Beneficial Effects of Micro-organisms in Nature
(i) Bacteria in the large intestine of man synthesize the vitamin K that is needed.
(ii) Yeasts are used in baking and preparation of alcoholic drinks. Yeasts are an important source of vitamin B.
(iii) Some bacteria are used in curdling of milk, brewing of wine and in butter and cheese making.
(iv) It is used in the production of antibiotics e.g. penicillin from the mould called penicillium.
(v) Saprophytic micro-organisms decompose sewage into harmless inorganic compounds.
(vi) Most decomposers are micro-organisms and they help to maintain soil fertility.
(vii) Some bacteria living in the rumen of ruminants like sheep, goat, cattle help to digest cellulose in their food (grasses/vegetation).
(viii) Micro-organisms help in maintaining some cycles in nature e.g. the nitrogen cycle and carbon cycle. They also help in recycling phosphates and sulphate.
EVALUATION (POST YOUR ANSWERS IN THE BOX BELOW FOR DISCUSSION)
Name two beneficial microorganisms and state their benefits to man.
Harmful Effects of Micro-organisms
(i) Most diseases in animals and plants are caused by micro-organisms especially bacteria, viruses and protozoans.
(ii) Huge amounts of food are spoiled annually by saprophytic fungi and bacteria.
(iii) They also cause deterioration/damage to materials such as paper, wood, cotton, leather, etc.
(iv) Micro-organisms can also cause the death of plants and animals.
Disease-causing Micro-Organisms
Micro-organisms are spread through the following:
(i) Air: Dust and water droplets in our air contain micro-organisms such as polio virus, measles virus, pox virus, common cold virus, Pneumococci
(a bacteria), Pencillium (a fungus), etc.
(ii) Water: Bacteria found in water include Bacillus, Pseudomonas, Vibrio, Azotobacter, Coliform micro-organisms (e.g. Escherichia coli, Vibro cholerae, Salmonella typhi), etc. Blue-green algae found in water include Nostoc,Anabaena and Oscillatoria.Protists in water include Chlamydomonas, Euglena,Amoeba, etc. Algae include Spirogyra, Volvox. Fungi include moulds and mildews.
(iii) Food: Most micro-organisms in food get in through faeces, dirty utensils and equipment, unhygienic habits and vectors like flies and cockroaches. Examples are Shigella sp, Salmonella enteriditis, Aspergillus flavus, etc.
(iv) Animal vectors or carriers.
(v) Personal or direct skin contact with a sufferer.
Disease-causing micro-organisms can enter the body through body openings like the mouth, nose or reproductive opening, through wounds, through bites of other animals and through blood transfusions.
Some important diseases, their causative micro-organisms, mode of transmission, host and symptoms are outlined in the following tables.
Air-borne Diseases
| Disease | Causative organism | Mode of transmission | Host | Major symptoms | ||
| 1. | Common cold | Virus | Airborne | Man | High fever, headache running nose. | |
| 2. | Chicken pox | Pox virus | Airborne | Man | Itchy skin rash | |
| 3. | Measles | Paramyxo-virus | Airborne and close contact | Children | High fever, skin rashes, headache, head cold, cough, body pain. | |
| 4. | Pneumonia | Bacteria | Air | Man, birds, pigs, cows | High fever, difficult breathing and cough | |
| 5. | Tuberculosis | Myco bacterium tuberculosis (bacterium) | Airborne, food | Man, cow | Persistent dry cough and profuse sweating at night. | |
| 6. | Meningitis | Meningo coccus (Bacterium) | Airborne | Man | High fever, headache, vomiting and stiffness of the neck. |
Food and Water-borne Diseases
| Disease | Causative organism | Mode of transmission | Host | Major symptoms | ||
| 1. | Typhoid | Salmonella typhi (bacteria) | Contaminated food and water | Man | High temperature, followed by bloody diarrhea | |
| 2. | Cholera | Vibro cholerae (bacterium) | Food and water | Man | Vomiting and diarrhea | |
| 3. | Food poisoning | Salmonella sp. (bacteria) | Infected meat, Poultry, eggs, milk and contaminated food | Man | Diarrhea and vomiting | |
| 4. | Amoebic dysentery | Entamoeba histolytica (protozoan) | Contaminated food and water | Man | Abdominal pain, and diarrhoea | |
| 5. | Poliomyelitis (infantile paralysis) | Picornavirus (virus) | Infected food and water, direct contact | Children | High fever, headache nausea, fits and stiffness of limbs |
Vector-borne Diseases
| Disease | Causative organism | Mode of transmission | Host | Major symptoms | ||
| 1. | Malaria | Plasmodium sp. (protozoan) | Bite of infected female Anopheles mosquito | Man | High fever, shivering and sweating | |
| 2. | Sleeping sickness (Trypanosomiasis) | Trypanosom agambiense (protozoan) | Tsetse fly bite | Man and domestic animals | Fever, headache, sluggishness, drowsiness and un- controllable sleep | |
| 3. | Yellow fever | Arbovirus | Bite of infected Aedes mosquito | Man | High fever, headache, backache followed by low body temperature and jaundice | |
| 4. | Plague | Bacterium | Bite of infected Rat flea | Man | Shivering fever, cough and difficult breathing | |
| 5. | River blindness (onchocerciasis) | Onchocerca volvolus | Bite of infected black fly | Man | Severe headache, high fever and gradual blindness | |
Diseases Spread by Contacts
| Disease | Causative organism | Mode of transmission | Host | Major symptoms | ||
| 1. | Tinea versicolor | Dermatophytes | Direct skin contact | Man | Yellow patches on chest, neck, face and back | |
| 2. | Athlete’s foot | Fungi | Direct skin contact | Man | Itching, smelly patches between toes | |
| 3. | Gonorrhea | Neisseria gonorrhoea (bacterium) | Sexual intercourse | Man | Inflamed urethra burning sensation during urination and thick yellowish discharge in male. In females there may be pain during urination, redness around the urinary opening and vaginal discharge. | |
| 4. | Syphilis | Treponema pallidum (bacterium) | Sexual intercourse | Man | A small painless sore or chancre on the penis or vulva. Mild fever, skin rashes, mouth ulcers and aches in lymph node regions. It may lead to abortion, attack the brain and cause blindness and insanity | |
| 5. | AIDS | Human immunodeficiency virus (HIV) | Sexual intercourse, blood transfusion, infected sharp instruments, mother to unborn child | Man | Susceptibility to all microbial infections, high fever, loss of weight, chronic diarrhoea, skin rashes, wasting away of muscles. | |
EVALUATION (POST YOUR ANSWERS IN THE BOX BELOW FOR DISCUSSION)
- Mention two disease causing microbes, state the diseases caused, the host, the mode of transmission and the symptoms of the disease.
- How do microorganisms gain access into the body?
- Describe the stages involved in the growth of inoculated microorganisms (Graphical illustration is important).
- (a) What is a venereal disease? (b) Mention four venereal diseases (c) Outline five ways of controlling venereal diseases.
- Read up on Towards Better Health.
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