Bacteriophages are viruses which infects live and reproduce in a bacteria cell like an Escnerichia coli.

• Stage A: Shows a virus approaching a bacterium.
•  Stage B: The virus attaches it cell to the bacterium.
• Stage C: In stage C, the DNA of the virus enters the bacterium leaving the empty protein coat and tackle on the outside of the bacterium.
• Stage D: The varium DNA now multiply rapidly within the bacterial cell and in a short time enough new virions are formed.
• Stage E: The viral DNA the acquires a new protein coat and boil and end is stage E forming mature viruses.
• Stage F: The bacterium new ruptures and the cell contains together with the mature viruses are discharged into the environment. Each virus can now attack a healthy bacterium.

COMMON VIRAL DISEASES OF MAN

1. AIDS ( Acquired Immune Deficiency Syndrome )

1. Causative agent: Human Immune Virus (HIV)
2. Method of spread:

-Through sexual intercourse with an infected person.

-Blood transfusion with blood from an infected person.

-Using or sharing infected blades, syringes, needles, etc.

-During pregnancy from an infected mother to the foetus or through breast milk.

3. Incubation period: Many years
4. Signs and symptoms: Loss of weight, persistent fever, prolonged dry cough, diarrhea, skin rashes, etc.
5. Prevention and control:

-Abstinence from sexual intercourse

-Males and females should use condoms, during sexual inter course with suspected partners.

-Avoid sexual promiscuity.

-Blood should be screened before transfusion.

-Avoid sharing blades, needles, syringes.

-Infected pregnant women should take drugs which will prevent the transmission of the virus to the foetus.

2. Poliomyelitis

1. Causative agent: Polio virus.
2. Method of spread: Water and food borne.
3. Incubation period: 7-12 days.
4. Signs and symptoms: Fever, headache, stiffness of the neck and other muscles.
5. Prevention and control:

-Vaccination with the Salk or Sabin vaccine.

-Boil water for all purposes before use.

-Good food and personal hygiene.

3. Influenza

1. Causative agent: Haemophilus virus
2. Method of spread: Airborne
3. Incubation period: 1-3 days
4. Signs and symptoms: Headache, fever, loss of appetite, weakness and general pains.
5. Prevention and control:

-Vaccination

-Avoid overcrowding.

-Good ventilation.

4. Measles

1. Causative agent: Marbillo virus.
2. Method of spread: Airborne
3. Signs and symptoms: Sore throat, running nose, watery eyes, cough and fever, small white spot appears inside the mouth on wall of cheek. Two days later, a reddish rash appears on neck and behind ear, spreading over the rest of the body.
4. Prevention and control:

-Giving life attenuated vaccines.

-Good ventilation.

-Isolation of patient and avoiding of overcrowding in school.

ECONOMIC IMPORTANCES OF VIRUSES

1. Harmful Effects

-Causes diseases to man. Eg: poliomyelitis, AIDS, etc.

-Destroy plants some of which are economically important.

2. Useful Effects

-Used in research to produce vaccines. Eg: the vaccine against poliomyelitis.

-Some attack and destroy diseases causing bacteria

-Used for biological control.

-Used for genetic engineering.