Introduction
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 (Fig. 9.1). 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
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 (Fig. 9.2). The progress of the disease has been classified by the US
Centers for Disease Control (Table 9.1). 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 (Fig.
9.2).
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 is likel
Table
9.1 The Centers for Disease Control (CDC)
classification of HIV disease
Transmission
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.
Prevalence
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:
•
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.