Acquired immunodeficiency syndrome (AIDS)
The human immunodeficiency virus type 1 (HIV-1) is a member of the slow virus (lentovirus) family of retroviruses. It is a distant relative of the human T-cell lymphocytotrophic virus (HTLV)-1 and HTLV-2 viruses which produce some human leukaemia, but is more closely related to nonhuman retroviruses which produce degenerative disease in animals, such as the simian immune deficiency syndrome which occurs in monkeys.
Retroviruses are ribonucleic acid (RNA)-coded viruses that contain reverse transcriptase which transcribes viral RNA into deoxyribonucleic acid (DNA) within the host genome . Viral infection of the host cell may be either latent, where the DNA is integrated but viral replication does not occur, or productive, where RNA and virus assembly occurs. One reason that the host immune system is ineffective at clearing HIV-infected cells is that the proportion of latently infected cells is high in relation to productively infected cells.
HIV-1 has a cell-surface protein (gp 120) which recognises and binds to receptors on several types of human cells. In particular, HIV binds to the CD4 receptor which is carried in high density on the surface of the CD4+ lymphocyte (helper T-lymphocyte). Other reservoirs of HIV infection are macrophages, neural, renal and perhaps epithelial cells.
Effect of immune adsfunction
The extent of depletion in immune function correlates with the loss of CD4+ helper T-cells. However, there is also destruction of dendritic cells, damage to the thymus and immune dysregulation associated with production of autoantibodies and of immune complexes with persistent complement activation. Functional impairment of CD4+ lymphocytes results in disorders of antibody production, delayed hypersensitivity and macrophage function. In addition, secretory immune deficiency occurs in the gut with depletion of immunoglobin A (IgA)-containing jejeunal and rectal plasma cells. This results in a vulnerability to many opportunistic infections, an increased risk of cancer development, and malnutrition due to a reduction in nutrient absorption and metabolism.
Natural history of HIV disease
Following infection by the HIV-1 virus into the blood, there is a brief seroconversion illness which is characterised by flu-like symptoms and lymphadenopathy. There then follows a latent period when the infected subject remains well but which is associated with a progressive fall in CD4+ lymphocyte count . The progress of the disease has been classified by the US Centers for Disease Control . It is expected that 25—35 per cent of those infected will develop acquired immunodeficiency syndrome (AIDS) within 2 years of infection if left untreated. The mortality from AIDS is thought to be 100 per cent. HIV-l viral titres are at their highest during the initial ‘seroconversion’ and the late-AIDS phases of the illness .
The likely period of survival of an HIV-seropositive patient is important in assessment for both emergency and elective surgery. There are three important factors: CD4 (T-helper cell) count, HIV plasma load, and the ability of the patient to receive antiretroviral therapy (HAART).
HIV-seropositive patients die as a result of a wide variety of opportunistic infections caused by the CD4 count falling below a critical level. A low CD4 count is often the best guide to likely clinical events or death within the near future, whereas the plasma viral load (a surrogate for extent of viral production) is the best long-term guide to prognosis — in part because it predicts the rate at which the CD4 count.
The Centers for Disease Control (CDC) classification of HIV diseaseto fall. The likelihood of developing AIDS has been reduced by HAART therapy. This normally consists of at least two nucleoside analogues plus a non-nucleoside reverse transcriptase inhibitor or a proteinase inhibitor. Such therapy is capable of inhibiting all detectable viral replication and clearing the virus from both plasma and lymph nodes. The CD4 count also usually rises dramatically. While the long-term prognosis associated with such therapy is unknown, a pragmatic view would be that the immediate prognosis is likely to be related to whether the patient has further antiviral treatment options available. If so, then even in the face of a low CD4 count and a high plasma load, the patient might live for a considerable period. However, if no further antiviral treatment is feasible, the prognosis is poor and relates predominantly to the current CD4 count level.
The most certain mode of transmission is by transfer of infected blood. The HIV-1 virus is considerably less infective than hepatitis B, and 1 ml of infected blood contains approximately 50 HIV-1 compared with io~ hepatitis B particles. Groups at high risk for acquisition of HIV-1 infection are:
• homosexuals and heterosexuals who indulge in anoreceptive intercourse. The risk of infection increases with the number of partners, associated infections such as gonorrhoea and a history of hepatitis B. Infection may be via traumatic breaches in the anorectal mucosa;
• drug addicts who become infected by using a contaminated needle from an HIV-1 positive source;
• haemophiliacs who receive factor VIII prepared from HIVinfected blood;
• sub-Saharan Africans. In Africa, heterosexual transmission and HIV enteropathy (diarrhoea-wasting syndrome, ‘slim’ disease) are more frequent than in the West. It is not clear whether this is because of different social patterns of heterosexual sex compared with the West or a difference in the infectivity rate of heterosexual intercourse among Africans compared with non-Africans.
More than 250 000 Americans had developed AIDS and a further 1—2 million worldwide were thought to be infected with HIV-1 by 1991. The highest incidence in South America is in Brazil where homosexual transmission, as in the West, is the most significant factor. In the UK over 150 000 persons are thought to be HIV positive, of whom over 5000 have developed AIDS.
Presentation to the surgeon
HIV-positive patients may develop any of the diseases which present to surgeons, and these are normally managed in the same way as in the non-HIV patient while taking special precautions to prevent cross-infection of HIV disease (see below). However, there are some specific conditions which are associated with the HIV disease syndrome and which occasionally require surgical intervention. Areas in which the surgeon may become involved are:
• the management of colorectal and anal disorders including infections and cancer;
• lymph node excision biopsy where there is diagnostic uncertainty;
• the provision of chronic venous access to facilitate chemotherapy for infections (particularly cytomegalovirus retinitis) or neoplasms.
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