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.