Human immunodeficiency virus (HIV) is a lentivirus (a member of the retrovirus family) that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive.
a. Acute infection
Infection with HIV generally occurs by introduction of bodily fluids from an infected person into the body of an uninfected person. This stage of infection lasts for a few weeks and is often accompanied by a short flu-like illness. During this stage there is a large amount of HIV in the peripheral blood and the immune system begins to respond to the virus by producing HIV antibodies and cytotoxic lymphocytes. This process is known as seroconversion. Some researchers use the term acute HIV infection to describe the period of time between when a person is first infected with HIV and when antibodies(proteins made by the immune system in response to infection) against the virus are produced by the body (usually 6 to 12 weeks) and can be detected by an HIV test.
Given the general character of these symptoms, they can easily have causes other than HIV, such as a flu infection. For example, if you had some risk for HIV infection a few days ago and are now experiencing flu-like symptoms, it is possible that HIV is responsible for the symptoms, but it is alsopossible that you have some other viral infection instead.
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b. Chronic stage
It may take years for HIV symptoms to develop. But even though no symptoms are present, the virus is multiplying (or making copies of itself) in the body during this time. HIV multiplies so quickly that the immune system cannot destroy the virus. After years of fighting HIV, the immune system starts to weaken.
The level of HIV in the peripheral blood drops to very low levels but people remain infectious and HIV antibodies are detectable in the blood, so antibody tests will show a positive result. During this phase of infection, HIV is active within lymph nodes, which typically become persistently swollen, in response to large amounts of virus that become trapped in the follicular dendritic cells (FDC) network.
During this stage of infection early initiation of antiretroviral therapy significantly improves survival, as compared with deferred therapy.
c. Progression from HIV to AIDS
As the immune system becomes more and more damaged the individual may develop increasingly severe opportunistic infections and cancers, leading eventually to an AIDS diagnosis.
AIDS occurs during the last stage of infection with HIV. If HIV goes untreated, AIDS develops in most people within 12 to 13 years after the initial infection. With treatment for HIV, the progression to AIDS may be delayed or prevented.
After your immune system starts to weaken, you are more likely to develop certain infections or illnesses, called opportunistic infections. The first symptoms often include moderate and unexplained weight loss, recurring respiratory tract infections (such as sinusitis, bronchitis, otitis media, pharyngitis), prostatitis, skin rashes, and oral ulcerations.
Receiving an AIDS diagnosis does not necessarily mean that the diagnosed person will die soon; some people have lived for many years after their diagnosis. This is even more the case today with the availability of highly active antiretroviral therapy (HAART), which has helped extend the lives of thousands of people living with HIV and AIDS.