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HIV
From Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/HIV)
Human immunodeficiency virus (HIV) is a
retrovirus
that
immunodeficiency
causes
syndrome
acquired
(AIDS,
a
condition in humans in which the immune
system
begins
to
fail,
leading
to
life-
threatening opportunistic infections). Previous
names for the virus include human Tlymphotropic
virus-III
(HTLV-III),
lymphadenopathy-associated virus (LAV), or
AIDS-associated retrovirus (ARV).
Infection with HIV occurs by the transfer of
blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is
present as both free virus particles and virus within infected immune cells. The three major
routes of transmission are unprotected sexual intercourse, contaminated needles, and
transmission from an infected mother to her baby at birth, or through breast milk. Screening
of blood products for HIV in the developed world has largely eliminated transmission through
blood transfusions or infected blood products in these countries.
HIV infection in humans is now pandemic. As of January 2006, the Joint United Nations
Programme on HIV/AIDS (UNAIDS) and the World Health Organization (WHO) estimate that
AIDS has killed more than 25 million people since it was first recognized on December 1,
1981, making it one of the most destructive pandemics in recorded history. In 2005 alone,
AIDS claimed an estimated 2.4–3.3 million lives, of which more than 570,000 were children.
It is estimated that about 0.6% of the world's living population is infected with HIV. A third of
these deaths are occurring in sub-Saharan Africa, retarding economic growth and increasing
poverty. According to current estimates, HIV is set to infect 90 million people in Africa,
resulting in a minimum estimate of 18 million orphans. Antiretroviral treatment reduces both
the mortality and the morbidity of HIV infection, but routine access to antiretroviral
medication is not available in all countries.
HIV primarily infects vital cells in the human immune system such as helper T cells
(specifically CD4+ T cells), macrophages and dendritic cells. HIV infection leads to low levels
of CD4+ T cells through three main mechanisms: firstly, direct viral killing of infected cells;
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secondly, increased rates of apoptosis in infected cells; and thirdly, killing of infected CD4 + T
cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4+ T cell numbers
decline below a critical level, cell-mediated immunity is lost, and the body becomes
progressively more susceptible to opportunistic infections. If untreated, eventually most HIVinfected individuals develop AIDS (Acquired Immunodeficiency Syndrome) and die; however
about one in ten remains healthy for many years, with no noticeable symptoms. Treatment
with anti-retrovirals, where available, increases the life expectancy of people infected with
HIV. It is hoped that current and future treatments may allow HIV-infected individuals to
achieve a life expectancy approaching that of the general public (see Treatment).
Transmission
Since the beginning of the pandemic, three main transmission routes for HIV have been
identified:
Estimated per act risk for acquisition of HIV by exposure route [46]
Exposure Route
Estimated infections per
10,000 exposures to an
infected source
Blood Transfusion
9,000[47]
Childbirth
2,500[48]
Needle-sharing injection drug use
67[49]
Receptive anal intercourse*
50[50][51]
Percutaneous needle stick
30[52]
Receptive penile-vaginal intercourse*
10[50][51][53]
Insertive anal intercourse*
6.5[50][51]
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Insertive penile-vaginal intercourse*
5[50][51]
Receptive oral intercourse*
1[51]§
Insertive oral intercourse*
0.5[51]§
§

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*
assuming no condom use
Source refers to oral intercourse performed on a man
Sexual route. The majority of HIV infections are acquired through unprotected
sexual relations. Sexual transmission can occur when infected sexual secretions of
one partner come into contact with the genital, oral, or rectal mucous membranes of
another.

Blood or blood product route. This transmission route can account for infections in
intravenous drug users, hemophiliacs and recipients of blood transfusions (though
most transfusions are checked for HIV in the developed world) and blood products. It
is also of concern for persons receiving medical care in regions where there is
prevalent substandard hygiene in the use of injection equipment, such as the reuse
of needles in Third World countries. HIV can also be spread through the sharing of
leeches. Health care workers such as nurses, laboratory workers, and doctors, have
also been infected, although this occurs more rarely. People who give and receive
tattoos, piercings, and scarification procedures can also be at risk of infection.

