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What Happens Inside the Body?  

Once HIV enters the human body, it attaches itself to a White Blood Cell (WBC) called CD4. Also, called T4 cells, they are the main disease fighters of the body. Whenever there is an infection, CD4 cells lead the infection-fighting army of the body to protect it from falling sick. Damage of these cells, hence can affect a person's disease-fighting capability and general health.
After making a foothold on the CD4 cell, the virus injects its RNA into the cell. The RNA then gets attached to the DNA of the host cell and thus becomes part of the cell's genetic material. It is a virtual takeover of the cell. Using the cell's division mechanism, the virus now replicates and churns out hundreds of thousands of its own copies. These cells then enter the blood stream, get attached to other CD4 cells and continue replicating. As a result, the number of the virus in the blood rises and that of the CD4 cells declines.

Because of this process, immediately after infection, the viral load of an infected individual will be very high and the number of CD4, low. But, after a while, the body's immune system responds vigorously by producing more and more CD4 cells to fight the virus. Much of the virus gets removed from the blood. To fight the fast-replicating virus, as many as a billion CD4 cells are produced every day, but the virus too increases on a similar scale. The battle between the virus and the CD4 cells continues even as the infected person remains symptom-free.

But after a few years, which can last up to a decade or even more, when the number of the virus in the body rises to very high levels, the body's immune mechanism finds it difficult to carry on with the battle. The balance shifts in favour of the virus and the person becomes more susceptible to various infections. These infections are called Opportunistic Infections because they swarm the body using the opportunity of its low immunity. At this stage, the number of CD4 cells per millilitre of blood (called CD4 Count), which ranges between 500 to 1,500 in a healthy individual, falls below 200. The Viral Load, the quantity of the virus in the blood, will be very high at this stage.

Opportunistic infections are caused by bacteria, virus, fungi and parasites. Some of the common opportunistic infections that affect HIV positive persons are: Mycobacterium avium complex (MAC), Tuberculosis (TB), Salmonellosis, Bacillary Angiomatosis (all caused by bacteria); Cytomegalovirus (CMV), Viral hepatitis, Herpes, Human papillomavirus (HPV), Progressive multifocal leukoencephalopathy (PML) (caused by virus); Candidiasis, Cryptococcal meningitis (caused by fungus) and Pneumocystis Carinii pneumonia (PCP). Toxoplasmosis. Cryptosporidiosis (caused by parasites). HIV positive persons are also prone to cancers like Kaposi's sarcoma and lymphoma.

The Center for Disease Control (CDC), Atlanta has listed a series of diseases as AIDS-defining. When these diseases appear, it is a sign that the infected individual has entered the later stage of HIV infection and has started developing AIDS. The progression of HIV positive persons into the AIDS stage is highly individual. Some people can reach the AIDS stage in about five years, while some remain disease free for more than a decade. Measurement of the viral load and the CD4 count helps a doctor in assessing an infected person's health condition.