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AIDS + HIV
Introduction
Being one of the most fatal viruses in the nation, AIDS (Acquired
Immunodeficiency Syndrome) is now a serious public health concern in most major
U.S. cities and in countries worldwide. Since 1986 there have been impressive
advances in understanding of the AIDS virus, its mechanisms, and its routes of
transmission. Even though researchers have put in countless hours, and millions of
dollars it has not led to a drug that can cure infection with the virus or to a vaccine
that can prevent it. With AIDS being the leading cause of death among adults,
individuals are now taking more precautions with sexual intercourse, and medical
facilities are screening blood more thoroughly. Even though HIV ( Human Immunodeficieny Virus) can be transmitted through sharing of non sterilize needles
and syringes, sexual intercourse, blood transfusion, and through most bodily fluids,
it is not transmitted through casual contact or by biting or blood sucking insects.
Development of the AIDS Epidemic
The first case of AIDS were reported in 1982, epidemiologists at the Center of
Disease Control immediately began tracking the disease back wards in time as well
as forward. They determined that the first cases of AIDS in the United States
probably occurred in 1977.
By early 1982, 15 states, the District of Columbia, and 2 foreign countries
had reports of AIDS cases, however the total remained low: 158 men and 1 woman.
Surprising enough more then 90 percent of the men were homosexual or bisexual.
Knowing this more then 70 percent of AIDS victims are homosexual or bisexual
men, and less then 5 percent are heterosexual adults. Amazing enough by
December of 1983 there were 3,000 cases of AIDS that had been reported in adults
from 42 states, the District of Columbia, and Puerto Rico, and the disease had been
recognized in 20 other countries.
Recognizing the Extent of Infection
The health of the general homosexual populations in the area with the
largest number of cases of the new disease was getting looked at a lot closer by
researchers. For many years physicians knew that homosexual men who reported
large numbers of sexual partners had more episodes of venereal diseases and were
at higher risk of hepatitis B virus infection than the rest of the population, but
conicidentally with the appearance of AIDS,. other debilitating problems began to do
appear more frequently. The most common was swollen glands, often accompanied
by extreme fatigue, weight loss, fever, chronic diarrhea, decreased levels of blood
platelets and fungal infections in the mouth. This condition was labeled ARC (AIDS
Related complex).
The isolation of HIV in 1983 and 1984 and the development of techniques to
produce large quantities of the virus [paved the way for a battery of tests to
determined the relationship between AIDS and ARC and the magnitude of the
carrier problem. Using several different laboratory tests, scientists looked for
antibodies against the HIV in the blood of AIDS and ARC patients. They found that
almost 100 percent of those with AIDS or ARC had the antibodies-they were
seriopostive. In contrast less then one percent of persons with no known risk factors
were seropositive.
Definition of AIDS
AIDS is defined as a disease, at least moderately predictive of defects in cell-
meditated immunity, occurring in a person with no known cause for diminished
resistance to that disease. Such diseases include Kaposi's Sarcoma, Pneumocystis
carnii pneumonia, and serious other opportunistic infections. After the discovery of
HIV and the development of HIV-antibody test, the case definition of AIDS was
updated to reflect the role of the virus in causing AIDS, but the scope of the
definition remained almost the same.
Transmission
HIV is primarily a sexually transmitted disease, it is transmitted by both
homosexual and bisexual and heterosexual activity. The first recognized case was
among homosexual and bisexual men. Many numbers of studies have shown that
men who have sexual partners and those who practice receptive anal intercourse
are more likely to be infected with HIV than other homosexual men. Researchers
found a strong connection between HIV infection and rectal trauma, enemas before
sex, and physical signs of disruption of the tissue lining the rectum.
Homosexual women tend to have a very low incidence of venereal disease in
general, an AIDS is no exception. Female-to-female transmission is highly
uncommon, however it has been reported in one case and suggested in another. In
the reported case, traumatic sex practices apparently resulted in transmission of HIV
from a woman who had acquired the virus through IV drug abuse to her non-drug-
using sexual partner.