Mother-to-child transmission (MTCT). The transmission of the virus from the
mother to the child can occur in utero during the last weeks of pregnancy and at
childbirth. In the absence of treatment, the transmission rate between the mother and
child is 25%. However, where drug treatment and Cesarian section are available, this
can be reduced to 1%. Breast feeding also presents a risk of infection for the baby.
HIV-2 is transmitted much less frequently by the MTCT and sexual route than HIV-1.
HIV has been found at low concentrations in the saliva, tears and urine of infected
individuals, but there are no recorded cases of infection by these secretions and the
potential risk of transmission is negligible. The use of physical barriers such as the latex
condom is widely advocated to reduce the sexual transmission of HIV. Spermicide, when
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used alone or with vaginal contraceptives like a diaphragm, actually increases the male to
female transmission rate due to inflammation of the vagina; it should not be considered a
barrier to infection. Research is clarifying the relationship between male circumcision and
HIV in differing social and cultural contexts, however critics point out that any correlation
between circumcision and HIV is likely to come from cultural factors (which govern not only
whether someone is circumcised, but also their sexual practices and beliefs). Even though
male circumcision may lead to a reduction of infection risk in heterosexual men by up to
60%, UNAIDS believes that it is premature to recommend male circumcision as part of HIV
prevention programs. Trials, in which some uncircumcised men were randomly assigned to
be circumcised in presumably sterile conditions and other men were not circumcised, have
been conducted in Kenya and Uganda. South African medical experts are concerned that
the repeated use of unsterilized blades in the ritual circumcision of adolescent boys may be
spreading HIV.
Tropism
The term viral tropism refers to which cell types HIV infects. HIV can infect a variety of
immune cells such as CD4+ T cells, macrophages, and microglial cells. HIV-1 entry to
macrophages and CD4+ T cells is mediated through interaction of the virion envelope
glycoproteins (gp120) with the CD4 molecule on the target cells and also with chemokine
coreceptors.
Macrophage (M-tropic) strains of HIV-1, or non-syncitia-inducing strains (NSI) use the βchemokine receptor CCR5 for entry and are thus able to replicate in macrophages and CD4+
T cells. This CCR5 coreceptor is used by almost all primary HIV-1 isolates regardless of viral
genetic subtype. Indeed, macrophages play a key role in several critical aspects of HIV
infection. They appear to be the first cells infected by HIV and perhaps the source of HIV
production when CD4+ cells become depleted in the patient. Macrophages and microglial
cells are the cells infected by HIV in the central nervous system. In tonsils and adenoids of
HIV-infected patients, macrophages fuse into multinucleated giant cells that produce huge
amounts of virus.
WHAT IS HIV
Taken from health24
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(http://www.health24.com/medical/Condition_centres/777-792-814-1753,33959.asp)
(http://www.health24.com/medical/Condition_centres/777-792-814-1753,33960.asp)

AIDS (Acquired Immunodeficiency Syndrome) is caused by HIV (the Human
Immunodeficiency Virus).

HIV is mainly transmitted through sexual intercourse.

Once a person is infected, the virus remains in the body for life.

One can be HIV positive and feel completely well for many years.

When a pregnant woman is infected, there is a one in three chance of her baby
becoming infected if no steps are taken to prevent this.

All people infected with HIV will eventually get AIDS.

AIDS is a fatal illness.

There is no drug that can cure HIV infection, but there are drugs that can control the
virus and delay the onset of AIDS.

