Communicable diseases

Pathogens are microrganisms that enter the body and cause disease.

They cause communicable diseases which are diseases that can spread easily.

Both plants and animals can be affected by communicable diseases.

Bacteria

Bacteria are very small living cells that reproduce rapidly inside your body.

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

Viruses

Viruses are not cells and are much smaller

Like bacteria they reproduce rapidly inside your body.

They live inside your cells and replicate using the cells machinery to form many copies of themselves. The cell will eventually burst releasing all new viruses. This cell damage makes you feel ill.

Protists

They are single celled eukaryotes. Some are parasites which live on or inside other organisms causing damage. They are often transferred by vectors which dont get the disease themself.

Fungi

Some are single celled and others are made up of a body called hyphae.

These hyphae can grow and penetrate human skin and the surface of plants causing disease. They can also produce spores which spread to other plants and animals.

Ways pathogens are spread:

• Air - some airborne pathogens are picked up from an infected persons cough or sneeze.

• Water - Pathogens can be picked up when bathing or drinking dirty water

• Direct contact - Touching contaminated surfaces like skin

Viral diseases

Measles is a viral disease. Its spread by droplets from an infected persons cough or sneeze. Symptoms are red skin rash or high fever. It can be very serious or even fatal if their are any complications for example it can lead to pneumonia. Most people are vaccinated against measles when they are very young.

HIV is a viral disease spread by sexual contact or by exchanging bodily fluids when taking drugs. It initially causes flu like symptoms for a few weeks then nothing for years. During this time it can be controlled using Antiretroviral drugs to stop the virus replicating around the body. It usually targets immune cells. If the bodies immune system is badly damaged then it cant cope with diseases such as cancer.

Tobacco mosaic virus is when a mosaic pattern develops on the leaves of plant meaning parts of a leave become discoloured. This discolouration means that plants cant carry out photosynthesis.

Fungal disease

Rose black spot is a fungus that causes purple or black spots to develop on leaves of plants. The leaves then turn yellow and drop off. This means that less photosynthesis takes place so the plant wont grow well. It spreads through the environment by water or wind.They are treated using fungicides or stripping the plant off its infected leaves. These leaves then need to be destroyed so that the fungus doesnt spread to other plants.

Bacteria diseases

Salmonella is a type of bacteria that causes food poisoning. Symptoms are fever, vomiting, cramps and diarrhoea. These symptoms are caused by toxins produced by the bacteria. You get it by eating food which has been contaminated by the bacteria. In the UK most poultry has been vaccinated against it to control the spread of the disease.

Gonorrhoea is a sexually transmitted disease. Its passed on by sexual contact and is a bacteria. Symptoms are pain when urinating or a yellow or green discharge from the vagina or penis. It was originally treated with pennicillin but now its been trickier now that bacteria has become resistant to the antibiotics. It can be prevented using antibiotics or contraception.

Ways to prevent disease:

• Isolating individuals

• Vaccination

• Destroy vectors

• Stay hygienic

Human defence responses

The skin - Acts as a barrier to pathogens. It also secretes antimicrobial substances which kill the pathogens.

Nose - Hair and mucus in your nose trap particles which may contain pathogens

Stomach - Produces HCL which kills pathogens that makes it far from the mouth.

Trachea and Bronchi - secretes mucus to trap pathogens. They are also lined with cilia which are hair like structures that waft the mucus to the back of the throat where they can be swallowed.

Ways White blood defends against pathogens :

• Phagocytosis - White blood cells engulf foregin cells and digest them

• Produce antibodies - When white blood cells come across an invading antigen they will produce antibodies to lock onto the invading cell so that they can be found and destrpyed. The antibody produced would then be specific to that one antigen therefore antibodies would be produced rapidly and carried around the body to find all similar bacteria and viruses. If the person is infected with the same pathogen again then the white blood cells will rapidly produce antibodies to kill it. The person is then naturally immune to that pathogen and wont get ill.

• Produce antitoxins - These counteract toxins by the invading bacteria.

Vaccination

Vaccines involve injecting small amounts of dead or inactive pathogens. These carry antigens which cause your white blood cells to produce antibodies to attack them, even though they are harmless.

This means that if live pathogens appear after that then your white blood cells can rapidly mass produce antibodies to kill them off.

Advantages of Vaccines :

• They have helped control lots of diseases that were once common in the UK

• Epidemics can be prevented if a large percentage of the population are vaccinated. This means that even the people who arent vaccinated are unable to catch the disease due to very little people able to pass it on. But if a significant number of people arent vaccinated then the disease will spread quickly through them and lots of people will be ill at the same time

Disadvantages of Vaccines :

• They dont always work

• You can sometimes experience a bad reaction like a seizure

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Antibiotics and painkiller

Painkillers are drugs that relieve pain but dont actually tackle the cause of the disease, only reduce symptoms.

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Antibiotics are drugs that kill the bacteria causing the problem without killing your own body cells.

When you have an infection its possible that the bacteria can become resistant to the antibiotics. This means that when you treat an infection only the non resistant strains will be killed. The individual resistant strain will survive and reproduce increasing its population.

Developing drugs

• The first stage is preclinical testing where drugs are tested on human cells and tissues in a lab. However you cant test them on human cells an tissues that affect whole or multiple body systems.

• Once doing this, you then test drugs on live animals. This is to test the efficacy of the drug, to find out about its toxicity and to find the best dosage.