HIV (Human Immunodeficiency Virus) is the virus that causes AIDS (Aquired Immune Deficiency Syndrome).
ORIGIN OF THE VIRUS
The generally accepted hypothesis as to how the virus came into existance is that the Simian Immunodeficiency Virus (which infects chimpanzees) made the leap from chimps to humans early in the 20th century, after years of tribes of Africans consuming the flesh of chimps infected with the virus.
STAGES OF THE VIRUS
There are 4 main stages of infection: the incubation period, acute infection, latency stage, and full-blown AIDS.
During the incubation period (which begins at the moment of infection and generally lasts between 2 and 4 weeks), patients are usually (but not always) asymptomatic (meaning they present no symptoms).
ACUTE INFECTION PERIOD
Next comes the acute infection period (generally lasting 28 days), in which symptoms are very similar to those of the flu, such as swollen lymph nodes, sore throat, sore and weak muscles, and fever.
After the acute infection period comes the latency stage where patients will again experience few or no symptoms. This can last anywhere from 2 weeks to 20 years (or longer). It is the objective of physicians to keep the virus in this latency period for as long as possible in order to lengthen patients' lives.
And finally comes full-blown AIDS. This last stage is characterized by a CD4+ T cell (cells that help fight infection) count (measured in cells/microliter of blood) that is so low that any simple infection can be life threatening.
FACTS ABOUT HIV/AIDS
Patients can "toggle" back and forth between HIV and AIDS, as their T cell count rises above or drops below the critical cell count level. AIDS invariably results in death, however. Once a human contracts the HIV virus, they will never be completely rid of it. It is important to note that HIV does not kill directly, it simply compromises the body's immune system, making it possible for a simple virus or bacterium to invade the body (which cannot fight off the invader) and cause death.
CONTRACTION OF HIV
HIV is usually passed via the transmission of body fluids. This includes blood, semen, and vaginal secretions. Some viral particles can be found in the saliva, however it is highly unlikely that a human could be infected by swallowing saliva from an HIV positive individual. It is speculated that a human would have to ingest at least a pint of saliva before there would be any measureable risk of infection. Generally, individuals contract the virus through either an infected blood transfusion (which is far less common now that blood banks screen all blood before it's administered to a patient), from a syringe that had been used recently by an HIV positive user, or through unprotected sex with an HIV carrier. This includes oral, anal, and vaginal sex (HIV does not discriminate and almost anyone can be infected, regardless of age, race, sex, or sexual orientation).
GROUPS AT HIGHER RISK
However 2 groups of humans are at a higher risk of contracting the virus: gay men (because they engage in anal sex and the membrane lining the rectum is fairly thin and thus semen can pass through it and enter the blood stream relatively easily) and intravenous drug users (for obvious reasons).
HUMANS WITH IMMUNITY TO HIV
I say "almost everyone" because contrary to popular belief, some humans are immune to the virus. These humans lack the cellular receptors which the virus initially binds to in order to initiate infection (which occurs when the virus injects its RNA (ribonucleic acid, which is the genetic material in the HIV molecule) into a new host cell). Roughly 1 in 400 humans possess this immunity (but don't go out and try to find out if you are that 1 human!).
TREATMENT OF HIV POSITIVE PATIENTS
Treatment of HIV positive patients consists of drug coctails such as HAART (Highly Active Anti-Retroviral Treatment). The aim of this treatment is to lower the viral load in patients, causing the virus to become dormant and the patient to reenter the latency stage, thereby extending the patients' lives. Some patients find the side effects too unbearable, however most understand that the treatment is the best chance for a longer life (as opposed to no treatment) and decide to tolerate them.
TESTING FOR HIV
And finally, to determine whether a human is HIV positive or negative, an Enzyme-Linked Immunosorbent Assay (ELISA) test may be administered. If there is no reaction, the patient is considered HIV negative. However if there is a reaction, the test will be run again (to ensure the result was not a false positive), and if the result is again positive, another test will be run. The other test that may be administered is the Western Blot or, less commonly, the Immunofluorescence Assay (IFA). Only after both the ELISA and either the Western Blot or the IFA tests come back reactive several times is a patient considered HIV positive.
PREVENTING HIV BEFORE EXPOSURE
HIV can be prevented by knowing your partner's/partner(s)' HIV status(es), ALWAYS using condoms (FROM THE FIRST MOMENT OF SEXUAL CONTACT), and abstaining from the use of IV drug use.
PREVENTING HIV AFTER EXPOSURE TO THE VIRUS
As far as prevention after exposure to the virus is concerned, there is a drug that, if administered immediately after exposure, can prevent infection. It works by covering the aforementioned receptor sites, thus blocking the virus from infecting new host cells.