There is no preventative HIV vaccine available at the moment, however research is
ongoing to find one
The Acquired Immune Deficiency Syndrome (AIDS) is caused by infection with the Human
Immunodeficiency Virus (HIV). HIV attacks and gradually destroys the immune system,
which protects the body against infections.
AIDS develops during the last stages of HIV infection. AIDS is not a single illness, but the
whole clinical picture (a syndrome) that occurs when the immune system fails entirely. A
person with a failing immune system is susceptible to a variety of infections that are very
unlikely to occur in people with healthy immune systems. These are called opportunistic
infections because they take advantage of the body's weakened immune system. Certain
types of cancers also occur when the immune system fails.
It may take years for a person's immune system to deteriorate to such an extent that the
person becomes ill and a diagnosis of AIDS is made. During this time (which can last from
less than one year to as long as 10 years or possibly even longer), a person may look and
feel perfectly well. This explains why so many people are unaware that they are infected with
HIV. However, even though they feel healthy, they can still transmit the virus to others.
More than 90% of people living with HIV are in developing countries, with sub-Saharan
Africa accounting for two thirds of all the HIV-infected people in the world. Unlike Western
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countries, where HIV has initially affected predominantly homosexual men, in Africa and
developing countries HIV is usually spread by sex between men and women (heterosexual
sex).
Research into HIV/AIDS is ongoing and new information is emerging rapidly. There are
drugs that can dramatically slow down the disease in an infected person. These drugs need
to be taken in various combinations in order to be effective and so treatment is generally
quite expensive. Also, individuals on the drugs must be monitored by medical personnel
trained in the use of antiretroviral therapy because these drugs can potentially cause serious
side effects if not taken correctly and if the individual is not monitored properly. However,
there is no cure for AIDS. There is also currently no preventative vaccine against HIV
infection. At this time the only effective strategy for controlling the spread of HIV is
prevention through individual behaviour change, spreading the correct information about
preventing HIV infection and the use of condoms and other safe sex measures. Other
measures, which should be taken by a country's health system, are screening of blood
products and the prevention of infection of patients through contaminated medical
equipment. Mother to child infection can be reduced by a short course of an anti-HIV drug
given to the mother and new-born baby at the time of delivery.
According to researchers, two viruses cause AIDS, namely HIV-1 and HIV-2. HIV-1 is the
predominant virus in most parts of the world, whereas HIV-2 is most commonly found in
West Africa. These viruses belong to a family called the retroviruses. They are unique
viruses in that they are able to insert their genetic material into the genetic material (DNA) of
cells of the person that they have infected. In this way they are able to persistently infect a
person for the rest of that person's life.
To understand how the virus eventually causes AIDS, see the section “Course of the
disease”.
For
detailed
discussion
of
evidence
that
HIV
causes
AIDS,
go
to
http://www.niaid.nih.gov/factsheets/evidhiv.htm
Viruses that are very closely related to HIV are found in other primates (apes and monkeys).
These viruses are called Simian Immunodeficiency Viruses (SIV). HIV-2 is genetically almost
indistinguishable from the SIV found in sooty mangabeys. A very close genetic relative of
HIV-1 has been found in chimpanzees. Therefore most scientists accept that the human
immunodeficiency viruses are recently derived from these primate viruses. The earliest
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blood sample found to contain HIV dates from 1959; this sample was collected in central
Africa.
Based on molecular technology and the use of large computer programmes, scientists have
been able to trace back the genetic origins of HIV-1 and HIV-2 and roughly pinpoint the time
when these viruses first appeared in humans. The current theory is that sometime between
1930-1940 there was a “species-jump” of certain SIV’s into human populations, probably
through the practise of slaughtering, preparing and consuming of “bush meat” from monkeys
in parts of Central and West Africa.
HIV is not as contagious as is often believed. The virus does not survive long outside the
body and can only be transmitted through the direct exchange of certain body fluids such as
blood, semen and vaginal fluid. The virus can gain access to the body at its moist surfaces
("mucous membranes") during sex, or through direct injection into the blood stream. Sex is
the major mode of transmission of HIV worldwide.
HIV can be transferred from one person to another (transmitted) through:

