitin)

Feed on dead, decaying matter (decomposers - heterotrophs)

Reproduce through release of spores which grow if the environment they land on is suitable.

Mycoses (plural of mycosis) - fungal infection

What are protists?

Eukaryotic (anything that isn’t classified as fungi, plant or animal).

Many are unicellular but some multicellular

Autotrophs or heterotrophs

(e.g. malaria is caused by protists often found in water)

Examples: protozoa (unicellular, animal-like by movement/predation heterotrophic ingest other microorganisms/organic matter thru endocytosis), algae (autotrophic), slime moulds (heterotrophs)

What are archaea?

Prokaryotic (unicellular)

Similar to bacteria but chemically distinct lipid cell wall allows them to survive in extreme environmental conditions

Assist in digestion

Autotroph/heterotroph

Reproduces asexually - binary fission, budding, fragmentation