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  • Germs are tiny living things which cause disease.
  • They can only be seen with the aid of a microscope.
  • Germs are passed from one person to another through:
    • Direct Contact – This includes shaking of hands, hugging, using the same toothbrush, etc. Diseases caused by direct contact are called contagious diseases. E.g. Chicken pox, leprosy, measles, ringworm, smallpox, etc.
    • Air, Water, and Food – Germs can be carried by air to cause common cold or catarrh. Germs carried by water or food infect healthy people who eat or drink contaminated food or water. Diseases passed through air, water or food are called infectious diseases. Cholera is an example of an infectious disease caused by infected by food or water.
    • Through Vectors
      Characteristics of Vectors
      • They are small animals or insects.
      • They pass germs from one person to another.They are not infected by the germs they carry.
  • Female Anopheles Mosquito and Malaria
    • Malaria is caused by a bite from a female anopheles mosquito.
    • The life cycle of a female anopheles mosquito is:
      • Egg → Larva → Pupa → Adult
    • At the adult stage, it is said to have complete metamorphosis.

The Life Cycle of a Mosquito (Photo Credit: Epa.Gov)

Control of Mosquito and Malaria
    • Reduce mosquito breeding sites by clearing gullies and drying stagnant pools.
    • Use insecticides to kill adult mosquitoes.
    • Cover stagnant water with kerosene to kill larvae or pupa of mosquitoes.
    • Use mosquito-treated nets to prevent mosquito bites.
    • Treat malaria patients promptly.
    • Use malaria-preventive drugs as prescribed by the doctor.
  • Black Fly and River Blindness
    • A bite from a black fly causes river blindness.
    • The life cycle of a black fly is:
      • Egg → Larva → Pupa → Adult
    • At the adult stage, the metamorphosis is said to be complete.

The Life Cycle of a Black Fly (Photo Credit: Purdue.Edu)

Control of Black Fly
    • Chemicals are sprayed in streams to kill black flies.
    • Insecticides are used to kill the adult black flies.
    • Treat patients promptly with drugs.
  • Tsetse Fly and Sleeping Sickness 
    • A bite from a tsetse fly causes sleeping sickness.
    • The life cycle of a tsetse fly is:
      • Egg → Larva → Pupa → Adult
    • At the adult stage, it is said to have completed metamorphosis.

The Life Cycle of a Tsetse Fly (Photo Credit: TseTse.Org)

Control of Tsetse Fly and Sleeping Sickness
    • Use of insecticides to kill adult tsetse flies.
    • Treat sleeping sickness patients immediately.
  • Water-borne diseases are diseases caused by the intake of contaminated water.
  • They include:
    • Cholera – This is caused by eating food or drinking water contaminated by stool. It is treated with antibiotics.
      • Symptoms include frequent stooling and dehydration.
      • Ways of prevention include:
        • Immunization.
        • Boiling water before drinking.
        • Eat hygienically prepared food.
    • Diarrhea – This is caused by over-eating, viral/bacterial infection of food and water, anxiety, stress, allergy to certain foods, food poisoning.
      • Symptoms include:
        • Cramps.
        • Abdominal pains.
        • Nausea.
        • Stooling.
        • Dehydration.
      • It is prevented by drinking boiled water and eating hygienically prepared food.
    • Typhoid Fever – This is caused by bacteria. It is spread by eating food or drinking water contaminated by bacteria passed in stool.
      • Symptoms include:
        • Headache.
        • Stooling.
        • Constipation.
      • It is prevented by immunization, drinking boiled water, and eating hygienically prepared food.
Sources of Clean Water
  • Pipe-borne water.
  • Spring water.
  • Rain water.
Water Treatment Process
  • Filtration.

    An Example of Filtration (Photo Credit: Pinterest.com)

  • Boiling.

    An Example of Boiling (Photo Credit: Wired.com)

  • Flocculation.

    An Example of Flocculation (Photo Credit: Open.edu)

  • Distillation.

    An Example of Distillation (Photo Credit: Ctc-n.org)

  • The white blood cells in human blood defend the body against infection.
  • When germs enter the body, white blood cells produce antibodies which fight against the germs.
  • These antibodies give the body immunity (resistance) against future attack.
  • Immunization is the artificial inducement of immunity against a disease.
  • It is normally done by injection or oral application.
  • In Nigeria, children are immunized against measles, tuberculosis, tetanus, yellow fever, whooping cough, and diarrhea.
Type of Vaccine To Prevent
BCG Tuberculosis
DPT Diphtheria, whooping cough, tetanus
Oral polio vaccine Polio
Measles vaccine Measles
Tetanus vaccine Tetanus
  • Immunization of a child begins during pregnancy when the pregnant mother is given tetanus toxoid vaccine at the antenatal clinic.