Diseases Caused by Viruses


  1. Small Pox:


It is caused by poxviruses. This virus is DNAenveloped.


This disease occurred as epidemic in China in 12th century B.C. Until the early 20th century, it was common.

Symptoms / Effects:

This disease results in the formation of raisedfluid-filledvesicles on the body. These become pustules later on and form pitted scars, the pocks.


By 1950’s immunization and other measures had decreased the disease. However it is still present in the third world countries where many people are affected.

  1. Herpes Simplex


It is caused by Herpes virus (DNA virus). It is naturally occurring disease of mankind

Symptoms / Effects:

This disease most occurs in the mouth, on the lips, and at other skin sites.

In this disease vascular lesions are formed in the epithelial layers of ectodermal tissues

  1. Influenza


Influenza viruses are enveloped RNA viruses.

Epidemic Disease:

It is very common in man and occurs in epidemic form.

  1. Mumps and Measles


Mumps and Measles viruses belong to group paramyxoviruses. They are large, enveloped, RNA viruses.


It is highly contagious (communicable), wide spread, but rarely fatal. About 60% of adults are immune to it.

Measles is a common disease among children and adults all over the world. This disease develops immunity in its victim.

  1. Polio


Poliomyelitis is caused by polio virus. It is the smallest known virus. It contains RNA in spherical capsid.


It is present all over the world. It occurs mostly in children. The age at which primary infection occurs depends upon social and economic factors.

  1. Acquired Immuno Deficiency Syndrome(Aids)


The AIDS was reported by some physicians in early 1980’s in the young males. All these young patients were homosexuals.

This disease was also discovered in non-homosexual patients who were given blood (blood transfusion) or blood products.

In 1984 the agent causing the disease was identified by research teams from Pasteur Institute in France and National Institute of health in USA.

In 1986 the virus was named as human immunodeficiency virus (HIV).


The patient has complex symptoms such as severe pneumonia, a rare vascular cancer, sudden weight loss, swollen lymph nodes and general loss of immune system.


The major cell infected by HIV is the helper T-lymphocyte. It is the major part of the immune system.

The decrease of helper T-lymphocytes results in failure of the immune system. Now the Infected person is susceptible to other diseases. Cells of central nervous system can, also be infected by HIV.

Host Specificity:

It has been found recently that HIV infect, and multiply in monkey but do not cause disease in them. It means that HIV is host specific.


The HIV is transmitted by:

(a) Sexual contact

(b) Contact with blood

(c) Breast feeding and

(d) Healthcare workers can also acquire HIV during professional activities.


Important preventive measure is avoiding the direct contact with HIV.

Intravenous injection of drugs with common syringes must be prevented.

Sterile needles/syringes and utensils must be used.


Now the vaccine against HIV has been formed and its experimental supply to huff started in early 2001 in South Africa.

  1. Hepatitis


It is an inflammation of the liver. It is usually caused by viral infection, toxic agents or drugs.


Following are symptoms:

(a) Jaundice

(b) Abdominal pain

(c) Liver enlargement

(d) Fatigue and

(e) Sometimes fever

It may be mild or can be sharp and can lead to liver cancer.


Following are different types of hepatitis:

(a) Hepatitis A:

It was formerly called infectious hepatitis.

Hepatitis A virus (HAV) is an RNA virus (non-enveloped).

The disease is mild, short term and less virulent.

It is transmitted by contact with feces from infected individuals.

Vaccine is available for HAV.

(b) Hepatitis B:

It is also called serum hepatitis B (HBV) is the second major form of hepatitis.


Hepatitis B virus (HBV) is a DNA virus.


It is very common in Asia, China, Philippines, Africa and the Middle East.


It is transmitted by the exchange of body fluids, for example blood serum, breast milk and saliva,

During birth it is transmitted from mother to child.

It is also transmitted by sexual contact.


During acute attacks of Hepatitis B different symptoms appear like fatigue, loss of appetite and jaundice.

Infected persons can recover completely and become immune to the virus.

People with chronic hepatitis infection are at the risk of liver damage.


Hepatitis can be controlled by:

  • Taking hygienic measures,
  • Vaccination (Genetically engineered vaccine is available for HBV), and
  • Screening of blood/organ/tissue of the donor.

(c) Hepatitis C:

It was formerly called non-A, non-B hepatitis.


Hepatitis C virus (HCV) is also RNA virus (enveloped)

Symptoms / Effects:

It causes infusion hepatitis, which is less severe than hepatitis A or hepatitis B. hepatitis C often leads to chronic liver disease.


Through blood, from mother to child during pregnancy and afterward and by sexual


Vaccine is not available for HCV.

(a) Hepatitis D:

It is also called as delta hepatitis.

(b) Hepatitis E:

HEV is transmitted through the feces of an infected person.

Halbur and coworker (2001) said that hepatitis E could be transmitted through pig.

(c) Hepatitis F and G:

Hepatitis F & G are caused by unidentified virus.


These are infectious proteins discovered in 1983. They contain the information that codes for their own replication.

All other organisms contain their genetic information in nucleic acid (DNA or RNA).


Prions are responsible for: mad cow infection and mysterious brain infection in man.


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