Difference between revisions of "Human Immunodeficiency Virus"
|Line 108:||Line 108:|
Revision as of 20:40, 12 November 2012
|Human Immunodeficiency Virus|
|Group VI (ssRNA-RT)|
|Species HIV1, HIV2|
| Part of a series on the AIDS Pandemic
The Human Immunodeficiency Virus (HIV) is the virus that causes AIDS. It is a lentivirus, (a type of Retrovirus). There are 2 known versions of Human Immunodeficiency Virus, both originally from monkeys, and both extremely virulent. The virus causes AIDS by infecting vital cells in the immune system, specifically the T helper cells, macrophages, and dendritic cells, without which, the immune system is rendered non-functioning. The virus itself is believed to be originally Simian Immunodeficiency Virus, that has evolved to target humans effectively. The virus is originally from Africa, as bushmeat hunters were infected, and through transfer of bodily fluid to other people, eventually found itself in North America, and subsequently, the rest of the world. HIV does not have an effective vaccine.
A French team of researchers has been given primary credit for the discovery, although the American scientist Gallo apparently discovered it independently.
In 1983, Barre-Sinoussi, Chermann, and Montagnier (at the Pasteur Institute in Paris) isolated a retrovirus from lymph node cells of a patient with lymphadenopathy; accordingly, this virus was designated lymphadenopathy-associated virus (LAV). Lymphadenopathy-associated virus was shown to replicate and cause cytopathology in cultures of human peripheral blood lymphocytes. A year after the report on LAV, Gallo and co-workers (at the National Institutes of Health, Bethesda, MD) described the isolation of a cytopathic T-lymphotropic retrovirus, designated human T-lymphotropic virus type III (HTLV-III), from peripheral blood lymphocytes of patients with acquired immunodeficiency syndrome (AIDS) Although this HTLV-III isolate was later shown to be a contaminant of virus from the Pasteur Institute, subsequent isolates of HTLV-III were unique. Also, in 1984, Levy and co-workers (at the University of California, San Francisco) cultured an AIDS-associated retrovirus (ARV) from peripheral blood mononuclear cells of an AIDS patient. Molecular cloning and sequence analysis revealed that the genomes of LAV and HTLV-III were nearly identical, exhibiting 1% to 2% divergence. In contrast, the genome of the ARV-2 isolate displayed up to 15% differences in nucleotide sequences in pairwise alignments with the genomes of either LAV or HTLV-III. Electron microscopy demonstrated that these viruses from AIDS patients were morphologically similar to members of the lentivirus genus of the family Retroviridae. Furthermore, comparison of genome sequences also supported the notion that the human retroviruses associated with AIDS were related, albeit distantly, to lentiviruses of other animals.
HIV is primarily spread by sexual contact and intravenous drug use. Most early infections in the US were via homosexual sex, and to a lesser extent via intravenous drug use and blood transfusions; most current infections in the world are via heterosexual contact and vertical transmission from mother to child. Mothers infected with HIV transmit the virus to their baby in utero, during childbirth. Mother-to-child transmission can be significantly reduced by the proper use of antiretroviral agents.
Until recently, it was thought that breastfeeding increased the risk of HIV transmission from mother to child. However, research in KwaZulu Natal  showed that babies of mothers with HIV who receive a mixture of milk and solid foods are 11 times more likely to become infected than those who are exclusively breastfed. Those given formula milk as well as breast milk are nearly twice as likely to become HIV positive. Even in countries with high HIV prevalence, it is calculated that exclusive breastfeeding could prevent 13% of deaths in children under five years-old.
The KwaZulu Natal study involved around 2,700 babies born between 2001 and 2005. Major efforts were made to encourage and support women in breastfeeding by sending counsellors to their homes twice a week. The success of the strategy surprised the researchers. The authors say exclusive breastfeeding "ordinarily protects the integrity of the intestinal mucosa, which thereby presents a more effective barrier to HIV".
Less commonly, contact with infected blood causes HIV transmission. This can occur in health care providers (HCPs) or others exposed to infectious bodily fluids. Transmission is facilitated by breaks in the skin or direct contact with mucosal tissues, such as those found in the eyes, mouth, anus, or vagina. Early in the epidemic, blood transfusions were a significant source of HIV transmission.
Other less likely means of transmission exist, though are rare. There are no confirmed cases from contact with the saliva, sweat or tears of an infected person.
Early on in the epidemic, there was much confusion about the transmission of HIV. After decades of study, this has been clarified. HIV can be found in various body fluids, however its highest concentrations are found in semen, blood, and vaginal secretions. It can also be found in breast milk, but recent research  shows that exclusive breastfeeding tends to protect against HIV transmission.
An exposure that might place HCP at risk for HIV infection is defined as a percutaneous injury (e.g., a needlestick or cut with a sharp object) or contact of mucous membrane or nonintact skin (e.g., exposed skin that is chapped, abraded, or afflicted with dermatitis) with blood, tissue, or other body fluids that are potentially infectious. In addition to blood and visibly bloody body fluids, semen and vaginal secretions also are considered potentially infectious. Although semen and vaginal secretions have been implicated in the sexual transmission of HIV, they have not been implicated in occupational transmission from patients to HCP.
