Infection, Disease and Response

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Communicable Disease

Several types of pathogens

Pathogens are micro-organisms that enter the body and cause disease

Cause communicable (infectious) disease - easily spread

Both plants and animals can be infected

Bacteria

Very small cells - can reproduce quickly inside body

Can make you feel ill by producing toxins - damage cells and tissues

Viruses

Not cells

Tiny, about 1/100th of the size of bacterium

Reproduce rapidly inside your body

Live inside cells and replicate themselves using cells' machinery to produce many copies of themselves

Cell will usually then burst, releasing new viruses

Protists

Eukaryotes and most are single celled

Some protists are parasites

Live on or in other organisms and can cause them damage

Often transferred to organism by a vector

Doesn't get the disease itself

Fungi

Some are single-celled

Others have a body - made up of hyphae

Hyphae can grow and penetrate human skin and surface of plants, causing disease

Can produce spores

Can be spread to other plants and animals

Pathogens can be spread in different ways

Water

Some pathogens can be picked up drinking or bathing in dirty water

Air

Can be carried in the air and can then be breathed in

Some airborne pathogens are carried in the air in droplets

Direct Contact

Can be picked up by touching contaminated surfaces

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Viral, Fungal and Protist Diseases

Viral Diseases

Measles

Spread by droplets from infected person's sneeze or cough

Develop a red skin rash

Show signs of fever

Can be very serious

Can lead to pneumonia or a brain infection

Most people are vaccinated when young

HIV

Spread by sexual contact, or by exchanging bodily fluids

Can happen when people share needles when taking drugs

Initially causes flu-like symptoms

Can be controlled with antiretroviral drugs - stop virus replicating

Attacks immune system

If immune system is damaged, it can't cope with other infections or cancers

Tobacco Mosaic Virus

Affects many species of plants

Causes mosaic pattern on leaves

Parts of leaves become discoloured

Discolouration means plants can't carry out photosynthesis

Fungal Diseases

Rose Black Spot

Causes purple or black spots to develop

Leaves can turn yellow and drop off

Less photosynthesis so plant growth is affected

Spreads in water or by wind

Treated with fungicides and by stripping plant of affected leaves

Leaves need to be destroyed so fungus doesn't spread

Disease caused by protist

Malaria

Mosquitos are vectors - pick up malarial protist when they feed on infected animal

Every time mosquito feeds on another animal, it infects it by inserting protist into blood vessels

Causes repeating episodes of fever

Can be fatal

Spread of malaria can be reduced by stopping mosquitos from breeding

Protected using insecticides and mosquito nets

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Bacterial Disease and Preventing Disease

Bacterial Diseases

Salmonella

Causes food poisoning

Infected people can suffer from fever, stomach cramps, vomiting and diarrohea

Caused by toxins that bacteria produce

Eating food that's contaminated

In the UK, most poultry are given a vaccination to control spread of disease

Gonorrhoea

Sexually transmitted infection

Passed by sexual contact

Pain when urinating

Originally treated with penicillin

Strains of bacteria have become resistant to it

Prevent spread of it - people can be treated with antibiotics and should use barrier methods of contraception

Spread of diseases can be reduced or prevented

Being hygenic - washing hands before preparing food or after sneezing

Destroying vectors - killed using insecticides or by destroying habitats so they can no longer breed

Isolating infected individuals - prevents spread of disease/passing on to someone else

Vaccination - can't develop infection and can't pass it onto someone else

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Fighting Disease

Body has features to stop things getting inside

Skin

Acts as barrier to pathogens

Secretes antimicrobial substances which kill pathogens

Hairs and mucus

Trap particles that could contain pathogens

Trachea and bronchi

Secrete mucus to trap pathogens

Lined with cilia, which waft mucus up to the back of the throat where it can be swallowed

