B5

Health is a state of physical and mental well-being.

Communicable (infectious) diseases:

• E.g. Tuberculosis and flu
• Caused by pathogens such as bacteria and viruses, that can be passed on to one another.

Non-communicable diseases:

• E.g. heart disease and arthiritis 
• Cannot be transmitted from one person to another

Diet:

Eating too little food or the wrong nutrients can lead to:

• Starvation
• Anemia
• Rickets

Too much food or the wrong type of fiid can lead to:

• Obesity
• Some cancers
• Type 2 diabetes

Stress:

Too much stress is linked to an increased risk of heart disease, certain cancers and mental health problems.

• Depending on the part of the world where you live, you will have an increased risk of certain health problems (e.g. malaria in tropical regions)
• Gender, financial status, ethnic group, and the number of children in a family also affect which disease people are most at risk from.
• If free health care is provided, this will reduce the risk and effect of many conditions.
• Local sewage and rubbish disposal systems are important for a healthy populations

A person can have different types of disease and health conditions at the same time, and these often interact.

• Viruses living in cells, such as the human papilloma virus, can trigger changes that lead to cancers.
• Defects in the immune system can make someone more likely to have a communicable disease.
• Immune reactions can trigger allergies.
• Severe physical health issues can lead to mental health problems, such as depression.
• Malnutrition can lead to deficiency diseases, a weakend immune system, obesity, cardiovascular disease, type 2 diabetes, or cancer.

Communicable diseases or infectious diseases are cause by microorganisms called pathogens. These include bacteria, viruses, fungi, and protists.

• Bacteria and viruses are the pathogens that cause most communicable diseases in humans, Viruses and fingi cause most diseases in plants.
• When bacteria or viruses enter the body they reproduce rapidly.
• Bacteria can make you feel ill by producing toxins (poisons) and may also damage the body cells.
• Viruses are much smaller than bacteria and reproduce inside cells, damaging and destroying the cells.

Air:

• Bacteria, viruses, and fungal spores can be spread through the air from one animal or plant to another.
• Humans spread pathogens when they cough or sneeze. The droplets of water carrying the pathogens are inhaled by another person. This is called droplet infection.

Water:

• Drinking contaminated water can allow pathogens to enter the digestive system.
• Fungal spores in splashes of water can spread plant diseases.

• Sexually transmitted infections can be passed by sexual contact.
• Some pathogens are transmitted by skin contact or enter via cuts, scratches, or needle punctures.
• Animals such as mosquitoes can act as vectors and carry pathogens from one individual to another.
• If a portion of a diseased plant is left in a field it could infect the whole crop.

Our modern understanding of pathogens comes from the work of pioneering doctors and scientists in the 19th century, such as ignaz Semmelweis, Louis Pasteur, and Joseph Lister.

• Ignaz Semmelweis was a doctor working before bacteria and viruses had been discovered. He realised that infection could be transferred from person to person in a hospital.
• Semmelweis tod his staff to wash their hands between treating patients. This reduced the number of deaths. We now know that he was right, but at the time, othr doctors did not take him seriously.
• Louis Pasteur showed that microorganisms cause disease. He developed vaccines against anthrax and rabies.
• Joseph Lister started to use antiseptics to destroy pathogens in operating theatres.

There are a number of key ways to help prevent the spread of communicable diseases.

Hygeine:

• Hand washing, especially after using the toilet, before cooking, or after contact with an animal or someone who has an infectious illness.
• Using disinfectants on kitchen work surfaces, toilets, etc.
• Keeping raw meat away from food that is eaten uncooked.
• Coughing or sneezing into a handkerchief, tissue, or your hands (and then washing them)
• Maintaining the hygeine of people and agricultural machinery to help prevent the spread of plant diseases.

Vaccination:

• A small amount of a harmless form a specific pathogen is introduced into your body. This prepares the immune system so you are protected from future infection.
• Plants cannot be vaccinated against dissease as they do not have an immune system.

• If someone has an infectious disease such as ebola they need to be kept in isolation to prevent the pathogen being passed on.
• Small plants infected with diseases can be moved and destroyed.

Some communicable diseases are passed on by vectors.

• Mosquitoes, houseflies, and rats carry many human pathogens between people.
• Aphids and some beetles transmit plant pathogens.
• Destorying th vectors controls the spread of disease.

• The main symptoms of measles are fever and a red skin rash.
• It is spread by droplet infection.
• Measles is a serious disease that can be fatal.
• An infected person should be isolated.
• Measles can be prevented by vaccination.

