What is HIV?
The Human Immunodeficiency Virus (HIV) is the virus that leads to AIDS. HIV belongs to a subset of retroviruses called lentiviruses (or slow viruses), which means that there is an interval -- sometimes years -- between the initial infection and the onset of symptoms. Upon entering the bloodstream -- through mucous membranes or blood-to-blood contact -- HIV infects the CD4+T cells and begins to replicate rapidly.
Scientists believe that when the virus enters the body, HIV begins to disable the body's immune system by using the body's aggressive immune responses to the virus to infect, replicate and kill immune system cells. Gradual deterioration of immune function and eventual destruction of lymphoid and immunologic organs is central to triggering the immunosuppression that leads to AIDS.

What is AIDS?
Acquired Immunodeficiency Syndrome (AIDS) is the final stage of HIV infection. The Centers for Disease Control establish the definition of AIDS, which occurs in HIV-infected persons with fewer than 200 CD4+T cells and/or persons with HIV who develop certain opportunistic infections. In 1992, the CDC redefined AIDS to include 26 CDC-defined AIDS indicator illnesses and clinical conditions that affect persons with advanced HIV.

What are CD4+T or T cells?
CD4+T cells are the immune system's key infection fighters and the entity that allows HIV to enter, attach and infect the body's immune system. The CD4+T cells (also called T4 cells) are disabled and destroyed by the virus, often with no symptoms, causing a significant decrease in the blood levels of T4 cells. In the advanced stages of HIV, the body may have fewer than 200 T4 cells, while a healthy adult's count is 1,000 or more. In this way, the body's immune system is continuously weakened from the moment of infection and the inability of the immune system to fight infection opens the door to opportunistic infections.

What is the distinction between HIV and AIDS?
AIDS is a disease developed by a person living with HIV, which is a viral organism. The term AIDS applies to the most advanced stages of HIV infection. Although an HIV-positive test result does not mean that a person has AIDS, most people will develop AIDS as a result of their HIV infection.

There are four main stages in the progression of an HIV infected person developing AIDS. The period following the initial HIV infection is called the window period. It is called this because this period reflects the window of time between infection with the virus and when HIV antibodies develop in the bloodstream. An HIV test that looks for antibodies taken during this time can result in a false negative, though antibodies usually appear within six months of the initial infection.

Seroconversion refers to the period of time during which your body is busy producing HIV antibodies, trying to protect itself against the virus. This is the period after the initial infection when many people experience flu-like symptoms and swollen lymph nodes – this is a highly infectious stage.

After most people seroconvert, they usually experience a symptom-free period or asymptomatic period. This stage can last anywhere from 6 months to over 10 years, varying from person to person. Although the person with HIV is experiencing no symptoms, the virus is still replicating inside the body and weakening the immune system.

After this period, severe CD4+T cell loss leads to the symptomatic period, in which the body experiences the symptoms associated with HIV. This is the final stage before developing AIDS.

 What are the symptoms of HIV?
The only way to determine HIV infection is to be tested, as symptoms and latent periods vary from person to person. It is common during the first two to four weeks of infection that people experience flu-like symptoms and enlarged lymph nodes. This is because the virus migrates to various organs in the body, particularly the lymphoid organs. During this stage people are highly infectious and HIV is present in large quantities in genital secretions.

According to the Centers for Disease Control and Prevention, the following are symptoms that may be warning signs of HIV infections:

Rapid weight loss
Dry cough
Recurring fever or profuse night sweats
Profound and unexplained fatigue
Swollen lymph glands in the armpits, groin or neck
Diarrhea that lasts for more than a week
White spots or unusual blemishes on the tongue, in the mouth or in the throat
Pneumonia
Red, brown, pink or purplish blotches on or under the skin or inside the mouth, nose or eyelids
Memory loss, depression and other neurological disorders
Remember that the only way to determine HIV infection is to be tested for the virus. No one should assume they are HIV positive or negative based on the presence or absence of any of the above symptoms. Each symptom can be related to other illnesses; similarly, other symptoms or the absence of symptoms cannot assure that someone is HIV negative. To be certain, get tested.

How is HIV transmitted?
HIV infection most commonly occurs through sexual contact. However, the virus can also be spread through blood-to-blood contact -- such as sharing needles or blood transfusions involving unscreened blood. Studies have shown that HIV is not transmitted through casual contact such as touching or sharing towels, bedding, utensils, telephones, swimming pools, or toilet seats. Scientists have also found no evidence of transmission through kissing, sweat, tears, urine or feces. It is important to acknowledge that it is not sex that transmits HIV, but certain bodily fluids: blood, semen (including "pre-cum"), vaginal secretions and breast milk. High-risk behaviors that can result in HIV transmission are sharing needles for drugs, tattoos, body piercing, vitamins or steroids with an HIV-infected person and/or engaging in unprotected anal, vaginal or oral sex with a person who is HIV infected. The virus also can be transmitted from an HIV-infected mother to her child through pregnancy, birth or breastfeeding.

It does appear that persons already infected with a sexually transmitted disease are more susceptible to acquiring HIV during sex with an infected partner. Mucous membranes, a weak point in the skin, include the lips, mouth, vagina, vulva, penis or rectum. Because mucous membranes are porous and viruses and other pathogens are able to pass through, these areas are rich in immune cells. When a person already has a sexually transmitted disease, sex organs may be flooded with CD4+T cells, making it much easier for HIV to infect.

The only way to determine HIV infection is to be tested for the virus. It is not unusual for HIV-infected persons to experience symptoms years after the initial infection; some may be symptom free for over 10 years. However, during the asymptomatic period, the virus is actively multiplying and destroying cells in the immune system, weakening the body's ability to fight infection. The effect is most keenly observed in the decline of the immune system's key infection fighters in the blood, the CD4+T cells.