Stomach

Produces hydrochloric acid

Which kills pathogens

Immune system can attack pathogens

Immune system kicks in to destroy them

Most important part of immune system is white blood cells

WBC travel around blood and constantly check for microbes

Three lines of attack

White Blood Cells

Consuming them - engulf foreign cells and digest them

Phagocytosis

WBC recognises pathogen is foreign

Engulfs pathogen

Produces lysozymes to digest pathogen

Pathogen is expelled by WBC

Producing antibodies

Specific proteins on surface of them

When WBCs come across a foreign antigen, they will begin to produce antibodies to lock onto invading antigens - can be found and destroyed by other WBCs

Antibodies are specific to that type of antigen

Will not lock onto any other type of antigen

Produced rapidly and carried around body

WBCs can recognise antigens and will know how to rapidly produce antibodies to kill it

Person is naturally immune to pathogen

Producing antitoxins

Neutralise toxic chemicals released by pathogens

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Vaccination

When you're infected with a new pathogen, it takes WBCs a while to learn how to deal with it

Vaccinations involve injecting small amounts of dead or inactive pathogens

Carry antigens - cause body to produce antibodies to attack them

Memory cells can remember how to produce these antibodies and when to produce them

If you become infected, body can treat it quickly as it knows what antibodies to produce

Pros of vaccination

Helped to control lots of communicable diseases

Large outbreaks of disease can be prevented

Even people who haven't been vaccinated are unlikely to catch it

Cons of vaccination

Sometimes have bad reaction to a vaccine

Bad reaction are rare

Vaccines don't always work

Sometimes they won't give immunity

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Fighting Disease - Drugs

Painkillers are drugs - relieve pain - but don't tackle cause of disease/kill pathogens

Other drugs reduce symptoms

Antibiotics - kill bacteria causing the problem (doesn't kill body cells)

Different antibiotics kill different types of bacteria

Don't destroy viruses

Viruses reproduce using body cells - difficult develop drugs that don't destroy body cells

Use of antibiotics has greatly reduced, number of deaths caused by bacteria

Bacteria can mutate - cause them to be resistant to antibiotics

If you have an infection, some bacteria might be resistant to antibiotics

Means when you treat the infection, only non-resistant strains of bacteria will be killed

Individual resistant bacteria will survive and reproduce

Resistant strain could cause a serious infection - can't be treated by antibiotics

To slow down the rate of development of resistant strains - important to avoid over prescribing antibiotics

Important that you finish whole course of antibiotics and don't stop when you feel better

Plants produce a variety of chemicals to defend themselves against pests and pathogens

Some of these chemicals - used as drugs to treat human disease or relieve symptoms

Aspirin

Painkiller and lowers fever

Developed from a chemical found in willow tree

Digitalis

Treats heart conditions

Developed from chemical found in foxgloves

Some drugs were extracted from micro-organisms

Fleming discovered penicillin which is mould that kills bacteria

Drugs are made on large scale in pharmaceutical industry - synthesised in labs - process may start with chemical from a plant

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Developing Drugs

Three main stages in drug testing

1. Preclinical Testing

Drugs are tested on human cells and tissues in lab

Can't use human cells and tissues to test drugs that affect whole or multiple body systems

2. Testing on live animals

Tests efficiency, to find about toxicity and best dosage

In Britain, a new drug must be tested in two different live mammals

Some think this is cruel - others believe it's the safest way to make sure drug isn't dangerous

3. Testing on human volunteers

Drug is tested on healthy volunteers (first)

Make sure it isn't harmful/have harmful side effects

At start of trial small dose is used and then gradually increased

If results are good, drugs can be tested on people suffering from illness

Optimum dosage is found - most effective and has few side effects

Patients are given either drug or placebo - test how well it works

See difference drug makes - allows placebo effect

Clinical trials are blind

Patient doesn't know whether they're getting the drug or placebo

Often double-blind - neither patient or doctor knows until all results have been gathered

Doctors aren't influenced

Results f drug testing and drug trials aren't published until they've been through peer review

Helps to prevent false claims