Some Important Modern Viral Diseases

1. Cancer or Carcinoma:

Despite the fact that virus causing cancer is yet to be identified, still cancer is considered like a viral disease because of typical viral symptoms like Hyperplasia & hypertrophy, are reported in cancer. Certain genes called proto-oncogenes (c-onc) are present in human cells, which are involved in normal cell function. Mutation of proto-oncogenes may give rise to oncogenes, which stimulate cell division leading to an uncontrolled growth of the cells causing cancer. All retoveiruses and some DNA containing viruses (such as poxvirus, adenovirus, Herpes virus, hepatitis-B virus etc.) possess oncogene (v.onc) in their genome. These viruses are potential cancer producing pathogens. Study of cancer is called Oncology. Temin and Baltimore's studies on Rous sarcoma virus [RSV] have provided new dimensions in the knowledge of cancer. RSV is RNA containing virus and RNA of RSV forms DNA inside host cell through reverse transcription or 'Teminism'. Newly formed DNA develops malignant tumours in host. Harmful tumor is called malignant tumours whereas tumours, which are not harmful, are termed as benign tumours. Are lethal in advanced stage.

2. Acquired Immunodeficiency Syndrome (AIDS):

AIDS is a viral disease in which our acquired immunity defense system is gradually shattered, and the patient dies of multiple infectious diseases. The first indication of AIDS disease came to light in USA in 1981 amongst a group of young homosexuals who were addicts of herion and other narcotics. Luc Montagnier (1983) and Robert Gallo (1984) discovered that a new type of retrovirus is the causative pathogen of AIDS. In 1986, The International Committee of virus Nomenclature (ICVN) named the AIDS virus as Human Immunodeficiency Virus (HIV).

Although AIDS is hardly a two and half decades old disease, it has spread virtually all over the world, becoming pandemic. According to the estimates of world Health Organization (WHO), about 52 million people in the world harbour HIV and thousands of new cases are detected every day. In India HIV infection was first detected in 1986 in some sex workers of Tamil Nadu. Since then, about 4 million cases have been detected and infection is fast spreading.

Structure of HIV:

HIV is a spherical, enveloped virus of about 90-120 nm diameter. Its genome consists of a single stranded RNA filament segmented into two identical filaments and associated with a 'reverse transcriptase enzyme'. Due to the presence of two identical filaments of RNA, HIV is considered to be 'diploid'. The envelope is comprised of a lipid bilayer derived from host cell membrane, and projecting, knob like glycoprotein spikes with pedicels formed of virus coded glycol-proteins (gp).

Pathogenesis and Symptoms:

The sentinels of our defense system are a type of white blood cells called lymphocytes. These cells are of different types to play different roles in acquired immunity. One type of lymphocytes called T₄(T_H) lymphocytes, play the crucial role in activation of other components of the immune system and production of antibodies. HIV attacks T₄ lymphocytes and destroy them. As a result the T₄ lymphocyte count in blood gradually diminishes (<>4 lymphocytes through several years ultimately leads to a full blown AIDS disease, during which a patient suffers from persistent fever and diarrhea, loss of appetite and weight, weakness and fatique, body pain, dry cough, white lesions in mouth and alimentary canal and warts upon anus and genitals. Eventually, the patient loses immunity and dies of multiple infectious diseases.

Transmission:

HIV is present in blood and other body fluids of infected persons. Hence it is transmitted from one to another person through activities involving exchange or transfer of body fluids. Thus, HIV is primarily transmitted through sexual activities. Unprotected sex, sharing of syringes and needles by intravenous drug addicts, use of unsterilized syringes by doctors and health workers etc. are responsible for transmission of HIV. Transfusion of infected blood and blood products, transplantations from infected to healthy one through breast milk feeding after birth are the other potential mode of transmission of HIV.

Diagnosis:

Some genes of HIV genome code for synthesis of some antigens which are released into the blood by infected T₄ lymphocytes. The immune system of body produces antibodies against these antigens, which can be detected by serological test called Elisa (Enzyme Linked Immunosorbent Assay), western blotting and PCR polymerase reaction test are the confirmatory test.

Symbol used to describe AIDS disease is ' ' (red ribbon). Noted Hollywood star Rock Hudson & Lawn Tennis Player Arthur Ashe of US were notable AIDS-causalities.

NARI (National AIDS Research Institute Puna).

NACO (National AIDS Control Organisation).

ARV (Anti Retro Viral Drug).

Prevention and Treatment:

General precautions such as safer sex and extensive use of condoms, strict screening of blood and blood products used for transfusions and tissue and organ transplantations, and extensive health education can prevent AIDS. December, 1 is observed as World's AIDS Day to arouse general awareness amongst people about HIV infection.

At present, there is no effective drug to save the immune system of AIDS patient from collapse. However, there are some drugs which are known to delay the progress of AIDS. These include Zidovudine (Azidothymidine-AZT), XQ-9302, Amphotericine-B and its methyl ester etc.

3. Pox:

Following types of pox diseases are reported in man:

Small Pox : Caused by DNA containing Pox viridae, Varoila.

Chicken Pox : Caused by DNA containing Herpes Virus, Vacicella.

German Pox : Caused by RNA containing Para influenza virus, Rubella.

Measles or Khasra : Caused by RNA containing Para influenza virus or Paramyxoviridae with minus strand RNA. AS already mentioned, vaccines of small pox were prepared by Jenner. Earlier small pox was very lethal disease in epidemic form in India. Officially, it has been eradicated from India with the help of WHO