Unprotected vaginal or anal intercourse with an infected person

A mother’s infection passing to her child during pregnancy, birth or breastfeeding
(called vertical transmission) – the risk of HIV passing from mother to child is
approximately 30%

Injection with contaminated needles, which may occur when intravenous drug users
share needles, or when health care workers are involved in needleprick accidents

Use of contaminated surgical instruments, for example during traditional circumcision

Blood transfusion with infected blood

Contact of a mucous-membrane surface with infected blood or body fluid, for
example with a splash in the eye (Note that the virus cannot penetrate undamaged
skin.)
If a person is exposed to HIV in one of the above ways, infection is not inevitable. The
likelihood of transmission of HIV is determined by factors such as the concentration of HIV
present in the body fluids. For example, although HIV has been detected in saliva, the
concentration is thought to be too low for HIV to be transmitted through deep/wet kissing
since it would require the exchange of almost one litre of saliva between individuals before
there would be sufficient virus available for possible transmission. Additionally, a digestive
protein in human saliva tends to inactivate the virus.
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The risk of HIV transmission also depends on the stage of infection the HIV-positive sexual
partner is in. Virus concentrations in blood and body fluids are highest when a person has
very recently been infected with HIV, or otherwise very late in the disease, when AIDS has
developed. Very early after infection the virus can multiply rapidly as the immune system has
not had time to respond and fight back, and late in the disease the virus can multiply rapidly
because it has destroyed the immune system altogether. However, it is important to note
that once a person is infected with HIV, their blood, semen or vaginal fluids are always
infectious, for the rest of their lives.
Vulnerability to HIV infection through sexual contact is increased if a person has sores on
the genitals, mouth or around the anus/rectum. These sores can be caused by rough
intercourse, other sexually transmitted diseases (STDs), gum disease or overuse of
spermicides.
In heterosexual sex, women are more vulnerable to HIV infection because of the large
mucous-membrane surface area of the vagina compared to that of the urethra (penile
opening). Therefore, in regions where heterosexual sex is the main way HIV is transmitted
(as in South Africa), approximately four women are infected for every three men that are
infected.
Men who are circumcised have a significantly lower risk of being infected with HIV.
Fortunately, people can take action to reduce their risk of infection. For example, a person
who uses a condom every time he or she has sex is at far lower risk of infection than
someone who has unprotected sex.
The following outlines common sexual behaviours according to relative risk:
Very low risk

Masturbation (including mutual masturbation)

Oral sex on a man with a condom

Oral sex on a woman with a barrier method (such as plastic wrap, dental dam or a
condom cut open)
Low risk

Wet/deep kissing (when sores or gum disease, and therefore blood, are present)

Oral sex
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
Vaginal sex with a male or female condom

Anal sex with a male or female condom
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High risk

Anal intercourse without a condom

Vaginal sex without a condom
The receptive partner (vaginal or anal intercourse) is at much greater risk of being infected
from an HIV-positive partner than vice versa.
How HIV is not transmitted
Unfortunately, there are still many myths around HIV. A person cannot be infected through:

Mosquito bites

Urine or sweat

Public toilets, saunas, showers or swimming pools

Sharing towels, linen or clothing

Going to school with, socialising or working with HIV-positive people

Sharing cutlery or crockery

Sneezes or coughs

Touching or hugging

Kissing a person with HIV (when no blood is exchanged through cuts or sores

(Sexual) contact with animals, since HIV is strictly a human virus and is not carried
by animals
In South Africa, blood donated for transfusions or blood products is screened for antibodies
to HIV and for the presence of one of the viral proteins. In 2005, blood transfusion services
in South Africa introduced a test for HIV RNA (the genetic material of the virus) further
improving the safety of donated blood. Any contaminated blood is discarded. The probability
of HIV infection via blood transfusion in this country is therefore extremely low, but can
theoretically still occur because the tests used do not detect very early HIV infection (the first
few days) in a donor.