The
human immunodeficiency virus (HIV) is a retrovirus which causes acquired immune deficiency syndrome (AIDS) by its effects on the human immune system. A very small minority of scientists continue to question the connection between HIV and AIDS and even the very existence of HIV (see AIDS reappraisal).
History
The first AIDS cases were described in 1981. HIV was first proposed as the cause of AIDS by Luc Montagnier of France and Robert Gallo of the United States in 1983-1984, leading to some controversy regarding the priority. At the time, the virus was called Human T-Lymphotropic Virus type III (HTLV-III) or Lymphadenopathy-Associated Virus (LAV). In 1986, the genome of the virus was cloned and sequenced. The name HIV has been in use since 1986.
As of the end of 2004, there were an estimated 39.4 million people around the world living with HIV or AIDS, 25.4 million of whom were in sub-Saharan Africa.
In some parts of the United States, it is illegal for a person with HIV to knowingly infect a person with the virus. This is also the case in most Western countries.
At 2/13/2005, news reported that a man in New York is found to be infected with one multi-drug resistant HIV called 3-DCR HIV (3-Drug-Class-Resistant HIV-1).
It is important to note that this is only one case, and it has been reported in a press release rather than a properly peer-reviewed journal. The press release has few details about the actual case. It is therefore too early to read too much into this reported case.
Signs and symptoms
Acute infection with HIV is a very aspecific syndrome, which is easily missed due to its likeness to infectious mononucleosis and other viral infections. Fever, fatigue and rash are the most common symptoms, and many develop lymphadenopathy (swollen lymph nodes). Pharyngitis, myalgia and several other symptoms also occur (Kahn & Walker, 1998).
This seroconversion syndrome is different from AIDS, the immune disease that most untreated HIV-infected patients develop eventually.
A very small minority of scientists continue to question the connection between HIV and AIDS and even the very existence of HIV (see AIDS reappraisal).
Shortly after infection, the body produces specific antibodies; most HIV tests work by detecting the presence of these antibodies.
HIV and the immune response
Graph showing HIV virus and CD4+ levels over the course of an untreated infectionInfection begins with an acute viremia. After this acute phase, the virus count drops up to 100 fold. From this alone, we see that the body seems to have a response to the HIV virus.
After the acute viremia, a period of clinical latency begins. At first this was believed to be true viral latency whereby the HIV was inserted in the host genome in an unproductive state awaiting certain body conditions to begin transcription. This implied the final fatal phase was just a breakdown of the asymptomatic phase causing transcription. There was subsequently a great deal of research into HIV transcription factors. Unfortunately, until about 1993, the sensitivity of viral assays was very poor meaning useful advances were not possible. The use of PCR amplification techniques from 1993 onwards meant that viral counts as low as 50 copies/ml were now detectable.
Around this time, attention also switched to the analysis of HIV in lymphoid tissue. Dendritic cells were found coated with virions, showing that the so called latent phase is not latent at all, virus levels are still high.
Treatment
The chemical structure of AZT. AZT, a reverse transcriptase inhibitor, was the first treatment for HIVPatients today are given a complex regimen of drugs that attack HIV at various stages in its life cycle. These are known as antiretroviral drugs. They include:
Protease inhibitors (PIs) inhibit activity of protease, an enzyme used directly by HIV to cleave nascent viral proteins, and so prevent final assembly of HIV virions.
Reverse transcriptase inhibitors (RTIs) inhibit the activity of reverse transcriptase, an enzyme HIV needs to complete infection of a cell. Lack of this enzyme prevents HIV from building pro-viral DNA based on its RNA. They come in three forms:
Nonnucleoside reverse transcriptase inhibitors (NNRTIs)
Nucleoside analog reverse transcriptase inhibitors (NARTIs or NRTIs)
Nucleotide analog reverse transcriptase inhibitors (NtARTIs or NtRTIs)
Entry inhibitors inhibit the viral entry into the cell interacting directly with the viral receptor and avoiding the fusion of the viral membrane with the target cell membrane.
Many problems are involved in establishing a course of treatment for HIV. Each effective drug comes with side effects, often serious and sometimes life-threatening in themselves. Common side effects include extreme nausea and diarrhea, liver damage and failure, and jaundice. Any treatment requires regular blood tests to determine continued efficacy (in terms of T-cell count and viral load) and liver function.
Also, no cases are known in which antiviral therapy has been able to terminate HIV infection. More than incremental improvements will be required to change this picture, meaning that HIV-infected people will likely have to stay on treatment life-long. Still, mortality is much lower among people with properly treated HIV infection than among HIV-positive people who got treated either at a late stage of infection or not at all. An important consequence of this is that people with access to adequate healthcare who have acquired HIV are today much better off if they know their status than if they learn about their infection only when symptoms of immune decline appear.
