Viruses-Discovery/HIV-AIDS VIRUS

Introduction

Viruses are extremely small organisms. They are even smaller than bacteria. You know that you cannot see bacteria with your naked eyes. You can see bacteria with an optical microscope but you cannot see virus with optical microscope. There is a kind of microscope called electron microscope, it uses electron beam instead of light. With will learn how scientists came to know about the existence of viruses, their way of behaviour and why it is difficult to treat them. It is difficult to say you are given a particular kind of drug to someone suffering from a disease caused by viruses. Example is the HIV virus.

table of content

1. composition of the microbial world 
2. general characteristics of bacteria 
3. historical aspects of microbiology
4. a brief survey of microbes as friends and foes 
5. activities of living things
6. cell activities
7. fung and root
8. general characteristics of algae 
9. general characteristics of fungi 
10. general characteristics of viruses 
11. general structure, anatomy, physiology of the root and the leaf
12. microscope and specimen preparation 
13. prokaryotes and eukaryotes cells
14. the relevance and scope of microbiology 
15. the cell, its general structure and activities
16. the stem
17. viruses-discovery/hiv-aids virus

 Discovery of Virus

Some tobacco plants infected with mosaic disease were crushed, the juice was passed through a very fine filter. The filter was fine enough to trap bacteria. The filtrate which was supposed to be pure was applied to a healthy leaf of a healthy plant. The disease Mosaic was induced in the leaf. This baffled scientists, before this time they knew about bacteria and they knew that bacteria can be filtered using a very fine filter. It then means there are other disease causing organisms that are tinier than bacteria. Later on, you will discover that the diseases caused by viruses are different from diseases caused by bacteria. When you look at the

Characteristics of Viruses

Viruses can not be seen with the naked eye. Neither can they be seen with a light microscope because of their sizes. That is why they can pass through a very fine filter.  Take note of the place of viruses among the kingdom of living organisms. They are on their own. They do not have cell structure. They can not increase except by living inside another living cell. When an organism lives and depends on another organism for its activities, that organism is said to be a parasite. Viruses are parasites because they live in another living cells. While living in other living cells, they cause harm or what medical science refers to as disease. Viruses have very simple structure.

 Lif e Cycle of Virus

You have heard about HIV-AIDS, it is caused by a virus. Let us look at the way an HIV virus reproduce. Figure 4.2 this is the life cycle of a virus.

1. Virus approaches 
2. Virus glycoprotein attaches to a specific receptor protein in the cell surface membrane. 
3. Virus enters the cell by endocytosis. 
4. the viral RNA is released into the cytoplasm of the host cell, together with the enzyme reverse transcriptase. 
5.  A double-stranded DNA copy of the single-stranded virus RNA is made using reverse transcriptase. 
6. The DNA copy enter the nucleus and inserts itself into the host DNA. Whenever the cell divides, it also makes a copy of the viral DNA. Increasing the number of infected cells. 
7.  After a period of inactivity know as the lantency period, which lasts on average 5 years, the virus becomes active again. The stimulus for converting a latent virus into an active virus is poorly understood. 
8. New RNA is produced (transcription) and viral proteins are made using the host’s protein synthesizing machinery. 
9. New viral particles assemble. 
10. Virus particles bud off from the cell surface membrane of the host by exocytosis. 
11. The cell eventually dies as a result of the infection. 

HIV or human immune-deficiency virus is the virus that causes AIDS (Acquired Immune Deficiency Syndrome). The interesting thing about HIV virus is that it belongs to a group of RNA viruses known as Retroviruses. This name comes from the fact that these viruses can convert their RNA back into a DNA copy using an enzyme known as reverse transcriptase. Normally a section of DNA (a gene) is
copied to make RNA, a process called transcription, and the enzyme controlling it is called reverse transcriptase. The virus infects and destroys certain white blood cells called T. Helper Lymphocytes, thus crippling the immune system.

The Processes

1. Virus approaches a T4 lymphocyte cell. 
2. Virus glycoprotein attaches to a specific receptor protein in the cell surface membrane.
3. Virus enters the cell by endocytosis. 
4. The viral RNA is released into the cytoplasm of the host cell, together with the enzyme reverse transcriptase. (
5. A double stranded DNA copy of the single stranded virus RNA is made using reverse transcriptase. 
6. The DNA copy enters the- nucleus and inserts itself into the host DNA, Whenever the cell divides, it also makes a copy of the viral DNA, increasing the number of infected cells. 
7.  After a period of inactivity known as the latency period, which lasts on average of 5 years, the virus becomes active again. The stimulus for converting a latent virus into an active virus is poorly understood. 
8.  New RNA is produced (transcription) and viral proteins are made using the host's protein synthesizing machinery.
9.  New viral particles assemble.
10.  Virus particles bud off from the cell surface membrane of the host by exocytosis. 
11.  The cell eventually dies as a result of the infection. 

