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Chapter: 11th 12th standard bio zoology Human Body higher secondary school

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Viral Diseases

Viruses have been identified as one of the causative agents for cancer or tumour. Such tumour inducing viruses are called oncogenic viruses.

Viral Diseases:


A. Cancer and Viruses:

 

Viruses have been identified as one of the causative agents for cancer or tumour. Such tumour inducing viruses are called oncogenic viruses. Adenoviruses, polioma virus, simian virus 40 (SV 40), Epstein-Barr virus (EBV) ( a herpes virus) are oncogenic DNA viruses. The RNA sar-coma viruses are oncogenic RNA viruses (eg., Rous sarcoma).

 

B. Rabies Virus and Rabies disease:

 

Rabies virus belongs to the rhabdovirus family. It is a parasite of domestic and wild mammals. The transmission to humans occurs through the bite of an infected animal. Dogs, cats, bats, are the mammalian animal sources for the rabies virus.

 

In humans, the symptoms of rabies are severe headache, high fever, alternating excitement and depression, muscular spasms in throat and chest, hydrophobia etc. The incubation time in humans is usually about 3 to 8 weeks but it may also vary. If untreated the mortality rate from rabies is 100 percent.

 

The new rabies vaccine was discovered in 1980. It is an inactivated vaccine prepared from the virus propagated in cultures of diploid human cells. This vaccine is both safe and highly immunogenic.

 

C. Pox virus:

 

Pox viruses are the largest of all viruses and are brick shaped. They contain double stranded DNA, protein and lipid. They have a dum bell shaped nucleoid surrounded by two membrane layers.

 

Variola virus is called the small pox virus. It is transmitted by droplet infection either directly from the infected person or by handling articles infected by the patient. Small pox is completely eradicated. The small pox vaccine consists of vaccinia, closely related to variola. It gives protection both by humoral and cell mediated immunity.

 

Other pox viruses are chicken pox and measles viruses.


D. Hepatitis-B:

 

Hepatitis B virus (HBV) is an enveloped virus with a double stranded DNA. This causes jaundice and hepatic carcinoma. This disease is deadly and more infective than AIDS. HBV vaccine consists of purified HBV Ag (Australian antigen) obtained from the blood serum of apparently healthy carriers.

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