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.