Infectious diseases

• Communicable diseases

  Diseases that can be spread from person to person
• Communicable diseases

  Spread by pathogens such as bacteria or viruses
• Non-communicable diseases

  Diseases that cannot be passed from person to person
• Diseases can cause ill health, which is defined as the state of physical and mental well-being
• Ill health can be caused by communicable and non-communicable diseases, poor diet, high levels of stress, and other life situations
• 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 allergy (e.g. certain cases of asthma or dermatitis)
• Physical illness (e.g. arthritis)

  Can trigger a mental illness (e.g. depression)
• 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 (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
  • Attacks immune system cells
  • Immune system becomes severely damaged
  • Can lead to other infections and cancer
  • Treated with antiretroviral drugs but not cured
  • Transmitted through exchange of bodily fluids
• Most children are vaccinated against measles when young
• Antiretroviral drugs stop HIV from multiplying and prevent AIDS development
• HIV can be spread through unprotected sex and sharing infected needles
• Communicable disease

  A disease that is passed from person to person by a pathogen
• Malaria is a very common disease in certain parts of the world and it causes over 400,000 deaths every year
• Malaria

  A communicable disease spread by a pathogen
• Malaria pathogen

  • An example of a protist
• Malaria is a very serious disease, people with malaria experience repeated bouts of fever and in some cases it can be fatal
• Life cycle of malaria

  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
• Mosquito

  A vector that carries a pathogen from one person to another person
• Preventing the spread of malaria

  1. Stop the vector (mosquito) from breeding

  2. Drain areas of still water where mosquitoes breed

  3. Spray areas of still water with insecticide

  4. Prevent mosquitoes from biting humans by using mosquito nets
• It is virtually impossible to kill all mosquitoes
• Nonspecific defense system

  The body's first line of defense against pathogens, preventing them from entering the body
• Parts of the nonspecific defense system

  • Skin
  • Nose and mucus
  • Trachea and bronchi (cilia)
  • Stomach (hydrochloric acid)
• Skin

  • Forms a protective layer covering the body
  • Outer layer of dead cells difficult for pathogens to penetrate
  • Produces sebum which can kill bacteria
  • Can scab over when damaged to prevent pathogen entry
• Nose and mucus


  • Contains hair and mucus to trap pathogens before they enter the breathing system
• Trachea and bronchi

  • Covered in tiny hair-like structures called cilia
  • Cilia are covered in mucus which traps and moves pathogens upwards towards the throat to be swallowed
• Stomach

  • Contains hydrochloric acid which kills pathogens before they can enter the digestive system further
• Even with the nonspecific defense systems, pathogens can still get into the human body and cause serious disease