Some viral diseases of human beings are as follows:

1. Influenza: It is caused by Myxovirus influenza, which travels in air and is transmitted from one person to another via sneezing, talking or coughing. Symptoms of influenza are discharge from the nose, sneezing, headaches, coughing and muscular pain. It can be prevented by avoiding contact with the infected person.

2. Jaundice/Hepatitis: It is caused by viral infection of HAV (in case of hepatitis A) and HBV (in case hepatitis B). HAV spreads via ingestion of contaminated food, water and milk, whereas HAB spreads by infected blood and from the mother to her babies. Hepatitis A causes symptoms such as high temperature, headache, fatigue, discharge of dark yellow urine and appearance of rashes on the body. Main symptoms of Hepatitis B include progressive liver disease, chronic active hepatitis and hepatocellular carcinoma.

Hepatitis A can be prevented by improving personal hygiene.

Hepatitis B vaccine can prevent the disease.

3. Rabies: It is caused by Lyssavirus, which spreads via the bite of an infected dog. It causes high fever, painful muscle contraction, restlessness, excessive salivation and hydrophobia.

It can be prevented by immunisation of stray dogs. To treat rabies, Pasteur's treatment is given to the patient.

4. AIDS: It is caused by a retrovirus known as human immuno-deficiency virus. HIV infects the host body by attacking at the WBCs, thereby weakening the body's self defence or immune system.

AIDS is transmitted from one person to another by the following methods:

(i) Unprotected sexual contact with the infected person.

(ii) Transfusion of blood contaminated by HIV.

Prevention of AIDS:

(i) Avoiding sexual contact with an unknown person.

(ii) Using sterilised needles for injections.

5. Polio: It is caused by polio virus, which enters the body via food and water. It destroys motor nerve cells of the spinal cord responsible for muscle control. Its symptoms include fever, vomiting, muscular pain and tingling sensation in limbs; these ultimately lead to paralysis.

Polio can be prevented by giving a child oral polio vaccine.