Immunity
About 10% of all Europeans carry a polymorphism of CCR5, a cell surface receptor involved in M-tropic HIV-1 infections. M-tropic HIV-1 uses CCR5 and CD4 receptors to enter target cells, unlike T-tropic HIV which uses CXCR4 with CD4. About 1% of all Europeans are homozygous for this mutation (a 32 base pair deletion), and have a very low risk of HIV-1 infection, although not complete protection.
There is evidence that other individuals may be immune or highly resistant to HIV infection. For instance, studies of prostitutes in sub-Saharan Africa have found some individuals who test negative for HIV despite years of unprotected exposure to hundreds of partners in populations with some of the highest infection rates in the world. This effect, if real, is not yet well understood.
Common misconceptions regarding HIV
HIV budding from an infected human immune cell"AIDS and HIV are the same thing".
While HIV is the virus that causes AIDS, AIDS refers to the set of immune deficiency symptoms that often do not surface for years after initial infection. Certain types of AIDS defining illnesses must be present for a person to be diagnosed as having AIDS, including a low CD4+ count, typically of 200 or less. HIV itself is a retrovirus that lives in the host before and durring the onset of AIDS.
"AIDS is not caused by HIV, but by poverty, anti-HIV drugs etc."
In AIDS, a number of diseases opportunistically occur. Most of them generally affect in persons with weakened immune systems, but in AIDS, HIV is defined as the ultimate cause. Today, AIDS is diagnosed via the helper T-cell count; in the 1980s unusually severe cases of a combination of opportunistic diseases were considered diagnostic. This obviously resulted in cases in which individuals with symptoms similar to AIDS, but not caused by HIV but by poverty, bad living conditions etc received anti-HIV treatment. (It should be remembered that much of what we 'knew' about HIV until the mid-1990s was misleading and/or even plain wrong). Since the early antiretroviral drugs were highly toxic (most notoriously AZT), this treatment was counterproductive. It should be noted that AIDS was only described in the 1980s, after the start of the HIV epidemic, while similar conditions - wasting, decreased resistance against infections - due to poverty etc. have been around for centuries without raising much interest. Thus, it was the increased occurrence of opportunistic diseases in individuals who would not be expected to suffer from them that alerted doctors that something was wrong. Additionally, what opportunistic diseases occur in AIDS can vary, tuberculosis being more prevalent in Eastern Europe/Russia, hepatitis among IV drug users etc.
"HIV only affects homosexuals and drug users".
Though the risk for infection is indeed statistically greater for gay men and injection drug users, HIV can infect anyone. Babies, women, senior citizens, teenagers, and people of any ethnicity can contract HIV.
"There is no risk to two people already infected to have unprotected sex".
HIV superinfection (or coinfection as it is sometimes called) has thought to be a consequence of unprotected sexual encounters between HIV infected people. Superinfection occurs when a person with HIV gets passed the same strain or a completely new strain, usually as a result of having unprotected sex with another HIV infected person. Superinfection has been demonstrated in laboratory studies as well as in animal trials. For years, proof that it could happen in real life situations has been hard to come by, but recent evidence has surfaced in human case studies that has confirmed that HIV superinfection can occur and can be very problematic for people with HIV.
"People over age 50 don't get HIV".
People over 50 can get HIV. The number of people over age 50 who are newly diagnosed with HIV infection is growing.
"An HIV positive woman can't give birth to a healthy baby".
HIV is sometimes transmitted from mother to unborn child, but not always. The risk is at least 20 to 30% for maternal-fetal transmission of HIV. Delivery via cesarean section and antiretroviral drugs taken during pregnancy can reduce the chance of mother to child infection; Where these treatments are available and the prospective mother is diagnosed early enough, only around two percent of HIV-positive mothers who carry the baby to term will give birth to an infected child. Post-partum infections via breastfeeding are also a problem, especially in the Third World where infant formula may not be available.
"A single identifiable person brought HIV to North America"
See Patient Zero.
Transmission of HIV
HIV can be passed through contact with contaminated bodily fluids. This includes blood and semen and any other bodily fluid that may be contaminated with blood. The most common form of transmission of HIV worldwide is sexual contact, whether vaginal or anal. Other significant sources of transmission of HIV has been through sharing of needles or through needlestick injuries (inadvertent injury with a contaminated sharp). HIV can also be spread through blood transfusions in cases where the donors were not screened or inadequately screened for HIV. Patients requiring frequent doses of blood products such as those with hemophilia are at increased risk here.
There is no evidence that HIV can be transmitted through hugging, shaking hands or other simple physical contact where there was no bleeding involved - including contact with carrier's sweat. HIV can theoretically be spread through kissing but the likelihood of this is very, very low unless there is some form of intraoral bleeding involved. There is no evidence that HIV can be spread through vectors such as mosquitoes.
Protection against transmission
Proper use of physical barriers such as the latex condom, have been shown to greatly reduce the risk of transmission of sexually transmitted diseases including HIV.
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