B3 - Infection and response

Pathogen

A micro-organism that causes disease

Bacteria

Very small single-celled organisms (prokaryotes) that can cause diseases e.g. salmonella and gonorrhoea.

Viruses

Even smaller than bacteria, they are not cells. Must replicate within a 'host cell' e.g. HIV, measles and tobacco mosaic virus.

Fungi

Eukaryotic organisms some of which can cause diseases e.g. Rose black spot and Athlete's foot.

Protist

Eukaryotic organisms that can cause disease e.g. Plasmodium which causes malaria.

Communicable disease

An infectious disease that can spread from one organism to another.

Transmission

How a pathogen is passed from one organism to another

Transmission by direct contact

A method of spreading disease e.g. by contact or touch

Transmission by water

Spread of disease by drinking or coming into contact with water that contains pathogen e.g. spread of cholera

Transmission by air

Spread of disease where pathogen is carried in airborne droplets that are breathed in e.g. measles, flu, the common cold

How do viruses damage our bodies and make us feel ill?

Replicate rapidly within cells causing cells to 'burst'.

Toxins

Produced by bacteria and cause damage to cells

Measles

Cause: Virus
Spread: Air droplets
Symptoms: Rash, fever, potentially fatal complications
Treatment: None

HIV

Cause: Virus
Spread: Direct contact with contaminated blood or semen
Symptoms: Early - flu-like
Late - destroys immune system leaves prone to other infections
Treatment: Drugs that stop virus replicating

Tobacco mosaic virus (TMV)

Cause: Virus (affecting plants)
Spread: From one plant to another
Symptoms: Discolouration of leaves meaning that plants cannot photosynthesise as well thereby reducing growth.
Treatment: None

Salmonella

Cause: Bacteria
Spread: Eating contaminated food
Symptoms: Fever, vomiting, diarrhoea
Treatment: Antibiotics if severe

Gonorrhoea

Cause: Bacteria
Spread: Direct sexual contact (STD)
Symptoms: Pain when urinating, yellow/green discharge
Treatment: Antibiotics

Rose black spot (plant disease)

Cause: Fungi
Spread: From one plant to another
Symptoms: Black spots on leaves, eventually leaves turn yellow and fall off. Plant not able to photosynthesise well - poor growth.
Treatment: None

Malaria

Cause: Protist
Spread: Being bitten by mosquito carrying malaria protists.
Symptoms: Recurrent bouts of fever
Treatment: Drugs to stop replication of protist

Vector

An organism that spreads disease without directly causing it e.g. mosquito ( and malaria)

Methods to prevent spread of disease

Good hygiene e.g. hand washing, clean drinking water
Vaccination
Testing for disease
Barrier methods e.g. condoms
Destroying vectors e.g. killing mosquitoes, or preventing them from breeding
Using mosquito nets

Non-specific defence systems

Skin - barrier
Nose - mucus and hairs
Trachea and bronchi - mucus and cilia (very small hairs)
Stomach - acid

Ways that white blood cells defend against pathogens?

Release of anti-toxins, release of antibodies and phagocytosis

Phagocytosis

White blood cells engulf and digests pathogens.

Anti-toxin

Released by white blood cells, neutralises toxins released by bacteria

Antibody

Attaches to antigens on pathogens which is then recognised and phagocytosed by white blood cell.

Antigen

Molecule on surface of pathogen that is recognised by immune system as 'foreign'

Vaccine

Contains dead or inactive pathogens that carry antigens to be recognised by the immune system.

Primary immune response

First encounter with pathogen/vaccine
Slow response.
White blood cells produce small amounts of antibodies.
Memory cells are created.

Secondary immune response

Pathogen re-enters the body.
Memory cells respond very quickly to produce high levels of antibodies.
Response is slow to reduce.
Speed and scale of response prevent infection.

Herd immunity

A large proportion of the population are immune due to vaccination therefore it is less likely to come into contact with somebody who isn't immune. Disease is less likely to spread.

Antibiotic

A drug used to treat BACTERIAL infections. Specific antibiotics are used to treat specific bacteria.
Not effective against viruses.

Antibiotic resistance

Strains of bacteria that are no longer killed by an antibiotic ( due to mutations). e.g. MRSA

Painkillers e.g. paracetamol or Ibuprofen

Treat symptoms but do NOT kill pathogens

Digitalis (heart drug) and aspirin

Drugs that were originally discovered and produced from plants.

How are drugs made now?

Chemically synthesised in labs by pharmaceutical companies

Testing for toxicity

New drugs are tested to see if they are safe to use

Testing for efficacy

New drugs are tested to see if they have the 'desired affect' (if they work)

Testing for dose

New drugs are tested to see at what dose they are most effective

Preclinical trials

Testing on cells, then tissues, then live animals

Clinical trials

Drug given first to healthy volunteers
If successful then a suitable dose is found
Then tested in double blind trial using patients and a placebo

Double blind trial

Patient is given either the drug or a placebo.
Neither patient, nor doctor, knows whether they have drug or placebo.

Placebo

A substance that appears like the drug being tested but has no effect.

Penicillin

Drug that was originally discovered and produced by microorganisms (fungi).