Discovery Of The Causal Agent Of Aids Biology Essay

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One of the World Health Organisations major function is international tracking and monitoring of human diseases. Disease monitoring and surveillance in developed and developing countries are carried out by institutions and agents of varying sizes and one such is Centers For Disease Control and prevention (CDC) in USA. CDC performs a lions share in international disease monitoring. Information and details of human diseases are fed to CDC by a wide reporting network where it is investigated in detail by epidemiologists, statisticians and data processers .This information is communicated to public health workers and scientists throughout the world by means of regular publications such as the weekly Morbidity and Mortality Weekly Report .

Between Oct 1980 and May 1981, an alert physician Dr Michael Gottlieb together with colleagues at three different hospitals in Los Angeles, became intrigued by a cluster of five young male patients , whose ages ranged from 29 to 36 years under their care. Two of them died and the remaining three were seriously ill. All of them were diagnosed as having a highly unusual form of pneumonia due to a parasite called Pneumocystis Carinii. Pneumocystis Carinii Pneumonia was previously associated with patients with severe immunosuppression only . In addition, all of them were infected with CytomegaloVirus (CMV) and had thrush ,allof which is characteristic of immunosuppressed patients. In three of the five who were tested had marked disturbances in their functional capacities of their immune system. Another striking feature was that all of them were sexually active homosexuals but none of them knew each other.

These observation were first reported in Morbidity and Mortality Weekly Report of the CDC on 5 June 1981. The 3 July issue had the report of 26 homosexual men, 20 from New York and 6 from California with a very uncommon tumor called Kaposi's sarcoma(KS) . These men were also found to be harboring CMV, thrush and PCP.

Thus, it was at the beginning of the 1980s that the relatively unremarkable few cases of homosexual male patients with unusual infections and tumours heralded in an epidemic of one of the most devastating of all diseases of humankind. Because of its striking effect of the suppression of the immune system of patients , it was named Acquired Immuno Deficiency Syndrome(AIDS).

Similar patterns emerged elsewhere in other countries in the developed world and developing countries as well. In developed countries it was found among homosexual men and persons who injected themselves intravenously with illicit drugs. In developing countries it was spread mainly by heterosexual contact and was common in female prostitutes.

DISCOVERY OF THE CAUSAL AGENT OF AIDS :

A few of the early possibilities under consideration as cause of AIDS were amyl nitrate, semen, cytomegalo virus and African Swine Fever Virus(ASFV). Two important scientific discoveries published a decade previously paved the way for the development of a technology that ultimately enabled the causative virus of AIDS to be isolated. First of such discovery in 1970 was that of an enzyme called reverse transcriptase, which was responsible for the formation of a deoxyribonucleic acid (DNA) copy from a ribonucleic acid (RNA) template, the reverse order of the accepted sequence in biology. This key discovery earned for its discoverers ,David Baltimore and Howard Temin ,the Nobel prize.

The second important discovery on the road to elucidating the cause of AIDS was made in the laboratory of Robert Gallo at the National Cancer Institute, Washington DC . In 1976, Gallo discovered a growth factor for mature T - lymphocytes which would permit these cells to grow in culture in the laboratory. With the ability now available to grow T - lymphocytes in culture came the discovery of a number of viruses which specifically infect lymphocytes(lymphotropic Viruses).

Thus, following these two important breakthroughs, first human retrovirus (viruses possessing the enzyme reverse transcriptase and belonging to the family retroviridae) was isolated from a patient with leukemia of mature T-lymphocytes. This virus was called by Gallo as Human T- Lymphotropic Virus I(HTLV-I).A second virus, HLTV-II,was isolated shortly thereafter from a patient with T -lymphocyte leukemia.

Another offshoot of these two discoveries was the finding of a group of viruses named thereafter as slow viruses(Lenti Virus) in the retroviridae family. These caused slow and prolonged disease and were responsible for degenerative diseases drawn out over years progressively leading to death.

