Infectious Diseases in Humans

• A disease is a condition that causes your body to function less effectively.
• A disease produces specific signs or symptoms, for example, fever, coughing and weight loss.
• Types of diseases

  • Infectious diseases
  • Non-infectious diseases
• Infectious diseases

  • Also known as transmissible diseases that can be spread from person to person
  • Caused by pathogens
• Pathogen

  A microorganism that causes a disease
• Common pathogens

  • Bacteria
  • Viruses
• Infectious diseases

  • Influenza
  • HIV
  • Pneumococcal disease
• Non-infectious diseases


  • Cannot spread from person to person
  • Not caused by pathogens
  • May be inherited or caused by factors such as malnutrition, lifestyle choices or environmental factors like pollution
• Non-infectious diseases

  • Liver cirrhosis due to excessive alcohol consumption
  • Type 2 diabetes due to unhealthy lifestyle
  • Coronary heart disease due to unhealthy diet or smoking
• Ways infectious diseases can be spread

  1. Through droplets in the air

  2. By direct contact

  3. By contaminated food and water
• Through droplets in the air


  • Pathogens in droplets can be expelled into the air when an infected person coughs, sneezes or talks
• Diseases transmitted through droplets

  • COVID-19
  • Influenza
• By direct contact

  • Infectious diseases can be spread by direct contact through sexual contact during intercourse or non-sexual contact, such as breastfeeding, shaking hands or touching contaminated surfaces
• Diseases transmitted by direct contact

  • HIV
  • Hepatitis B
  • Syphilis
• By contaminated food and water


  • Dirty water or unhygienic food preparation can lead to contamination of water or food with pathogens
• Diseases spread through contaminated food or water

  • Cholera
• Influenza

  A disease that attacks the respiratory system
• Influenza

  • Most people can recover quickly, but it can result in complications such as pneumonia
• Pneumococcal disease


  A disease that can cause infection in different parts of the body, including middle ear infection, lung infection (pneumonia), inflammation of brain and spinal cord membranes, and blood infection
• Signs and symptoms of Influenza

  • High fever
  • Stuffy nose
  • Headache
  • Cough
  • Sore throat
  • Muscle aches
• Signs and symptoms of Pneumococcal disease


  • Fever
  • Headache
  • Vomiting
  • Cough
  • Chest pain
  • Rapid breathing
• Methods to reduce transmission

  • Maintain a safe distance from an infected person
  • Cover mouth and nose when coughing or sneezing
  • Wear a mask when unwell
  • Wash hands with soap and water or use disinfectant
  • Avoid touching eyes, nose and mouth
  • Get influenza vaccination
  • Take prescribed antiviral drugs
  • Get the pneumococcal vaccination
  • Take prescribed antibiotics
• Vaccine

  A vaccine contains an agent that resembles a pathogen and prevents infectious diseases by stimulating white blood cells to quickly produce antibodies when the pathogen invades
• Vaccination

  The process of receiving a vaccine
• Vaccination helps make people become immune to a certain disease.
• How a vaccine works

  • A vaccine contains an agent that resembles a pathogen
  • White blood cells identify their antigens and produce specific antibodies
  • Some white blood cells remain in the bloodstream for a period of time
• Antibodies are specific in action.
• Antibodies have the ability to mark a pathogen for destruction by other types of white blood cells in the body.
• Some specific antibody-producing white blood cells may not remain in the bloodstream for a very long time.
• A booster shot of the particular vaccine may be necessary for individuals to effectively combat infections.
• Many people are compulsory to be vaccinated against serious infectious diseases like measles and diphtheria.
• When a large number of people are vaccinated

  Fewer people will be easily infected with the disease
• Fewer people being infected

  Reduces the spread of the disease
• Antibiotics are drugs used to treat bacterial infections.
• How antibiotics work

  Interfering with their growth and metabolic activities of the bacteria
• Antibiotics destroy bacteria.
• Actions of antibiotics

  • Inhibits synthesis of bacterial cell wall
  • Inhibits cell membrane function
  • Inhibits protein synthesis in ribosomes
  • Inhibits enzyme action in cytoplasm
• Viruses do not have cell wall, cell membrane, cytoplasm, and organelles such as ribosomes.
• Antibiotic resistance

  The ability of bacteria to resist the effects of antibiotics that were once effective in treating bacterial infections.
• Completing the recommended course of antibiotics increases the likelihood of killing all bacterial cells in a bacterial infection.