3 - infection and response

• Communicable diseases


  Diseases that can spread from person to person or between animals and people, caused by things like bacteria, viruses, parasites
• Non-communicable diseases


  Diseases that cannot spread between people or animals, generally last a long time and get worse slowly
• Diseases with weakened immune system

  Increased chance of suffering from communicable diseases
• Certain viral infections


  Can trigger some types of cancer
• Infection by pathogens


  Can trigger allergic reactions or worsen asthma symptoms
• Severe physical health problems

  Can trigger mental health issues like depression
• Other factors affecting health

  • Diet
  • Stress
  • Life situation
• Risk factors


  Things linked to an increased likelihood of developing a disease, but don't guarantee it
• Examples of risk factors

  • Lifestyle factors
  • Environmental factors
  • Substances in the body
• Many non-communicable diseases are caused by several different risk factors interacting
• Lifestyle factors


  Can have different impacts locally, nationally and globally
• Examples of risk factors that can directly cause disease

  • Smoking
  • Obesity
  • Alcohol
• Correlation between risk factors and disease doesn't always equal direct causation
• Non-communicable diseases have a high human and financial cost
• Diet is heavily linked to an increased chance of cardiovascular disease, but they can't cause the disease directly. It's the resulting high blood pressure and high bad cholesterol levels that can actually cause it.
• Non-Communicable Diseases


  Diseases that are not transmissible from person to person
• The human cost of non-communicable diseases is obvious. Tens of millions of people around the world die from non-communicable diseases per year. People with these diseases may have a lower quality of life or a shorter lifespan. This not only affects the sufferers themselves, but their loved ones too.
• The cost to the NHS of researching and treating these diseases is huge, and it's the same for other health services and organisations around the world. Families may have to move or adapt their home to help a family member with a disease, which can be costly. Also, if the family member with the disease has to give up work or dies, the family's income may be reduced. A reduction in the number of people able to work can also affect a country's economy.
• Cancer


  Uncontrolled cell growth and division resulting in the formation of a tumour
• Types of tumours


  • Benign - Grows until there's no more room, usually within a membrane, not normally dangerous
  • Malignant - Grows and spreads to neighbouring healthy tissues, cells can break off and spread to other parts of the body, dangerous and can be fatal
• Having risk factors doesn't mean that you'll definitely get cancer. It just means that you're at an increased risk of developing the disease. Cancer survival rates have increased due to medical advances such as improved treatment, being able to diagnose cancer earlier and increased screening for the disease.
• Lifestyle risk factors for cancer

  • Smoking - linked to lung, mouth, bowel, stomach and cervical cancer
  • Obesity - linked to bowel, liver and kidney cancer, second biggest preventable cause after smoking
  • UV exposure - increases chance of skin cancer, people in sunny climates, who spend time outside, and who use sun beds are at higher risk
  • Viral infection - infection with hepatitis B and C can increase risk of liver cancer, depends on lifestyle factors like unprotected sex and sharing needles
• Sometimes you can inherit faulty genes that make you more susceptible to cancer, for example mutations in the BRCA genes have been linked to an increased likelihood of developing breast and ovarian cancer.
• Semmelweis:

  • women dying from childbed fever after giving birth, but the cause was unknown
  • medical students went from autopsies to delivering babies without washing hands. women treated by these doctors were more likely to die
  • a doctor died from similar symptoms after cutting himself in an autopsy
  • washing hands reduced this, but other doctors resisted the theory
• pasteur showed microorganisms cause disease and developed vaccines
• lister used antiseptic chemicals to destroy pathogens before they caused infection in operating theatres
• microscopes improving showed that pathogens were really there
• hygiene prevents the spread of pathogens:

  • hand washing, especially after the toilet, before cooking and after contact with animals or infected people
  • use of disinfectants on work surfaces, toilets
  • keep raw meat away from food to be eaten uncooked
  • cough or sneeze into tissues and washing hands after
  • maintain hygiene of people and agricultural machinery to reduce plant disease spread
• infected individuals can be isolated to reduce spread
• destroy or control vectors
• vaccinate:

  • a small amount of a harmless form of a specific pathogen is introduced to the body, so if you come into contact with the live pathogen, you will not become ill because the immune system is prepared.
  • useful for protecting large populations against serious diseases, but it can't protect plants as they have no immune system
• in people, bacteria and viruses cause the majority of communicable diseases in people.
• in plants, viruses and fungi are the most common pathogens
• bacteria are single-celled living organisms that are much smaller then animal and plant cells
• viruses are smaller than bacteria and usually have regular shapes. they always cause disease in every type of organism
• bacteria divide rapidly by splitting in two by binary fission, producing toxins that affect the body and make you feel ill. they sometimes directly damage cells
• viruses take over cells, living and reproducing inside the cells to damage and destroy them
• symptoms of diseases are often high temperature, headaches and rashes because of the way the body responds to cell damage and pathogen toxins
• pathogens spread by air (including droplets):

  • bacteria, viruses and fungal spores are carried and spread between organisms through the air
  • when ill, you expel droplets with pathogens from breathing
  • flu, TB, cold
• direct contact:

  • common in plants
  • STDs eg. syphilis and chlamydia, HIV and hepatitis (also through cuts, scratches and needles)
  • animals can act as vectors