• HIV is virus that can lead to AIDS.
• The early symptoms may be mild and flu-like.
• HIV attacks the immune system eventually resulting in AIDS. It may take several years to develop AIDS, depending on a person's general health, level of nutrition, and access to antienvironmental drugs. In Sub-Saharan Africa most people with HIV infection do not have access to these drugs.
• HIV is spread by direct sexual contact or by infected blood (from shared needles) or breast milk.
• The spread of HIV can be prevented by using condoms, screening blood before transfusion, and bottle-feeding babies of infected mothers. There is no vaccine.

• TMV is a plant pathogen of plants such as tomatoes and tobacco.
• It discolours then leaves and destroys the cells so the plant cannot photosynthesise.
• TMV is spread by contact between diseased and healthy plants and by animal vectors.
• There is no treatment so farmers grow TMV-resistant strains of crops.
• It's spread can be reduced by good field hygeine and pest control.

• Bacterial diseases affect animals and plants.
• Antibiotics can be used to kill bacteria
• Some bacteria are becoming resistant to many antibodies

• Salmonella are bacteria that can be found in raw meat, poultry, eggs and egg products.
• The bacteria cause Salmonella food poisoning.
• Infection is spread by undercooked food or poor food hygeine.
• Symptoms are fever, abdominal cramps, vomiting, and diarrhoea.
• Prevention is by vaccinating chickens and good food hygeine, particularly keeping raw chicken away from food that is not going to be cooked.

• Gonorrhoea is a sexually transmitted disease (STD), or STI (sexually transmitted infection).
• STDs are spread by unprotected sexual contact with an infected person.
• Early symptoms are discharge from the penis or vagina and pain on urination.
• The disease may become symptomless and some people have no symptoms at all.
• Untreated gonorrhoea can lead to infertility, pelvic pain, and ectopic pregnancies. Babies born to infected mothers may have severe eye infections or blindness.
• Treatment is with antibiotics, but some strains of the bacteria are resistant.
• Prevention is by using condoms, limiting sexual partners,and treating all partners of an infected person with antibiotics.

• There are relatively few bacterial diseases of plants. Most are found in tropical and sub-tropical regions.
• Agrobacterium tumefaciens is a bacterium that causes crown galls.
• The galls contain a mass of unspecialised cells that are produced when the bacteria insert plasmids into the plant cells.
• The gall cells are new, undifferentiated, and genetically modified cells.
• Scientists can manipulate the bacteria by inserting desirable genes into the cell. These genes are then carried by the bacteria into the plant by natural processes. This results in genetic modification of the plant.

Fungi and protists are important pathogens.

There are only a few fungal diseases of humans. Athlete's foot is a well known example.

In plants, fungal diseases are common and can ruin whole crops.

Rose black spot is s fungal disease of rose leaves.

• Symptoms are purple or black spots on the leaves.
• The leaves turn yellow and rop early so there is less photosynthesis. This weakens the plant and it will not produce healthy flowers.
• The disease is spread when the fungus spores are carried by the wind. When the spores land on a plant they are spread by splashes of water when it rains.
• To reduce the spread of the fungus gardeners remove and burn affected leaves and stems. Fungicides are chemicals used to prevent the spread of black spot.
• Horticulturists have bred types of roses that are relatively resistant to black spot.

Protists are a type of single-celled organism. Some cause diseases.

Vectors are usually needed to transfer the protist to the host.

Malaria Is a disease caused by a parasitic protist that lives and feeds on other living  organisms.

• The protist is spread when a person is bitten by a female mosquito. The mosquito is the vector.
• The protists reproduce sexually and in the mosquite and asexually in the human body. 
• When a person is bitten, the protist enters the person's bloodstream and:
  • Is carried to the liver and then enters red blood cells.
  • Bursts out of the red blood cells, causing fever and shaking, and may cause death.
  • Is carried to another person after a mosquito bites an infected person (to obtain a meal of blood).

White blood cells in the immune system defend the body in three ways:

• They can ingest pathogens. Then they digest and destroy them.
• They produce antibodies to help destroy particular pathogens.
• They produce antitoxins to counteract the toxins (poisons) that pathogens produce.

The skin acts as a barrier by covering the tissues underneath. It also produces antimicrobial secretions to kill pathogenic bacteria, and heals quickly when cut because the blood clots and produces a scab.

The stomach produces acid, which kills pathogens in the mucus you have swallowed and in the food you eat

The respiratory system starts with the nose and continues with the trachea and bronchioles.

• Hairs and mucus in the nose trap pathogens and dirt particles.
• The trachea and bronchioles secrete mucus to trap pathogens. Cilia beaat to waft the mucus back up to the throat where it is swallowed