What is disease?
A disease is a condition in which the health of an organism is damaged. Disease can be divided into four main types; disease cause by pathogens, deficiency diseases, hereditary diseases and physiological diseases.
A disease is an illness in a human, animal, or plant.
Distinguish among pathogenic, deficiency, hereditary and physiological disease
Pathogenic-is a parasitic organism which cause disease in its host. There are five group of pathogens; viruses, bacteria, fungi, protozoans and parasitic worms.
Pathogenic group | Characteristics | Diseases in humans | Diseases of crops |
Viruses | Minute ‘particles’ composes of nuclear material (DNA) enclosed in a protein coat. All are parasites which cannot reproduce outside living cells. Inhibit cellular activity and destroy cell structure. | Polio, influenza, measles, yellow fever, dengue, herpes, AIDS. | Mosaic disease of tobacco.Bunchy top of pawpaw.Ratoon stunting of sugar cane |
Deficiency disease-are caused by the shortage or lack of a particular nutrient in the diet.
Diseases | Cause | Symptoms | Control |
Anaemia | Deficiency of iron resulting in reduced hemoglobin production | Reduction in number of red blood cells, reduced O2 carrying capacity of blood, pale appearance | Eating iron rich foods, e.g. meat, liver, green leafy vegetables. |
Hereditary diseases-are passed on from one generation to the next by genes e.g. haemophilia, sickle cell disease. They cannot be cured.
Sickle cell disease
Sickle cell disease manifests itself onto two forms:
1.Sickle cell anaemia-instead of containing normal haemoglobin A (HBA), the person’s blood contains abnormal haemoglobin S (HBS) which crystallizes when the oxygen concentration drops, e.g. in capillaries and veins. This causes newly formed red blood cells to become sickle shaped. Sickle-shaped cells carry little oxygen and symptoms of severe anaemia develop. During childhood a series of painful ‘crises’ occur, characterized by...