Viruses Essay, Research Paper
Today, our world is faced with many diseases. Some haven?t been discovered and some have no cures. The immune system fights off many of these diseases, but what happens when it fails us? One of the most deadly, incurable disease the world is faced with today is the Human Immunodeficency Virus (HIV). There is no none cure yet.
Viruses cause colds and the flu. Viruses are microscopic particles that invade the cells of plants, animals, fungi, and bacteria. They often destroy the cells they invade.
How do viruses reproduce? A virus first enters a cell in one of three ways: direct penetration, endocytosis, or membrane fusion. The virus takes over the cell?s machinery and is thus forced to make the virus?s proteins and RNA. When the virus has entered, viral RNA is released in to the cell and reverse transcriptase occurs. Reverse trancriptase is when the cell makes a DNA copy of the viral RNA. It then produces the proteins and genes the virus needs to be assemble. The virus can then be released by three ways: lytic, lysogenic, and persistent.
A virus, although not considered to be alive, does have a life cycle. First the virus attaches to a cell, which it recognizes by its surface markers. Then it penetrates the cell and gets inside. Next, it replicates and makes copies of itself. It then assembles itself back together and the new viruses are released.
A virus cannot replicate by itself; it has to infect a cell. The virus is always the same size. It doesn?t have a metabolism. A virus has three different shapes it can be: helical, polyhedral, and enveloped. It is made up of nucleic acid (RNA or DNA), and surrounded by a protein coat. Certain viruses can survive harsh conditions.
Pathogens, disease-causing agents, have to enter the body to cause illness. There are several ways for them to get into the body: through the genitals, breaks in the skin, and natural openings. The immune system usually stops these invaders from getting in.
The primary way to stop pathogens is by the skin. But, the skin has natural openings where they can get in. The eyes, ears, nose, mouth, and genitals are all natural openings.
The second line of defense is at these natural openings. The pathogens get stuck in the mucus lining of the nose and mouth or are killed by the saliva and stomach acids; tears from the eyes; earwax; and acidic secretion of the vagina all stop pathogens but they don?t get them all.
The third line of defense is the Tortiory Response. There are two different kinds, innate (which you are born with and is non-antigen specific and acquired (which you acquire through life and is antigen specific). Innate has three different reposes to it. The first: phagocytic cells eat live viruses, bacteria and, dead cells. The second: natural killer cells are non-specific and destroy all infected cells. The third: interferon binds to the surface of surrounding healthy cells and activates their genes to create an antiviral state. Acquired immunity has different parts to it: macrophages (ingest viruses and expresses information to other cells; intructs and recognizes), T4-cells (instruct), T8-cells (respond), B-lymphocytes (respond), and lymphokines (rate control). There are two different kinds of acquired immunity: humoral and cell mediated. The humoral response involves the production of antigen-specific antibodies. Those antibodies neutralize he virus, help macrophages ingest and T8-cells to destroy it, and cause the destruction of the viral envelope. Colonal selection is part of the humoral response. The T4-cells get the right B-cells and activate them. The B-cells produce antibodies quickly then start to divide. Once they divide, they are called plasma cells and are able to produce 2,000 antibodies per second for 4-5 days. The cell-mediated response develops T8-cells that destroy host cells that have been infected already. T8-cells can tell the difference between regular and infected cells.
HIV is a very deadly disease. There are certain risk behaviors associated with the disease. HIV is mainly transmitted by sexual contact or either by IV drug use. Anal sex carries a higher risk of getting it than vaginal or oral sex. The probability is 1/33 to 1/10 people. Vaginal intercourse also caries a high risk. Male to female the probability is 1/75 to 1/100 people. Female to male is 1/300 to 1/1000. The risk is higher for the female because HIV only infects cells that have the CD4 surface marker (semen has a lot of CD4 cells in it and there is not much blood flow in the vagina). Oral sex has a low risk but is still cacheable. Blood to blood contact is less and less likely now that tests exist that can check blood for the HIV antibodies. A tear in the placental wall and during childbirth (lots of blood) is the only blood to blood way that HIV can infect naturally (plus breast-feeding). The most recognized forms of blood contact are blood transfusions, shared, dirty needles, and hemophiliac clotting protein injections (all but the shared needles are really unlikely now). Casual, occupation hazards, and blood to open wound contact are also low and very unlikely. Really the only way you can become infected by HIV is through your own lifestyle.
The epicenter for HIV is in Central (sub-Saharan) Africa. The second epicenters are Haiti, the US, and France. 60% of all HIV infected persons (out of 12-10 million) live in Africa. HIV is environmentally fragile. That means it can?t survive heat, drying out, or disinfectants. GP-120, the surface maker for HIV only affects cells with CD4 markers. Dendritic cells are special CD4 cells that line the mucus, vigina, penis, and lower rectum. Life expectancy is 6-8 years (sometimes 10-12) from the time of infection. Once you get opportunistic infections, the life expectancy is 1-3 years. It takes two days to two weeks (sometimes 6 months) for the body to develop antibodies to try and stop HIV.
HIV reaches the interior of a cell and the genes start to cause the cell to replicate more viruses. In this way, the infection moves from cell to cell organism to organism. It attaches to its target cell in a standard way. The GP-120 surface antigen interacts with a glyprotein cell surface maker CD4. It penetrates the cell via membrane fusion and proceeds to unwrap its RNA genes. The RNA must be turned into DNA. Using reverse transcriptase, the viral RNA is made into DNA. Thus, the viral DNA gene-copies are in the cell?s genome permanently (or until it dies). The virus infection is now forever in the cell. When the cell undergoes division, the viral genes are also replicated. After the viral DNA has been made the new viruses are assembles and then released by budding.
HIV infects macrophages and T4 cells, so when the immune system starts working to kill off the infected cells, it is actually killing its own self. HIV is hard to fight because of its antigenetic drift. Antigenetic drift is a mutation, or change in the surface markers on the cell. Since the surface markers have changed, the antibodies made to combat it can?t recognize the virus. This can happen so rapidly that 15-17 HIV varieties can form during the duration of the infection. All strands remain active in the body.
There are three different stages of HIV. Acute is the time from when you are first infected until the antibodies are made. You have brief flu-like symptoms. Chronic (asymptomatic) is while you display the antibodies. You show signs of the disease, but you fell fine. The T4-cells start to die off and you are likely to contact other infections. Crisis is where the T4 cell counts drops below 200 per milliliter of blood. You are classified as having full-blown AIDS. This is when the opportunistic infections occur.