Infection and response

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Communicable Disease

Pathogens are microorganisms that nter the body and cause infectious diseases both in plants and animals.
Bacteria are small cells which can reproduce rapidly in the body, producing poisonous toxins which damage cells and tissue.
Viruses also reproduce rapidly but are not cells. They live inside body cells, using the cell's machinary to make copies of itself. The cell will then burst, releasing the virus.
Protists are mostly single-celled and they are all eukaryotes. Some are parasites whick live on or in other organisms, transfered by a vector.
Some fungi are also single-celled, others have a body made up of hyphae which can grow and penetrate human skin and the surface of plants. It also produces spores which can spread to other plants and animals.
Pathogens can be spread in three many ways:
Water - by drinking dirty or bathing in dirty eater, e.g. Cholera.
Air - pathogens can be breathed in air droplets, e.g. The influenza virus.
Direct - picked up by touching contaminated surfaces, including the skin e.g. Shower floors.

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Viral diseases.

Measles - spread by droplets from an infected persons sneeze or cough. Symptoms include rash and fever and complications can cause fatality, for example it can lead to pnemonia or a brain infection called encephalitis. Most people are vaccinated when young.
HIV - spread by sexual contact or exchanging bodily fluids, for example sharing needles. Initially causes flu-like symptoms. The virus attacks the immune system, leaving the immune system badly damaged so it cannot cope with other infections or cancers. At the late stage HIV is known as aids. Can be treated if cought early with antiretroviral drugs.
Tobacco mosaic virus - effects plants, for example tomatoes, and causes a mosiac pattern in the leaves of the plant and a diclourment, meaning it can not carry out photosynthesis as well, stunting its growth.

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Roe black spot and Malaria

Rose black spot - a fungus which causes blue or black spots to develop on leaves of rose plants, causing the leaves to turn yellow and drop off, meaning less photosynthesis and stunted growth. Can be treated by using fungicides and by striping the plant of its infected leaves and destroying the leaves to prevent spread.

Malaria - caused by a protist. Part of the life cycle is within a mosquito who picks up the disease from an infected animal. When it feeds on a healthy animal, it passes on the disease. Malaria causes repeated episodes of fever and can be fatal. It can be prevented by stopping mosquitos breed ot by using insecticides and mosquito nets.

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Bacterial Diseases

Salmonella - bacteria which causes food poisoning and causes fecer, stomach cramps, vomiting and diarrhoea caused by toxins produced by the bacteria. Can be got from eating contaminated food either whilst the poultry was alive or by being orepared in unhygenic conditions. In the UK most poultry is vaccinated against salmolla to control its spread.

Gonorrhoea - a sexually transmitted disease caused by bacteria. Symptoms include pain whilst urinating and a thick green or yellow discharge from the vagina or penis. Originally treated using penicillin (an antibiotic) but some strains of bacteria have now become resistant to it. Can be prevented using barrier methods of contraception.

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Preventing the spread of disease

Being hygienic - for example washing your hands before cooking or after sneezing.

Destroying vectors - prevents the disease being carried. Can destroy insects by using insecticides or by destroying their habitat so they can no longer bread.

Isolating infected individulas - prevents the disease from being caught.

Vaccination - means they can not develop the infection and then oass it on to someone else.
Vaccinations involve injecting small amounts of dead or inactive pathogens which carry antigens which cause the body's white blood cells to produce antibodies to attack them, meaning the white blood cells can rapidly mass-produce antibodies to kill off the oathogen if you get infected later (otherwise it would take a few days).
Pros - helped control many communicable diseases which were once common in the UK. Big outbreaks of disease, epidemics, can be prevented if a large percentage of the population is vaccinated.
Cons - dont always work. Some people can get a bad reaction.

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Fighting Disease

The skin acts as a barrier to pathogens and secretes antimicrobial substances which kill pathogens.
Hairs and mucus in your nose trap particals which carry pathogens.
The trachea and beonchus secrete mucus to trap pathogens. They are also lined with hair-like structures called cilia which waft the mucus up to the back of the throat where it can be swollowed.
The stomach produces hydrochloric acid to kill pathogens.
Immune system:
White blood cells travel around the blood, patrolling for microbes. When they come across one three stages occur:
Consuming - white blood cells engulf foreign cells and digest them (phagocytosis).
Producing Antibodies - every invading pathogen has uniques molecules (antigens) on its surface. When some white blood cells come across foreign antigens they produce proteins called antibodies to lock onto the invading cells so they can be found and destroyed by other white blood cells. Antibodies are then produced rapidly and carried around the body.
Producing antitoxins - these conteract toxins produced by the invading bacteria.

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Drugs

Painkillers - drugs which relieve pain but do not treat the cause of the disease or kill pathogens. 'Cold remedies' are similaras they also only treat the symptoms.
Antibiotics - kill or prevent the growth pf the bacteria causing the problems without killing your own body cells Different antibiotics treat different types of bacteria. They can not be used to treat viral infections as viruses reproduce using your body cells.
Bacteria can mutate to become resistant to antibiotics. This means when treated only the non-resistant strains if bacteria will be killed and the resistant will survive and reproduce, increasing the population of the resistan-strain. This is an example of natural selection. The resistant strain could cause a serious infection that cant be treated using antibiotics. To slow down the rate of developing resistant strains doctors should not over-subscribe and you should finish the whole cource of antibiotics.
Plants produce a variety of chemiclas to defend themselves against themseleves against pests and pathogens. Some of these chemicals can be used as drugs to treat humans or relieve symptoms. For example, asprin was developed from a chemical found in willow and digitalis which is used to treat heart conditions was developed from foxgloves. Penicillin was found in a petri dish where a mould (penicilin) killed the bacteria.
Most modern drugs in the pharmaceutical industry are synthesised by chemists in labs.

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Developing drugs

Prenclinical testing - teted on human cells and tissue in labs, however this can not be used to see how the drug affects the whole or muliple body systems.

The drug is then testen in live animals to test efficiency, toxicity and to find the best dosage. Must be treated on two different live mammals.

Clinical trail - tested on human volunteers, first on healthy volunteers to make sure it doesnt have any harmful side effects. At the start a very low dosage is given, then it is gradually increased. The drug is then tested in people with the illness and the optimum dosage is found for the most effective results with few side effects.

Patients are randomly put into two groups, one is a placebo so the doctor can see that the drug actually works, allowing for the placebo effect.

Clinical trials are blind or sometimes double blind, where neither the doctor or the patient knows which one is real so the doctors monitoring the patients are not subconsciously influenced by their knowledge. The results are not punlished until they have been peer-reviewed, prevented biasness or false claims.

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