Potentially Infectious Fluids
The risk for transmission of HIV infection from these fluids is unknown; the potential risk to HCP from occupational exposures has not been assessed by epidemiologic studies in health-care settings.
- cerebrospinal fluid
- synovial fluid
- pleural fluid
- peritoneal fluid
- pericardial fluid
- amniotic fluid.
The following fluids are not considered potentially infectious unless they are visibly bloody; the risk for transmission of HIV infection from these fluids and materials is low.
- nasal secretions
Any direct contact (i.e., contact without barrier protection) to concentrated virus in a research laboratory or production facility requires clinical evaluation. For human bites, clinical evaluation must include the possibility that both the person bitten and the person who inflicted the bite were exposed to bloodborne pathogens. Transmission of HIV infection by this route has been reported rarely.
Per-contact risk of HIV transmission:
- URA with a known seropositive partner: 0.82 percent
- URA with a partner of unknown serostatus, 0.27 percent (95% CI: 0.06, 0.49 percent)
- Unprotected insertive anal intercourse: 0.06 percent.
- Receptive oral sex: 0.04 percent.
(URA=unprotected receptive anal intercourse) AIDSWEEKLY Plus; Monday, August 9, 1999
"The overall, unadjusted probability of HIV-1 transmission per coital act is 0·0011 in this Ugandan population, and greater infectivity of predominant HIV-1 viral subtypes is unlikely to account for the explosive HIV-1 epidemic in sub-Saharan Africa. Transmission probability per act varies greatly with the HIV-1 viral load of the HIV-1-infected partner, which suggests that interventions to reduce viral load could reduce transmission.15,28 Younger age and genital ulceration also increased the probability of transmission per act." THE LANCET, Volume 357: Pages 1149-1153, 14 April 2001.
After exposure, the virus invades and replicates in immune cells near the site of infection. It quickly spreads to regional lymph nodes and via the blood stream to the rest of the body. During this stage the patient may experience Acute Retroviral Syndrome, a vague flu-like illness. The patient is often asymptomatic for the first 5-10 years after infection. By that time, untreated, progression to AIDS is inevitable, except in a small subset of patients.
Treatment issues are complicated by issues of poverty and education. In communities with adequate resources, HIV infection is treatable with Highly Active Retroviral Therapy (HAART). This therapy effectively prevents progression to AIDS in many patients, however there are many side effects to treatment, and resistance is a serious issue.
Prevention is an issue complicated by issues of poverty and education. Sexual transmission can be effectively prevented by avoiding sexual contact (abstinence), or by regular, proper use of latex condoms. A large percentage of those infected are unaware of their disease status, which complicates prevention. Spouses are often infected without their knowledge of their partner's status.
Occupational infection can be prevented with the use of universal precautions and by post-exposure prophylaxis.
Currently, no vaccine is available, and it is not clear if a vaccine will be available any time in the near future.
- Gallo RC, Salahuddin SZ, Propovic M, et al. Frequent detection and isolation of cytopathic retroviruses (HTLV-II) from patients with AIDS and at risk for AIDS. Science 1984;224:500-503.
- Bryant ML, Yamamoti J, Luciw P, Munn R, Marx P, Higgins J, Pedersen N, Levine A, gardner MB, Molecular comparison of retroviruses associated with human and simian AIDS. Hematol Oncol 1985;3:187-197.
- Chang SYP, Bowman BH, Weiss JB, Garcia RE, White TJ. The origin of HIV-1 isolate HTLV-IIIB. Nature 1993;363:466-469.
- Wain-Hobson S, Vartanian JP, Henry M, Chenciner N, Cheynier R, Delassus S, Martins LP, Sala M, Nugeyre MT, Guetard D. LAV revisited: origins of the early HIV-1 isolates from Institut Pasteur. Science 1991;252:961-965.
- Hahn BH, Gonda MA, Shaw GM, Popovic M, Hoxie JA, Gallo RC, Wong-Staal F. Genomic diversity of the acquired immune deficiency syndrome virus HTLV-III: different viruses exhibit greatest divergence in their envelope genes. Proc Natl Acad Sci USA 1985;82:4813-4817.
- Levy JA, Hoffman AD, Kramer SM, Landis JA, Shimabukuro JM, Oshiro LS. Isolation of lymphocytopathic retroviruses from San Francisco patients with AIDS. Science 1984;225:840-842
- The Lancet, March 30th 2007
- The Lancet, March 30th 2007
- Guidelines for the Management of Occupational Exposures to HIV and Recommendations for Postexposure Prophylaxis. MMWR Recomm Rep. 2005;54:1-17.
Mandell, Bennett, & Dolin: Principles and Practice of Infectious Diseases, 6th ed., Copyright © 2005 Churchill Livingstone, An Imprint of Elsevier
THE LANCET, Volume 357: Pages 1149-1153, 14 April 2001.
AIDSWEEKLY Plus; Monday, August 9, 1999
THE LANCET, 30 March 2007, reported in The Guardian, 30 March 2007