Introduction

The human immunodeficiency virus (HIV) is the aetiological agent of the acquired immunodeficiency syndrome (AIDS). Despite intensive research during the past 9 years since the discovery of the virus, the epidemic continues to spread in the human population. Analysis of epidemiological data reveals a depressing picture for the worst afflicted regions such as sub-Saharan Africa, with increasing amounts of infection in the heterosexual population. In these regions it is likely that AIDS may result in population decline within a few decades if present trends continue (Anderson et al. 1991, Anderson and May 1991).

The course of HIV infections can be separated into three stages.

1. Acute clinical illness during primary HIV infection occurs in 50-70% of infected patients, starts generally 2-4 weeks after infection and lasts from 1-2 weeks (Tindall and Cooper 1991). The clinical manifestations are varied and include fever, neuropatic and dermatological symptoms. Virus can be isolated from infected blood cells, cell free plasma, cerebrospinal fluid and bone marrow cells. The high replication and widespread distribution of virus is followed by strong immunological responses, which result in a decrease of viral antigens to almost undetectable levels and a resolution of clinical symptoms.

2. The second, chronic, phase (8-10 years on average) is characterized by low levels of HIV expression and only small pathological changes. Patients are generally asymptomatic. CD4 cell concentrations are constant or slowly decreasing.

3. […]