Bacteria
What are bacteria?
Single-celled organisms that lack a nucleus (prokaryotes).
What are viruses?
non-cellular, tiny infectious agent made up of genetic material (either DNA or RNA) enclosed in a protein coat called a capsid.
Viruses cannot reproduce or carry out metabolic processes on their own — they must infect a living host cell and use that cell’s machinery to replicate.
What types of disease do fungi most commonly cause in humans? Name 1.
Fungal skin infections.
e.g. ringworm
What are parasites?
Organisms that live on or inside another organism (the host) and benefit by obtaining nutrients at the host’s expense.
What is direct transmission?
The spread of pathogens through direct physical contact between an infected person and a susceptible person.
What is indirect transmission?
When pathogens are spread via an intermediate object, organism, or environment, rather than direct contact between people.
What is the simplest and most effective hygiene practice to prevent the spread of many infectious diseases?
Hand-washing
True or False: All bacteria cause disease.
False. Most bacteria are harmless. Some are even beneficial.
Are viruses considered living organisms? Why or why not?
No, because they cannot reproduce or carry out metabolism on their own; they need a host cell.
What is the term for unicellular fungi?
Yeasts
What are ectoparasites? Name 3.
Parasites that are found on the surface of the body.
Mosquitoes, fleas, leeches, ticks, mites, head or body louse, bedbugs, botflies, lamprey
What are the two types of direct transmission?
Physical contact: Transmission of an infective agent through touch, kissing, sexual contact, or contact with broken skin.
Droplet Spread: via sneezing, coughing, talking (large droplets).
What are the four types of indirect transmission?
Airborne Transmission: Very small droplets (aerosols) or particles that stay suspended in the air and travel long distances. Can be inhaled deeply into the lungs.
Fomites (Contaminated Surfaces) Inanimate objects transfer pathogens (e.g. door handles, phones, needles). Pathogen survives on the surface for a period.
Faecal-Oral Transmission: Pathogens in faeces contaminate hands, food, or water. Ingested via contaminated water, poor hygiene, undercooked food.
Vector-Borne Transmission: Carried by another organism (vector), typically insects.
How do vaccines help prevent the spread of infectious diseases?
They stimulate the immune system to produce memory cells and antibodies, providing immunity without causing illness.
Name the two ways that pathogenic bacteria cause disease in the human body?
By producing toxins or damaging host tissues
Name 2 viruses that cause respiratory infections
Influenza
SARS
Covid-19
The common cold (adenoviruses, rhinoviruses)
RSV
Give an example of a fungi
Yeast, mushrooms, bread mould, slime mould, etc.
What are endoparasites? Name 2.
Parasites that live inside a host.
Tapeworm, plasmodium (malaria), giardia, blood flukes, hookworm, round worms, pin worms, lung worm, heart worm, etc.
How is Hepatitis C spread?
Via blood-blood contact (e.g. sharing needles, open wounds) or unprotected sexual contact.
A mosquito bites a man in Bali and he develops a fever. The doctors confirm that he has dengue fever. What is the mode of transmission?
Vector-borne, indirect transmission.
Why is it important to complete a full course of antibiotics, even if you feel better?
To ensure all the bacteria are killed and to prevent the development of antibiotic-resistant strains.
Name a bacteria that causes disease in humans and describe the symptoms.
various answers.
examples: E. coli, salmonella - food poisoning
How do viruses replicate?
By invading cells and using host cell machinery to reproduce (e.g. protein synthesis by ribosomes).
No. The visible part of the mould is just the fruiting body (producing spores to reproduce), most of the mould is too small to be seen by the naked eye. The whole loaf is likely infested with mould.
Why are mosquitoes such a dangerous ectoparasite?
They may carry secondary infections or parasites. E.g. dengue fever, malaria, ross-river virus, yellow fever, sleeping sickness, etc.
Common cold, influenza, Covid-19, SARS, Whooping Cough, RSV, etc.
Name 2 common fomites that can transmit the common cold.
door handles, light switches, taps, keyboards, phones, etc.
What is cross-contamination, and how can it be prevented in food preparation?
Cross-contamination is the transfer of pathogens from raw to cooked or ready-to-eat foods. It can be prevented by using separate cutting boards and washing hands and surfaces between tasks.
What is the difference between an endotoxin and an exotoxin?
Exotoxins: Secreted by live bacteria into the surrounding environment. Usually heat-sensitive and highly toxic even in small amounts.Can affect different systems: neurotoxins (brain), enterotoxins (gut), cytotoxins(cells).
Endotoxins: Found in outer membrane of Gram-negative bacteria (lipopolysaccharides). Released when the bacterial cell dies and breaks apart. Cause fever, inflammation, blood vessel damage, and can trigger septic shock.
What is the best method to control/reduce the spread of viruses?
Vaccination
What are the best growing conditions for mould?
Warm, dark, moist, and poorly ventilated environments.
What is the difference between a definitive and an intermediate host?
The definitive host is where the parasite reaches sexual maturity, an intermediate host houses an earlier stage in the lifecycle (larvae or eggs).
Is direct transmission more or less likely in crowded or close-contact settings? Why?
More likely. Because close contact increases the chance of physical interactions or exposure to respiratory droplets, facilitating the spread of pathogens.
Name 3 measures you can take to avoid being infected by an indirect transmission pathway.
Cook food thoroughly (especially meats), sanitise surfaces regularly, avoid being bitten by mosquitoes and other parasites, store food correctly, wear an N95 mask in high risk settings, avoid eating food that has been sitting out, avoid touching your face unless you have washed your hands first.
Explain why food should not be left at room temperature (~24°C) for extended periods.
Because bacteria multiply rapidly in the “danger zone” (between 5°C and 60°C), increasing the risk of food poisoning.
Name 2 special features of bacteria that increase their survival either outside a host or to evade the host immune system.
ability to survive outside a human host
spores or capsules that allow them to survive a long time in soil
ability to rapidly divide by binary fission
ability to swap DNA with each other so antibiotic resistance is easily spread
slimy capsules that protect them from our immune system
ability to change surface proteins so the immune system no longer recognises them
Do antibiotics work against viruses? Explain your answer.
No. Viruses do not have cells and are non-living meaning they lack the structures that antibiotics target.
Why are most fungi unable to be killed by antibiotics?
Most of our antibiotics come from fungi. e.g. penicillin
The brain eating amoeba (Naegleria Fowleri) is what kind of parasite?
a protozoan endoparasite
Name 3 measures that you can take to avoid direct transmission of a respiratory virus if you are sick.
Wash your hands regularly, avoid close contact with others, wear a mask.
Why is controlling indirect transmission often more challenging than direct transmission?
Because pathogens can survive outside hosts on surfaces or in vectors, making it harder to identify and eliminate all sources of infection.
Name and briefly describe two public health measures used to prevent the spread of infectious diseases in a community.
Quarantine: isolating infected individuals to stop disease spread
Sanitation: ensuring clean water, waste disposal, and food safety