B3 - Infection & Response

What is a communicable disease?

A disease that can be spread between organisms

What causes communicable diseases?

Pathogens – bacteria, viruses, protists, fungi

What are pathogens?

Microorganisms that enter the body and cause disease

How do pathogens cause disease?

By producing toxins or damaging cells

How are pathogens spread?

Through air, water, or direct contact

How can the spread of disease be reduced?

• Hygiene

• Destroying vectors

• Isolation

• Vaccination

How do viruses reproduce?

They invade host cells and use their subcellular structures to make copies of themselves

What happens when virus-infected cells burst?

They release new viruses and cause cell damage

What causes measles, and how is it spread?

Measles is a virus

It is spread by droplets from coughs and sneezes

What are the symptoms of measles, and why is it serious?

Symptoms include fever and red skin rash

It can lead to pneumonia or brain infection

How is it prevented?

Most people are vaccinated when young

What is HIV, and how is it spread?

A virus that attacks the immune system

It’s spread by sexual contact or exchange of bodily fluids such as blood

What symptoms does HIV cause?

It causes flu-like symptoms

What happens if HIV is untreated?

It can lead to AIDS

How is HIV controlled?

Antiretroviral drugs stop viruses replicating

What is TMV

Tobacco Mosaic Virus is a virus that affects many species of plants

What are the symptoms of TMV

Mosaic pattern on the leaves and discolouration

How does TMV affect the plant?

Reduces photosynthesis an growth

What is Bacteria?

They are very small cells which reproduce very quickly

They make you feel ill by producing toxins that damage cells and tissues

What is salmonella?

A bacteria that causes food poisoning

What are the symptoms of salmonella?

Fever, stomach cramps, vomiting, and diarrhoea

How is salmonella spread?

By eating contaminated food

How is it prevented?

Poultry are vaccinated against salmonella

Cook food thoroughly

What is gonorrhoea and how is it spread?

A sexually transmitted disease that spreads by sexual contact, e.g., unprotected sex

What are the symptoms of gonorrhoea?

• Pain when urinating
  

• Thick yellow or green discharge

Why is it harder to treat now?

Strains of bacteria have become resistant to antibiotics

How can it be prevented?

• Barrier methods of contraception such as condoms
  

• Treating infected people with antibiotics

What are fungi?

Fungi are single-celled, or they are made of hyphae (thread-like structures)

What does fungi do?

They grow and penetrate human skin and the surfaces of plants, causing diseases

Hyphae can produce spores, which spreads to other plants

What is rose black spot?

A fungus that causes purple/black spots on the leaves of rose plants

How does it affect the plant?

Leaves turn yellow and drop off

This leads to less photosynthesis so the plant doesn’t grow very well

How is it spread, and how can it be treated?

• Spread by water or wind
  

• Treated by fungicides and removing infected leaves

What are protists?

They are single-celled eukaryotic organisms

What causes malaria, and how is it spread?

• Caused by a protist carried by mosquitoes
  

• Mosquito bites transfer the protist

What are the symptoms of malaria?

Recurring fever and tiredness

How is malaria controlled?

• Stopping mosquitoes from breeding
  

• Insecticides
  

• Mosquito nets

How is malaria treated?

By using antimalarial drugs

What are the body’s first line of defences?

Skin, nose, trachea, bronchi, and stomach acid

How does the skin defend the body?

• Produces oils that kills or slows down microbes
  

• Acts as a barrier to stop germs getting in

How does the nose defend the body?

The nose hairs and mucus trap dust, dirt, and microbes

How does the trachea and bronchi defend the body

• Produces mucus to trap pathogens
  

• Tiny hairs called cilia waft the mucus up to the throat, where it can be swallowed

How does the stomach defend the body?

Produces hydrochloric acid which kills pathogens

What is the role of white blood cells?

Engulf pathogens, make antibodies, make antitoxins

What are antibodies?

Proteins that bind to antigens on pathogens

What are antitoxins?

Substances that neutralise toxins

What is phagocytosis?

1. WBC detects pathogen and moves towards it
   

2. A phagocyte surrounds the pathogen and engulfs it
   

3. A phagocyte releases enzymes which breaks down and digest the pathogen

What are lymphocytes?

White blood cells that make antibodies and antitoxins

How do white blood cells attack pathogens using antibodies?

1. Lymphocytes detect antigens on surface of pathogens.
   

2. Lymphocytes make specific antibodies that match antigens
   

3. Antibodies attach to antigens which triggers the pathogen to be destroyed

What is a vaccination?

• It involves injecting a dead or weakened form of a pathogen into the body
  

• White blood cells are stimulated to produce antibodies to attack the pathogens
  

• The body creates memory cells which remember the pathogen
  

• If real pathogen enters the body later, the immune system recognises it quickly, producing antibodies faster, which prevents infection

What is herd immunity?

When most of the population is vaccinated, so the spread of disease is reduced

What do antibiotics do?

They kill or stop the bacteria growing inside the body

Why don’t antibiotics kill viruses?

Viruses reproduce inside body cells

What do painkillers do?

They relieve the pain, but don’t kill the pathogens

What is antibiotic resistance?

When bacteria mutate making them resistant to antibiotics

How can you reduce antibiotic resistance?

Avoid overusing antibiotics and finish full courses

Where were many drugs originally extracted from?

Plants and microorganisms

Who discovered penicillin?

Alexander Flemming

What happens in preclinical testing?

Drugs are tested on cells, tissues, and animals.

This is to test the efficacy, find out its toxicity, and find the best dosage

What happens in clinical testing?

Drugs are tested on healthy volunteers to make sure the drug doesn’t have any harmful side effects

If results on volunteers are good, drugs are tested further to find the optimal dose 
(dose of drug that is most effective with few side effects)

What is a placebo?

A substance with no active drugs

What are double-blind trials

Neither the doctor nor patient knows who has the real drug or placebo

What needs to happen before the results of drug testing and trials are published?

The results need to go through peer review, which helps to prevent false claims