HIV/AIDS: the first 25 years--a view from Nairobi.

HIV infections are zoonoses occurring in communities that hunt chimpanzees (HIV 1) and sooty mangabeys (HIV 2) in the forests of equatorial and West Africa respectively. Most cross species transmission to man probably fizzles out, but the transmission of HIV 1 type M around 1930 eventually resulted in a pandemic that has spread around the world. HIV 2 types A and B have caused epidemics in West Africa. HIV infections are characterised by three phases (i) an initial, primary infective phase with rising viraemia, asymptomatic and silent, lasting for some 10 weeks, (ii) a long quiescent phase with the viraemia and illness mostly held in check by the immune response and lasting some 10 years in HIV 1 and 20 years or so in HIV 2 and (iii) a terminal third phase lasting some 10 months with rising viraemia, falling CD4 levels and multiple opportunistic infections recognised in a community by the onset of a florid AIDS epidemic. The silent primary epidemic reached Nairobi around 1980, with the florid secondary AIDS epidemic peaking here around 1992 and overwhelming the hospitals and other health services. The introduction of highly active antiretroviral therapy (HAART) has dramatically improved the prognosis for individual patients with AIDS, but it has been education and a changing attitude to condoms that has led to a progressive fall in incidence, so that the worst of the epidemic may now be over. Modifying the immunological response during the quiescent phase with the hope of prolonging this phase indefinitely may be the way forward for those who are already infected. Steroids have been shown to have a possible role here rather than anti-retroviral drugs (ARVs) which are not curative and prone to the development of drug resistance. Limited personal experience suggests that steroids may also have a role in salvaging critically ill AIDS patients, who need to be treated as emergencies. With an educated public and attention to alternative routes of infection such as blood transfusion, the epidemic should be increasingly contained during the next 25 years, and may even fizzle out.