1983 was when the first heterosexual (Male to female; female to male)
transmission was reported. In 1985, 1.7 percent of the adult cases of AIDS reported
to the CDC (Center for Disease Control) were acquired through heterosexual
activity; projections suggest that by 1991 the proportion will rise to 5 percent.
Heterosexual contact is the only transmission category in which women outnumber
men with AIDS. Heterosexual contacts accounts for 29 percent of AIDS cases
among women in the United States, but for only 2 percent of cases among men.
Estimates of the risk of HIV transmission in unprotected intercourse with a person
known to be infected with HIV are 1 in 500 for a single sexual encounter and 2 in 3
for 500 sexual encounters. The use of a condom reduces these odds to 1 in 5,000
for a single encounter and to 1 in 11 for 500 encounters.
Routes NOT Involved in Transmission of HIV
A study of more than 400 family members of adult and pediatric AIDS
patients demonstrate that the virus is not transmitted by any daily activity related to
living with or caring for an AIDS patient. Basically meaning that personal
interactions typical in family relationships, such as kissing on the cheek, kissing on
the lips, and hugging, have not resulted in transmission of the virus.
Patterns
There are three different geographic patterns of AIDS transmission. The first
one is characteristic of industrializing nations with large numbers of reported AIDS
cases, such as the United States, Canada, countries in Western Europe, Australia,
New Zealand, and parts of Latin America. In these areas most AIDS cases have been
attributed to homosexual or bisexual activity and intravenous drug abuse. The
second pattern is seen in areas of central, eastern, and southern Africa and in some
Caribbean countries. Unlike pattern one most AIDS cases in these areas occur
among heterosexuals, and the male-to-female ratio approaches 1 to 1. The third
pattern of transmission occurs in regions of Eastern Europe, the Middle East, Asia,
and most of the Pacific. It is believed that HIV was introduced to these areas in the
early to mid-1980s.
Any study associated with AIDS must begin with the understanding that AIDS
is only one outcome of infection with HIV-1. People infected with the virus may be
completely asymptomtic; they may have mildly debiliating symptoms; or they may
have life-threatening conditions caused by progressive destruction of the immune
system, the brain, or both.
One of the first signs of HIV-1 infection in some patients is an acute fluelike
disease. The condition lasts from a few days to several weeks and is associated with
fever, sweats, exhaustion, loss of appetite, nausea, headaches, soar throat, diarrhea,
swollen glands, and a rash on the torso.
Some of the symptoms of the acute illness may result from HIV-1 invasion of
the central nervous system. In some cases the clinical findings have correlated with
the presence of HIV-1 in the cerebrospinal fluid. Symptoms disappear along with
the rash and other sings of acute viral disease. When the blood test for HIV-1
antibodies become available, researchers demonstrated the lymphadenopathy was a
frequent consequence of infection with the virus. Scientist do not know what causes
the wasting syndrome, but some experts believe that it might result from the
abnormal regulation of proteins called monokines.
Between 5 and 10 percent of patients with AIDS and HIV-related conditions
have bouts of acute aseptic meningtis. About two-thirds of AIDS patients have a
degenerative brain disease called subacute encephalitis. HIV infection also have
been associated with degeneration of the spinal cord and abnormalities of the
peripheral nervous system. Symptoms include progressive loss of coordination and
weakness. Involvement of the peripheral nervous system may result in shooting
pains in the limbs or in numbness and partial paralysis.
HIV destroys the body's defense capabilities, opening itself to whatever
disease-producing agents are present in the environment. The diagnosis of
secondary infection in AIDS patients and others with HIV infection is complicated
because some of the standard diagnostic tests may not work. Often such tests detect
the immune response to a disease-producing microorganism rather than the
organism itself.
The most common life threatening opportunistic infection in AIDS patients is
Pneumocystis carinii Pneumonia, a parasitic infection previously seen almost
exclusively in cancer and transplant patients receiving immunosuppressive drugs.
The first signs of disorder are moderate to severe difficulty in breathing, dry cough,
and fever.