 Growth

The virus you saw earlier are not like bacteria. The way you will observe the growth of bacteria in a culture is different from that of the virus. Why can you not grow and observe virus in a culture? You learnt that they grow inside another cell not on their own. Scientists have been making use of this knowledge to culture viruses inside chick embryo. It is grown in petri dishes incubated in sterile room. The process is called cell culture.

HIV-AIDS VIRUS

AIDS- Acquired Im mune Deficiency Syndrome It is a disorder which damages the human body’s immune system. It is caused by the HIV (Human Immuno-deficiency Virus)

Transmission

When an individual, even animal (e.g. goat) is infected with virus, that person's or animal's surrounding is saturated with virus. When someone with flu sneezes, he releases trillions of viruses. Any healthy person around contacts the virus. There are three main routes of transmission.

1. Physical contact, through blood or semen, e.g. vaccinia virus in AIDS. 
2.  Axial droplets of virus bearing dust particles, e.g. respiratory viruses that cause common colds - influenza A, B and C. 
3. Faecal-oral transmission, e.g. polio virus and gastroenteritis. 

 Transmission of HIV

You have learnt about viruses. HIV is just an example of viruses. You learnt that HIV virus like any other virus cannot survive on its own, except in another cell or body fluid. HIV virus was discovered among homosexuals, it could also be transmitted in heterosexuals. The virus passes in the fluid of the affected person to the fluid of the unaffected person. Example is the semen, blood or for the
homosexuals, anal intercourse.


The linings of the anus are very fragile, the vessels break easily, and the semen therefore passes to the blood in the lining of the anus. Many people share needle, that is drug users or nurses who use the same needle for different people. AIDS can be contracted through needles. Many people contract AIDS through blood transfusion. If donor's blood is infected, the recipient contracts the disease. Close contact between infected and non-infected person, through open cuts, and open wounds is another avenue of transmission. Mothers pass on the virus to their babies through childbirth, through the placenta, or breastfeeding.

 Process of HIV Infection

Taylor et al (1998) gave five stages of HIV infection in the body, i.e. after infection. Stage I: After infection, most people remain symptom free for years, while some may develop symptoms like fever, reduction of T helper cells in the blood and skin rash. The body produces its own anti-bodies against HIV. This can be detected on examination. This stage is between two weeks to 3 months. The fact
that some one went for a test and it is negative is not an absence of the virus. It may take between two to ten years before the disease is full blown. When infection occurs, the body produces anti-HIV antibodies. It takes up to three months before antibodies are produced.

 HIV-AIDS Five Final Stages

1. Presence of HIV antibodies in the blood but T. helper cell number in the blood is normal. 
2.  Presence of HIV antibodies in the blood, T helper cell number in the blood is normal but chronic lymphadenopathy detected. 
3. HIV antibodies present, number of T helper cells in the blood decreases and chronic lymphadenopathy may be there. 
4. HIV antibodies present, number of T helper cells in the blood decreases and delayed type of hypersensitivity reaction (DTH) is also suppressed. 
5. HIV antibodies present, number of T helper cells in the body decreases, complete loss of delayed type of hypersensitivity (DTH) reaction and appearance of fungal infection in mouth. 

Treatment And Prevention of HIV- AIDS Virus

When one goes for test, essentially what is done is that a sample of blood is taken and mixed with HIV proteins already prepared for the purpose. The test is positive if the blood already has anti-HIV antibodies by binding to the viral proteins. Unlike bacteria, antibiotic cannot be used to treat HIV-AIDS due to the nature of the virus. What is the nature again? You were told that they live in cells of
organisms not on their own. For now, scientists (doctors) try to relieve the symptom on sufferers. Taylor et al gave three areas of research aimed prevention and treatment. They are: at

1.  Restoring, or improving the damaged immune system of victims. 
2. Developing drugs that will stop the growth of the virus and also treat the other infections and symptoms that result from HIV infection. 
3. Developing a vaccine against the virus. There are other infections (secondary) associated with HIV infection, 

 Drugs

Many retroviral drugs have been developed. These are Azidothymidine (AZT), Zalcitabine Glycyrrhizin and Ribavirin. The success of these drugs are still been determined. The best way to prevent the disease is to look at how the disease can be contracted and avoid them.

Sum mary

Virus is about 50 times smaller than bacteria, virus cannot carry out activities on its own like a cell. It lives in other living cells and thrives in such cells. It is non- cellular. Viruses do not have cell structure. They are difficult to culture even through they have been cultured in chick embryo. You have seen how the HIV virus can be transmitted. There is no known method of treatment yet, even though some drugs have been developed and are being tried. The best method so far is
prevention. Avoid all means of contracting the virus.