infectious diseases

• Communicable diseases

  Diseases that can be spread from person to person (e.g. measles)
• Non-communicable diseases


  Diseases that cannot be passed from person to person (e.g. coronary heart disease)
• Communicable diseases are spread by pathogens such as bacteria or viruses
• People with a defective immune system (e.g. those with HIV)

  Are much more likely to suffer from infectious diseases (e.g. tuberculosis)
• Infection with the human papilloma virus (HPV)


  Can cause cervical cancer
• Infection with a pathogen

  Can trigger an allergic reaction (e.g. certain cases of asthma or dermatitis)
• A physical illness (e.g. arthritis)


  Can trigger a mental illness (e.g. depression)
• Ill health can be caused by both communicable and non-communicable diseases, poor diet, high levels of stress, and other life situations
• Health is defined as the state of physical and mental well-being
• Pathogen

  Microorganisms that cause infectious disease
• Types of pathogens

  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  • Reproduce very rapidly under ideal conditions
  • Can divide every 20 minutes
  • Release harmful chemicals called toxins that damage tissues and make us feel ill
• Viruses

  • Cannot be produced by themselves
  • Can only reproduce inside a host cell
  • Invade host cell, reproduce inside, then cause the cell to burst open and die
• Ways pathogens are spread

  • Airborne (e.g. influenza)
  • Waterborne (e.g. cholera)
  • Direct contact (e.g. HIV)
• Reducing the spread of pathogens

  1. Practicing basic hygiene (e.g. handwashing)

  2. Providing clean drinking water

  3. Reducing direct contact between individuals (e.g. using condoms)

  4. Isolating highly infectious patients

  5. Vaccination
• Around 300,000 people in the UK get food poisoning from a type of bacteria every year
• Many bacterial diseases can kill us
• Viruses are very damaging to host cells, causing them to burst open and die
• Viruses


  Pathogens that cannot be killed by antibiotics
• Measles


  • Highly infectious disease
  • First symptom is fever
  • After 3 days, develops red skin rash
  • Virus spread through coughing/sneezing droplets
  • Can cause complications and be fatal
• HIV

  • First symptom is flu-like illness
  • Virus attacks immune system cells
  • Immune system becomes severely damaged
  • Patient can contract other infections and develop cancer
  • Treated with antiretroviral drugs that stop virus multiplying
  • Not a cure, patient must take drugs for life
  • Transmitted through exchange of bodily fluids
• Most children are vaccinated against measles when young
• Patients who take antiretroviral drugs for HIV do not go on to develop AIDS and can lead a normal life expectancy
• Communicable disease


  A disease that is passed from person to person by a pathogen
• Pathogen

  A microorganism that causes an infectious disease
• Bacteria can be killed by antibiotics, unlike viruses
• Salmonella food poisoning

  1. Ingesting infected food

  2. Bacteria secrete harmful toxins

  3. Symptoms: fever, abdominal cramps, vomiting, diarrhea
• In the UK, all chickens are vaccinated against Salmonella
• Gonorrhea


  A sexually transmitted disease (STD)
• Gonorrhea was easily treated with penicillin in the past, but now antibiotic-resistant strains are common
• Stopping the spread of gonorrhea

  1. Using condoms during sex

  2. Getting tested and treated with antibiotics if had unprotected sex
• Communicable disease


  A disease that is passed from person to person by a pathogen
• Pathogen

  A microorganism that causes an infectious disease
• Unlike viruses, bacteria can be killed by antibiotics
• Salmonella food poisoning

  A bacterial disease caused by ingesting infected food
• Malaria


  A very common disease in certain parts of the world that causes over 400,000 deaths every year
• Malaria

  • It is a communicable disease, meaning it is spread by a pathogen
  • The malaria pathogen is an example of a protist
• Salmonella bacteria are sometimes found in poultry such as chicken, but in the UK all chicken are vaccinated against Salmonella
• Life cycle of malaria pathogen

  1. Infected person is bitten by a mosquito

  2. Malaria pathogen passes into the mosquito

  3. Mosquito bites a different person and passes the malaria pathogen to them
• Gonorrhea


  A sexually transmitted bacterial disease