HIV Human Immunodeficiency Virus

What is HIV?
HIV (human immunodeficiency virus) is the virus that causes AIDS (acquired immunodeficiency syndrome). By killing or damaging cells of your body's immune system, HIV progressively destroys your body's ability to fight infections and certain cancers. People diagnosed with AIDS may get life-threatening diseases called opportunistic infections, which are caused by microbes such as viruses, bacteria, or fungi. These infections do not usually make healthy people sick. Those with HIV/AIDS are also at an increased risk of developing certain cancers, neurological disorders, and a variety of other conditions.

In the United States, more than 980,000 diagnosed cases of AIDS were reported to the Centers for Disease Control and Prevention (CDC) between 1981 (when the first case was reported) and 2006. The CDC estimates that more than one million people in America may be infected with HIV and that as many as 250,000 of these may not know that they are infected and can pass on the virus to others.

Signs and Symptoms

HIV initially causes an acute illness with nonspecific or flu-like symptoms such as fatigue, headache, fever, and enlarged lymph nodes. Some people will not experience any noticeable symptoms. During this time period, the virus is present in large numbers and is carried throughout the body. HIV infects immune cells called CD4 T-cells (also called helper T cells) and slowly begins to decrease their numbers. The virus sets up house in places such as the brain and lymph nodes, where it will linger even during future drug treatment.

The patient’s immune system responds to the acute HIV infection by producing antibodies against the virus. In most people, the initial symptoms go away after a short time period. The patient may be apparently healthy for a decade or more but behind the scenes HIV is still replicating and destroying CD4 T-cells. Eventually, the affected person’s immune system is compromised to the extent that they begin having symptoms such as persistently enlarged lymph nodes, weight loss, sweating, recurrent yeast infections, fever, herpes infections, rashes, and memory loss or difficulty concentrating.

In children who are infected with HIV at or before birth, symptoms may emerge within a couple of years. They may have delayed development and be frequently ill.

When does AIDS develop?

The term AIDS applies to the most advanced stages of HIV infection. According to the CDC, AIDS is diagnosed when your CD4 T-cell count drops below 200 or when you have HIV and an AIDS-related illness such as tuberculosis or pneumonia caused by the microorganism Pneumocystis jirovecii (carinii). In people with AIDS, opportunistic infections are often severe and sometimes fatal because the immune system is so damaged by HIV that the body cannot fight off certain bacteria, viruses, fungi, and parasites.

Opportunistic infections common in people with AIDS cause symptoms such as:

coughing and shortness of breath
seizures and lack of coordination
difficult or painful swallowing
mental symptoms such as confusion and forgetfulness
severe and persistent diarrhea
vision loss
nausea, abdominal cramps, and vomiting
weight loss and extreme fatigue
severe headaches

How is HIV transmitted?

HIV is spread most commonly in these ways:

By having sex with an infected partner. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex.

Through contact with infected blood. Before blood was screened for evidence of HIV infection and before heat-treating techniques were introduced to destroy HIV in blood products, such as factor 8 and albumin, HIV was transmitted through transfusions of contaminated blood or blood components. Today, because of blood screening and heat treatment of blood derivatives, the risk of getting HIV from such transfusions is extremely small.

By sharing needles or syringes (such as with intravenous injection drug abuse), which can be contaminated with very small quantities of blood from someone infected with the virus. It is rare, however, for a patient to give HIV to a health care worker or vice-versa by accidental sticks with contaminated needles or other medical instruments.

During pregnancy or birth. Approximately one-quarter to one-third of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus. If the mother takes the drug AZT during pregnancy, she can significantly reduce the chances that her baby will be infected with HIV. If doctors treat mothers with AZT and deliver their babies by cesarean section, the chances of the baby being infected can be reduced to a rate of one percent.

Having a sexually transmitted disease such as syphilis, genital herpes, chlamydia, gonorrhea, or bacterial vaginosis, which appears to make people more susceptible to and at higher risk for acquiring HIV infection during sex with infected partners.

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On This Site
Tests: HIV antibody test, CD4 count, HIV genotypic resistance testing, HIV viral load, p24 antigen
Screening: Pregnancy, Newborns, Teens, Young Adults, Adults, Adults 50+
In the News: Rapid HIV Assays—Need for Confirmatory Tests Underscored by False Positives (2008), CDC Recommends Routine HIV Testing (2006), HIV Screening Recommendations Updated (2005), First Rapid HIV Test Using Oral Fluid Approved (2004), CDC: Make HIV Testing Routine (2003), HHS Extends Use of Rapid HIV Test to New Sites Nationwide (2003), FDA Approves New Rapid HIV Test Kit (2002)