HIV
Human immunodeficiency virus (commonly known as HIV, and formerly known as HTLV-III and lymphadenopathy-associated virus) is a retrovirus that primarily infects vital components of the human immune system such as CD4+ T cells, macrophages and dendritic cells. It also directly and indirectly destroys CD4+ T cells. As CD4+ T cells are required for the proper functioning of the immune system, when enough CD4+ T cells have been destroyed by HIV, the immune system functions poorly, leading to the syndrome known as AIDS. HIV also directly attacks organs, such as the kidneys, the heart and the brain leading to acute renal failure, cardiomyopathy, dementia and encephalopathy. Many of the problems faced by people infected with HIV result from failure of the immune system to protect from opportunistic infections and cancers.
HIV is transmitted through direct contact of a mucous membrane with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal fluid or breast milk. This transmission can come in the form of: penetrative (anal or vaginal) sex; oral sex; blood transfusion; contaminated needles; exchange between mother and infant during pregnancy, childbirth, or breastfeeding; or other exposure to one of the above bodily fluids.
AIDS is thought to have originated in sub-Saharan Africa during the twentieth century and is now a pandemic. At the end of 2004, UNAIDS estimated that nearly 40 million people were currently living with HIV. The World Health Organization estimated that the AIDS epidemic had claimed more than 3 million people and that 5 million people had acquired HIV in the same year. Currently it is estimated that 28 million people have died and that HIV is set to infect 90 million people in Africa, resulting in a minimum estimate of 18 million orphans in Africa alone.[2]
Introduction
In 1983, scientists led by Luc Montagnier at the Pasteur Institute in France first discovered the virus that causes AIDS. They called it lymphadenopathy-associated virus (LAV). A year later a team led by Robert Gallo of the United States confirmed the discovery of the virus, but they renamed it human T lymphotropic virus type III (HTLV-III). The dual discovery led to considerable scientific fall-out, and it was not until President Mitterand of France and President Reagan of the USA met that the major issues were ironed out. In 1986, both the French and the US names were dropped in favour of the new term human immunodeficiency virus (HIV).
HIV is a member of the genus lentivirus, part of the family of retroviridae. Lentiviruses have many common morphologies and biological properties. Many species are infected by lentiviruses, which are characteristically responsible for long duration illnesses associated with a long period of incubation. Lentiviruses are transmitted as single-stranded, positive-sense, enveloped RNA viruses. Upon infection of the target-cell, the viral RNA genome is converted to double-stranded DNA by a virally encoded reverse transcriptase which is present in the virus particle. This viral DNA is then integrated into the cellular DNA for replication using cellular machinery. Once the virus enters the cell, two pathways are possible: either the virus becomes latent and the infected cell continues to function or the virus becomes active, replicates and a large number of virus particles are liberated which can infect other cells.
Two species of HIV infect humans: HIV-1 and HIV-2. HIV-1 is the more virulent and easily transmitted, and is the source of the majority of HIV infections throughout the world; HIV-2 is largely confined to west Africa. Both species originated in west and central Africa, jumping from primates to humans. HIV-1 has evolved from a simian immunodeficiency virus (SIVcpz) found in the chimpanzee subspecies, Pan troglodytes troglodytes. HIV-2 crossed species from a different strain of SIV, found in sooty mangabey monkeys in Guinea-Bissau. It is possible that HIV-1 entered the human populations in the 1930’s.
Another controversial possibility for the origin of HIV/AIDS was discussed in a 1992 Rolling Stone magazine article by freelance journalist Tom Curtis. He put forward the theory that AIDS was inadvertently caused in the late 1950’s in the Belgian Congo by Hilary Koprowski’s research into a polio vaccine. Although subsequently retracted due to libel issues surrounding its claims, the Rolling Stone article encouraged another freelance journalist, Edward Hooper, to travel to Africa for 7 years of research into this subject. Hooper’s research resulted in his publishing a 1999 book, The River, in which he alleged that an experimental oral polio vaccine prepared using chimpanzee kidney tissue was the route through which SIV mutated into HIV and started the human AIDS epidemic, some time between 1957 and 1959.
Treatment:
HIV infection is a chronic infectious disease that can be treated, but not yet cured. There are effective means of preventing complications and delaying progression to AIDS. At the present time, not all persons infected with HIV have progressed to AIDS, but it is generally believed that the majority will. People with HIV infection need to receive education about the disease and treatment so that they can be active partners in decision making with their health care provider.
A combination of several antiretroviral agents, termed Highly Active Anti-Retroviral Therapy HAART, has been highly effective in reducing the number of HIV particles in the blood stream (as measured by a blood test called the viral load). This can improve T-cell counts. This is not a cure for HIV, and people on HAART with suppressed levels of HIV can still transmit the virus to others through sex or sharing of needles. There is good evidence that if the levels of HIV remain suppressed and the CD4 count remains greater than 200, then the quality and length of life can be significantly improved and prolonged. Improved antiretroviral inhibitors against proteins such as Reverse transcriptase, Integrase and Tat are being researched and developed. One of the most promising new therapies is a new class of drugs called fusion or entry inhibitors.
Current recommendations for treatment include at least a three drug effective regime to induce complete cease of viral replication and reduce the incidence of new mutations. Current drug classes include NNRTI, NRTI, NtRTI, PI, FI. Each of the drugs in these classes represent individual pharmacodynamics and toxicities, requiring expert knowledge to appropriately select and dose an effective combination.
Post-exposure prophylaxis (PEP) with a course of antiviral drugs is also thought to reduce the risk of seroconversion after high risk exposure (unprotected anal or vaginal sex) to HIV.[34] To be effective, it must be started as soon as possible after exposure and no later than 72 hours post-exposure. The treatment for HIV lasts four weeks. While there is compelling data to suggest that PEP after HIV exposure is extremely effective, there have been cases where it has failed.
As yet, no vaccine has been developed to prevent HIV infection or disease in people who are not yet infected with HIV, but the potential worldwide public health benefits of such a preventive vaccine are vast. Researchers in many countries are seeking to produce such a vaccine, including through the International AIDS Vaccine Initiative.
Comments are closed.