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).