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Prevention & Treatment For AIDS
Sunday, February 1, 2009/ 1:08 AM
Prevention and Treatment of AIDS
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The most successful method for the prevention of most viral disease has been the development of vaccines. However, the development of a vaccine against HIV has been a very slow, frustrating, and to date unsuccessful process. This is perhaps not surprising in light of the fact that the virus establishes a persistent lifelong infection in the face of a vigorous immune response on the part of the host that succeeds in controlling the virus for many years. Vaccine development continues to be a priority, but to the current time only public education to slow the spread of the disease and the development of antiviral drugs have had any success in control of the virus.
Much effort has been made to reduce the epidemic spread of HIV by educating the public and thereby altering patterns of behaviour, especially sexual behaviour. AIDS is a significant health problem in the United States, particularly in urban areas, and has become one of the major causes of death for persons in their most productive years. However, safe sex practices, such as the use of condoms, have lowered the numbers of now infections, especially for HIV infections among gay white men. Education campaigns in Thailand and Uganda have succeeded in slowing the spread of the disease, and similar campaigns in other areas of the world have met with at least some success. However, although such campaigns slow the spread of the virus, they do not stop it and will never succeed in eliminating the virus from the population.
Although this therapy has been successful in many patients, it is clearly not a panacea. First, it is very expensive and suitable for use only in developed countries that can afford a very high level of health care. Second, it requires taking dozens of pills a day at precisely timed intervals, and compliance becomes a major issue when the therapy must be continued indefinitely. It may be for this reason that the therapy fails in a significant fraction of HIV patients. However, although this treatment is quite complex and of limited success, its very existence seemingly has led to a rise in unprotected sexual activity and to an upsurge in the rate of HIV infection among populations at risk.
Attempts to develop a vaccine continue and there is hope that a vaccine may ultimately be produced. It is clear that an immune response that involves both neutralizing antibodies and CD8+ T cells is important in the control of the virus during the clinically latent state. The T-cell response seems to be especially important. Stronger CTL responses result in lower levels of virus production during the latent state, which results in a slower rate of progression to AIDS. Neutralizing antibodies are also important, but it has been found that fresh isolates of virus from patients are difficult to neutralize, presumably because of the many carbohydrate chains attached to the HIV surface glycoprotein and because of the unusual folding properties of this protein. In addition, variants arise during prolonged infection that are resistant to the mix of antibodies that exist in the patient at the time that the variants arise.
The possibility of a live virus vaccine is suggested by the finding that a small fraction of infected people exists who have not progressed to AIDS after 10-15 years of infection and whose CD4+ T-cell count has remained fairly stable. In at least some of these individuals, the infecting HIV strain has deletions in nef. Intriguingly, experiments with nef deletions in SIV in monkeys give comparable results – the monkeys do not develop AIDS and they are protected from infection by wild-type strains of SIV. However, any attempt to develop a live virus vaccine for a virus that establishes a persistent infection that is ultimately fatal, and for which the symptom of disease are delayed for many years, faces formidable obstacles.
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