How a Virus Finds a Host sample essay
AIDS and the bird flu have raised concerns about virus attacks in the public eye. Infectious transfer of virus also very often causes the common cold. We are able to tolerate or overcome the vast majority of viruses, but some of them succeed in causing us to fall ill, even to the point of death. Not everyone responds to a virus epidemic in the same way: some overpower the pathogen, while others succumb.
A fundamental understanding of the nature of a virus can solve these apparent paradoxes; its mechanism of taking shelter in living tissue is also relevant. It is worth noting at the outset that viruses search for all forms of plants and animals as hosts. Each type of virus has a particular preference of host. A virus is versatile and can change form with ease.
Basic genetic structures and systems
A virus is a kind of bridge between a form of life and an inanimate object. All living things are made from permutations and combinations of four nucleic acids, adenine, cytosine, thymine, and guanine. Sequences of nucleic acids form genes. Genes are in turn banded together, to form chromosomes.
The nucleic acids are joined together by ribose sugars. The latter has one molecule of sugar absent. The structure is entwined in the form of double helix coils inside the nucleus of each living cells. The latter are grouped together in higher forms of life to form tissues and organs. The nucleic acid structure inside each nucleus is called Deoxyribonucleic acid or DNA.
DNA is used by life forms to produce Ribonucleic acids or RNA. RNA has ribose sugar with the oxygen molecule missing in DNA. RNA has just one strand of nucleic acids, as opposed to two in DNA. RNA has uracil instead of thymine. RNA moves out from the nucleus to the cytoplasm of living cells. RNA is used to produce proteins, which act as the materials of life forms. DNA and RNA physiology is at the heart of all life. It is a common system from unicellular life forms to human beings. Protein production by RNA and RNA production by DNA is the chemical basis of life. This is a process, which continues without ceasing from conception to death.
We are now ready to look at the nature and structure of a virus. A virus has a structure similar to RNA (Lewin, 744). However, the host DNA does not produce it. It also differs from RNA in that it may have a protective membrane made of protein.
A virus is a kind of imposter. It finds a way inside a cell and abuses the host’s DNA to produce proteins of its own. Since a virus has no DNA, it does not qualify as a life form in the strict sense. However, as it able to use host DNA to produce protein, and since it has the ability to replicate, it shares an essential property of living things.
The fine distinction between a virus and a living cell with a nucleus could remain in the academic domain, were it not for the deleterious ability of a virus to threaten well-being and indeed life itself. A mitigating factor is that a virus cannot survive on its own: it must take shelter within the nucleus of a living cell, and is entirely dependant on the host DNA.
Cat and mouse
Higher forms of life, such as human beings, do not surrender to virus attack without a fight, and they most often win. A virus enters a host through the medium of foreign living tissue. Bodily discharges such as sputum, blood, semen, and mucus are the most common agents of viral transfer between one living body and another. Transmission is routine if two members of a species are involved.
A virus may occasionally adapt from one genus, even an order, or a phylum to another. Thus, an avian virus can infect a mammal, even a human. It can jump from one bird to another almost inevitably. Viruses know that they cannot always hope to find a host of the same species in which they currently reside (Watson et all, 1016).
A virus is always on the search of a new host for its use of the present host’s DNA can be fatal for that host. The virus will have no use for a dead host, and must hence find a new life to infect. It has developed a great adaptive capability, and can adjust to the DNA of a new host, which may be an entirely different form of life in which it has existed before. A bird flu virus in a chicken would like a healthy chicken in which it can spread. Should other chickens be scarce, it will try to infect some other bird it can find.
It will settle for a human if it can find no bird or other animal. It is worth repeating that the bird flu virus can move from one bird to another bird or from one bird to a human, only through oral or nasal of anal discharge from the infected and original host. Should the latter be isolated, then the virus is doomed to extinction with the death of its host. Infection is essential for viral transfer.
Animal bodies, especially human beings have powerful and sophisticated systems to combat invading viruses. Should a human being touch and ingest some discharge from an infected host, the virus will gain physical entry, but the body, which it has entered, will not take things lying down. Defense systems in humans and other animals are equipped to detect that a rogue pretending to be RNA has entered the body and is trying to cheat the DNA to produce proteins for its own use.
A virus tries to read the nucleic acid sequence in the DNA of any host that it finds. It then attempts to produce proteins of its own need and choice from the DNA it encounters (Heritage, Evans and Killington, 122). We should bear in mind that a virus is essentially an imposter in the garb of RNA. It tries to adjust its RNA sequence in a manner such that the host DNA cannot see through the disguise.
Higher forms of animal life have defense cells in blood. Soldier cells try to capture foreign virus-loaded tissue as soon as it enters the host. These cells are called macrophages and they contain most invasions by literally swallowing the foreign bodies.
This mechanism is not necessarily comprehensive, and some particles of the foreign bodies may escape the macrophage confrontation. The sub-microscopic size of a virus means that a few members of an infectious source may escape the host body’s attention. Virus is then free to enter living cells of the host and start interaction with the DNA. The virus can tell instantly that it now has a different DNA structure. It starts studying the new nucleic acid sequence and sees it can replicate in the changed circumstances.
It is now time for the lymphocytes in the host blood to take charge (Despopoulos and Silbernagl, 68)
Lymphocytes are of two kinds, B and T. The latter specialize in fighting viruses. They recognize the production of unusual proteins, and detect the viral infection of cells. T lymphocytes kill cells infected by a virus, in a bid to contain the infection. T lymphocytes are produced in the thymus. Healthy individuals have immense capacity for defense and can ward off a majority of virus attacks.
A compromise often prevails with the T lymphocytes winning the fight against a virus, though it is unable to destroy all traces of the virus in the host. Such a host then functions as a carrier, living with a low intensity of virus attack without external symptoms of any medical condition. A carrier can infect another individual who may succumb to the virus if its T lymphocyte system does not function well. Cancers of the lymphatic system and malnutrition are the primary reason for a host’s T lymphocytes to fail in protecting a host from virus attack.
We must bear in mind, for the question that has prompted this document, that a virus does not have the luxury of choosing a host. It will take any available living cell and try to adjust to the DNA sequence it finds. Nature favors the host: the virus will generally fail to break the code, or will perish with the host cell whose code it has broken.
Though anti-retroviral therapy has now entered the realm of reality, nature provides hosts with the capability to recognize a virus and the will to destroy cells infected by viruses. Nature balances such powers by making viruses highly adaptable. They can quickly change their own sequences of acids in bids to escape detection and to survive. Viruses will also settle for sub-clinical situations in which they are able to survive without killing the host on which it depends.
It follows that immunity is a key to fighting viruses. Higher forms of life are equipped with innate capabilities to fight viruses to the extent that the species can thrive, though some proportion of every population falls prey. Hygiene and balanced nutrition are the only things that most life forms need to defeat thieving viruses.
Despopoulos, A and Silbernagl, S, Color Atlas of Physiology, Georg Thieme Verlag Stuttgart, 1991
Heritage, J. G. V. Evans, and R. A. Killington, Introductory Microbiology, Cambridge University Press, 1996
Lewin, B, Genes, Oxford University Press, 1997
Watson, J. D. Nancy H. Hopkins, Jeffrey W. Roberts. Joan A. Steitz and Alan M. Weiner, Molecular Biology of the Gene, The Benjamin/Cummings Publishing Company, Inc. (1998)
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