Infection
Infection with HIV is a 2-step process consisting of binding and fusion. The
larger protein, glycoprotein120, is responsible for the binding activity. Its target is a
receptor molecule called CD4, found on the surface of some human cells. The tight
complex formed by glycoprotein120, and CD4 receptor brings the viral envelope
very close to membrane of the target cell. This allows the smaller envelope protein,
glycoprotein41, to initiate a fusion reaction. The envelope of the virus actually fuses
with the cell membrane, allowing the viral core direct access to the inner
mechanisms of the human cell. Once the viral core is inside the cell, the viral RNA
genome is reverse transcribed into DNA and then integrated into the host genome
cells.
Cells infected with HIV carry envelope proteins lodged in their membrane.
These cell-bound proteins can bind to CD4 receptors on uninfected cell. Fusion of
the two cell membranes allow partially formed viral particles to move from the
infected cell to the uninfected cell. Thus, HIV theocratically could spread through
the body without leaving host cells.
Cell Death
HIV infects many different cell types, but it preferentially kills the T4
lymphocyte. There have been suggestions the T4 cells are more vulnerable to HIV-
induced cell death than other cells because they have a higher concerntration of
CD4 receptors. There is speculation that cell death occurs when viral envelope
proteins lodged in the membrane of an infected cell bind to CD4 receptors
embedded in the same membrane. Multiple self fusion reactions could destabilize
the cell membrane and kill the cell.
The massive depletion of T4 cells involves the cell-to-cell fusion reaction
described above. A single infected cell with a high concentration of viral envelope
proteins on its surface can bind to hundreds of uninfected T4 cells. The fused cells
form giant, mulitnucleated structures called syncytia, which are extremely unstable
and die within a day. One cell with a productive viral infection can cause the death
of up to 500 normal cells. Cell death might be related to the presence of free-
floating viral envelope proteins in the bloodstream. These could bind to uninfected
T4 cells, leading to their elimination by the immune system. Other autoimmune
mechanisms also may play a roll in T-cell depletion.
HIV infection also may directly or indirectly suppress the production of new
T4 cells. Direct suppression would occur if HIV damaged T precursor cells in the
bone marrow. Indirect suppression would result if HIV interfered with the
production of specific growth factors. On the other hand, infected cells may secrete
a toxin that shortens the lifespan of T4 cells or other cells required for their survival.
Immune System
The Immune response to HIV infection, does not appear to halt the
progression of disease. Part of the explanation for this failure probably relates to the
structure of the envelope proteins. The most effective way to stop HIV infection
would be to block the binding reaction between the glycoprotein120 and the CD4
receptor. However, antibodies from infected patients rarely do this. Scientists
speculate that 2 or 3 regions of the glycoprotein120 molecule involved in the
binding reaction may form a recessed pocket. The inability of antibodies to get
inside such a pocket could explain the lack of protective immune response.
The envelope proteins also are heavily coated with sugar residues. The
human immune system does not recognize the sugar residues as foreign because
they are products of the host cell rather then the virus. The sugar residues form a
protective barrier around sections of the glycoprotein120 that might otherwise elicit
a strong immune response.
Regulatory Genes
There has been recent studies that indicate HIV's unusual regulatory genes
contributing to its ability to evade the immune system. In the simplest retroviruses
the replication rate is controlled by interactions between the host cell and elements
in the viral LTR. The virus itself has no way of regulating when, here, or how much
virus is produced. In contrast, the human immunodeficiency viruses have elaborate
regulatory control mechanisms in the form of specific genes. Some of the genes
permit explosive replication; other appear to inhibit production of virus.
Mechanisms that suppress the production of certain viral proteins, such as the
envelope proteins, may allow HIV to hide inside infected cells for long periods
without eliciting antibodies or other host immune responses.
Conclusion
As stated above in the last few pages, AIDS is the leading cause of death in
homosexual, and bisexual adult men. However, these statistics were from 1986, 11
years later it has grown to more, not just in homosexual and bisexual men, but also
in heterosexual sexual intercourse. At this point in time there is no cure, nor is
there a vaccination. However, there are ways to prevent HIV, some of those ways
are: abstinence, condoms, not sharing needles used for IV drugs. Public concern is
higher then it was 10 years ago, but that's because people are starting to realize that
not everyone is immune to it, as of right now the only ones immune to the HIV virus
are baboons.BACK TO DIRECTORY | BACK TO SUB DIRECTORY: BIOLOGY
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