In 1983,Dr Francoise Barre - Sinoussi together with Professor Luc Montagnier, the head of the Viral cancer unit of the Pasteur Institute ,published a paper in the journal Science describing the isolation of a retrovirus from a patient with lymphadenopathy syndrome ,one of the disease manifestations that precedes AIDS , and called it the LAV(Lymphadenopathy Virus). The following year, Robert Gallo and colleagues from the National Institute of Health,USA reported isolation of a retrovirus from AIDS patients and called it Human T cell Lymphotropic Virus -III(HTLV-III) . The virus was subsequently given the rather cumbersome name of HTLV-III/LAV to provide equal recognition to both scientific groups. To resolve this nomenclatural confusion, the intrenational Committee on Virus Nomenclature in 1986 decided on the generic name "Human Immunodeficiency Virus(HIV)".

THE ORIGINS OF AIDS :

The origins of this remarkable virus and its equally remarkable disease have fired imagination ever since it was first recognized due to the intense and unique social, political and human implications. As on now, the answers to both the origin of the disease as well as to the ancestry of the virus remain as unsolved as when the questions were first posed.

One of the earliest of these postulates holds that the disease is not a new disease but is rather one of the old endemic disease of Africa which has been silent or unrecognized. The earliest serum specimen retrieved from archived frozen material which was positive for HIV antibodies was taken from a patient in 1959 in the Democratic Republic of Congo. It is hardly likely that this virus could have circulated in man much before 1950s and still have been unrecognized.

The second postulated scenario holds that the human virus originated from monkey immunodeficiency virus(simian immunodeficiency virus/SIV). One would need to postulate some mechanism by which these viruses could have been transmitted from monkeys to humans. The postulated sequence of events with all these "hypotheses" thus relates mutations in monkey virus leading to infection of humans in Africa followed by the subsequent introduction into the Western world where its spread was accelerated by the sexual revolution and use of hollow bore needle.

THE UNIQUENESS OF AIDS :

The AIDS epidemic has in many ways been a humbling experience to medical science. AIDS has probably now become one of the most formidable of all diseases in human history. The four cardinal features which makes it unique are: It is infectious and transmissible from person to person, once infection occurs it follows an inexorable course and later to death, infected persons remain infectious for the rest of their lives, the total sum of people infected is constantly and progressively expanding .

The social, psychological and political dimensions of the disease compounded the terror generated by it. In western and third world countries it affected the marginalized and victimized segment of the society. This association of societal rejection together with a morbid dread of acquiring infection ,has given rise to unique feelings of revulsion and condemnation of victims of the disease. This has resulted in many issues in all spheres of life which are new to scientists, doctors, psychologists, social workers, theologians , ethicists ,legal experts and politicians.

THE AIDS VIRUS : HIV

An understanding of the general characteristics and morphology of viruses in general will enable us to understand the uniqueness of HIV.

The word Virus is derived from the Latin word meaning 'poison' and 'slimy material' . Viruses do not fall strictly in to the category of unicellular micro organisms as they do not possess a cellular organization. Even the simplest of micro organisms are cells enclosed within a cell wall ,containing both types of nucleic acid(Deoxy Ribonucleic Acid/DNA and Ribonucleic Acid/RNA),synthesizing their own macro molecular constituents and multiplying by binary fission. Viruses on the other hand do not have a cellular organization. They contain only one type of nucleic acid, either DNA or RNA. They are obligate intracellular parasites.

As a structural entity, the virus represents the simplest biological unit able to exist and to perpetuate itself by making copies of itself(replication).They are the smallest living agents. Given the structural simplicity, viruses have no capacity to generate their own energy requirements for various biochemical processes such as replication. The viruses make use of the host cell's machinery and biochemical facilities for their living . In other words ,viruses are nothing but a group of inert cells outside a living cell ; they are 'alive' only inside host cells.

From a molecular geneticist's point of view, virus is a biological entity that transmits genetic information between cells thus favoring mutations and genetic changes. The medical importance of viruses lies in their ability to cause a wide variety of human infections. Their resistance to antibiotics differentiates them from higher microbiological forms of life.

The broadest grouping of virus is the family. Viruses are classified into two main divisions depending upon the type of nucleic acid family they possess. Thus there could be riboviruses and deoxyriboviruses. One among the RNA viruses is Retroviridae Family. These are so named due to the presence of the unique enzyme - reverse transcriptase - which facilitates production of a DNA copy from an RNA genome. All members of the family possess this enzyme and all make DNA copies of their RNA genomes inside the cells that they parasitize. Retroviridae family has three subfamilies of which HIV belongs to the subfamily Lentivirinae (lenti = slow).

HIV is an enveloped virus about 90 to 120 nm in diameter. The cell membrane is

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