free booknotes online
PinkMonkey Online Study Guide-Biology

Pathogenic nature of virus

Viruses are causative agents of various dreadful diseases in plants, domesticated animals and man. A number of plants like tomato, tobacco, potato, sugarcane, etc. are affected and destroyed every year by viruses. Many domesticated animals are also destroyed. The common mammalian viral diseases are foot-and-mouth diseases of cattle, encephalomyeletis of horse, distemper of dog, rabies, etc.

Common human diseases caused by viruses are mumps, measles, chicken pox, small pox, herpes, influenza, common cold, jaundice, polio, etc.

Figure 14.6 Pathogenic human viruses

Viruses and cancer

Cancer is an uncontrollable and unorganized growth of cells causing malignant tumors, the cells of which have the capacity to spread indiscriminately anywhere in the body. Cancers grow by progressive infiltration, destruction and penetration of the surrounding tissues. It is curable in the initial stage but in the last stage called metastasia, the tumors break apart and the cells spread to other organs, the functions of which get disrupted, hence causing death of an individual. In the past it was thought that cancer was not caused by viruses, but in recent years, there have been increasing evidences to prove that the cancer is caused by the DNA virus called simian virus (SV-40) and a group of RNA viruses called retroviruses. The cancer causing-viruses are also called oncogenic viruses. Cancer can be cured in its initial stages by radiation, chemotherapy and surgery. Early diagnosis greatly decrease the hazards of cancer. It is believed that viruses are involved in leukemia, sarcomas and some kinds of breast cancer.

Virus and Aids

AIDS (Acquired Immune Deficiency Syndrome) is a recently discovered sexually transmitted viral disease. It is caused by Human Immuno Deficiency Virus (HIV), the target cell of which is T4 lymphocyte of the host, which usually forms the main line of defense. Due to failure of the human immune system, sufficient antibodies are not formed and the human body becomes susceptible to various infections. The disease is transmitted during blood transfusion, through sexual contact, from infected mother to the child during pregnancy or through breast feeding . There is currently no cure for AIDS. The treatment of AIDS, therefore, depends upon the efforts to check the secondary opportunistic infections attacking AIDS patients, as well as slowing or halting replication of the HIV virus.

Table of Contents

14.0 Introduction
14.1 Kingdom : Monera
14.2 Kingdom : Protista
14.3 Kingdom : Plantae
14.4 Kingdom : Fungi

Chapter 15


All Contents Copyright ©
All rights reserved. Further Distribution Is Strictly Prohibited.

About Us
 | Advertising | Contact Us | Privacy Policy | Home Page
This page was last updated: 5/9/2017 8:55:31 AM