Health and Disease

Health = A state of physical and mental well-being

Communicable diseases are caused by pathogens e.g. bacteria and viruses. Non-communicable diseases cannot be transmitted from one person to another e.g. heart disease and arthritis

Other factors can affect health:

Diet - If you do not eat enough, or get the right nutrients, you may suffer from starvation or anemia. Too much food, or the wrong type of food, can lead to obesity and type 2 diabetes.

Stress - Everyone experiences a degree of stress, but too much stress can trigger heart disease and mental health problems.

Life Situations - E.g. where you live and who you are, can have a big effect on your health and cause communicable and non-communicable diseases.

Different diseases and health conditions happen at the same time. They interact and often one problem makes another worse. For example:

- Viruses living in cells can trigger changes that lead to cancers e.g. human papilloma virus can cause cervical cancer.

- If your immune system is defective, you will be more likely to suffer from communicable diseases.

- A pathogen (e.g. a cold) can trigger allergies to factors in the environment.

- Physical and mental health are closely linked.

Communicable diseases are caused either directly by a pathogen or by a toxin made by the pathogen. The pathogen can be passed from one infected person to another non-infected individual. 

Bacteria and viruses cause the majority of communicable diseases in people. In plants, viruses and fungi are the most common pathogens.

Bacteria = Single-celled living organisms.

Viruses = Even smaller than bacteria, cause diseases in every type of living organism.

Pathogens cause disease by:

- Bacteria divide rapidly by splitting in two. May produce toxins that make you feel ill. Sometimes damage your cells.

- Viruses take over the cells in your body. They live and reproduce inside the cells, damaging and destroying them.

Ignaz Semmelweis proved that some kind of infection was being passed on to women giving birth by doctors who had not washed their hands.

Louis Pasteur was a French scientist, that proved that microorganisms cause disease.

Joesph Lister developed antiseptic chemicals to destroy pathogens.

Microscopes allowed people to see pathogens.

We can prevent the spread of communicable diseases by:

Better hygiene

Vaccination

Isolating infected individuals

Controlling vectors (e.g. Mosquitos and Malaria)

Measles

• Spread by droplet infection.
• It causes fever and a rash. Can be fatal. There is no cure. Isolation of patients and vaccination prevent spread.

HIV/AIDS

• Initially, causes flu-like illness. Unless it is controlled by antiretroviral drugs the virus attacks the immune cells.
• AIDS occurs when the immune system is so damaged it cannot deal with infections or cancers.
• Spread by sexual contact or the exchange of body fluids. When drug users share needles.

Tobacco Mosaic Virus

• Spread by contact and vectors.
• It damages a reduces photosynthesis.
• No treatment, prevented by field hygiene and pest control.

Salmonella

• Spread through undercooked food and poor hygiene.
• Symptoms include fever, cramps, diarrhoea and vomiting caused by the toxins.
• In the UK, poultry is vaccinated against Salmonella.

Gonorrhoea

• An STD.
• Symptoms include discharge and pain on urination.
• Treatment includes antibiotics, but many strains are now resistant.
• Using condoms and limiting sexual partners prevents spread.

There are very few fungal diseases that affect people, e.g. Athletes Foot. In plants, fungal diseases are common. 

Rose Black Spot (Fungi)

• Spread by wind and water.
• It damages leaves so they drop off, affecting growth and photosynthesis.
• Controlled by removing infected leaves and chemical sprays, but is not effective.

Malaria (Protist)

• Cuased by parasitic protists and spread by the bite of female mosquitoes.
• It damages blood and liver cells, causes fevers and shaking, can be fatal.
• Some drugs are effective if given early but protists are becoming resistant.
• Spread is reduced by preventing the vectors from breeding and using mosquito nets.

These include skin, tears, stomach acid, mucus and cilia in the respitory tract, scabs.

What happens if pathogens do get inside you?

White blood cells work in three ways:

1. They ingest them

2) They make antibodies that kill the pathogen

3) They make antitoxins that counteract the poisons produced by the pathogens

When you damage or cut your skin:

• You bleed
• The platelets in your blood form a clot
• The clot becomes a scab, selling the cut, stopping pathogens getting in and you bleeding to death.

Your skin produces antimicrobial secretions to destroy pathogenic bacteria.