The virus causes different diseases in animals and plants.
Viral Disease in Animals
The virus does not produce symptoms directly in the animals (human). But it indirectly affects the host.
- Some virus stimulates the lysosome of the host cell to produce hydrolytic enzymes. These enzymes cause bursting of the host cell. These hydrolytic enzymes damage other cells.
- Sometimes, the envelope of the virus is toxic to the body of the host. It causes allergic reactions.
- In some cases, virus DNA incorporates in the DNA of the host. It stimulates the genes of host cells. Thus host cell starts dividing and produce tumors ( cancer).
In some cases Virus destroy the immune system of the host like ADIS. There are following animals viral diseases due to Viruses
1. AIDS ( Acquired Immuno deficiency syndrome ):
AIDS is caused by the HIV virus. The HIV virus affects helper T-lymphocytes ( a white blood cell ). T-Lymphocytes are a major component of the immune system. The increase in infection of HIV decreases the amount of T-lymphocytes. It fails in the immune system. So the infected person can be attacked by many diseases. HIV also infects the cell of the central nervous system ( brain or spinal cord ). Its symptoms are sudden weight loss, swollen lymph and general loss of immunity.
Some retroviruses have special genes called oncogenes. These viruses are called tumor viruses. These viruses inject these genes into the host cell. Thus diffusion starts in the host cell. It produced a tumor. The cell of this tumor may spread to another part of the body and cause cancer.
The inflammation of the liver is called hepatitis. It is caused by a viral infection. It has different types like Hepatitis A, B, C, D, etc. Its symptoms are jaundice, abdominal pain, Liver enlargement, Fatigue and sometimes fever. It may be mild. Sometimes it is acute and can cause liver cancer.
Poliomyelitis is caused by poliovirus. It is present all over the world. It occurs mostly in childhood. The poliovirus is the smallest know virus. It contains RNA in the spherical capsid. The poliovirus attacks a nervous system of children. It makes the children handicapped.
5. Influenza and Cold:
These are caused by influenza and cold virus. It is an enveloped RNA virus. Influenza and cold is a widespread disease. It occurs in epidemic form. Both these disease affects the respiratory tract.
6. Small Pox:
Smallpox is caused by poxviruses. It is a DNA enveloped virus. Smallpox was a common disease in the world before the early twentieth century. Raised vesicles are formed on the body. These vesicles are fluid-filled. Laters, these vesicles changes into pustules. These pustules later form pitted scars. These scars are called pocks.
7. Mumps and Measles:
Mumps and Measles viruses belong to group paramyxoviruses. They are large and RNA viruses.
8. Herpes Simplex
It Is caused by the Herpes virus. It is a DNA virus. It is a DNA virus. It is a naturally occurring disease of mankind. It forms vascular lesions within the epithelial layers of the ectodermal tissues. This disease occurs within the mouth on the lips and at other skin sites.