A Basic Introduction

AIDS – acquired immunodeficiency syndrome – is a dreadful world epidemic of the 20th century, comparable to the Black Death of the 14th century. The human immunodeficiency virus, HIV, leads to AIDS. When antibodies to HIV are detected, the patient is considered to be infected and is seropositive or HIV positive. The virulence of AIDS and the rate of spread of the epidemic are quite alarming. After the detection of antibodies in the blood, there is a latent period before the end-stage of the disease when the patient exhibits full-blown AIDS. Documented evidence shows that this latent period can be from months to years. In the developed countries, AIDS is primarily associated with the homosexual community, whereas in the underdeveloped regions, the heterosexual spread of the disease is found to be prevalent. The current trends indicate that AIDS is spreading into heterosexual communities of the developed world too.

The reports in the media, journals and international seminars from various countries give a picture of the seriousness and magnitude of the AIDS epidemic. Anderson et al. (1986) made a preliminary study of the transmission dynamics of HIV, the causative agent of AIDS. The epidemiology aspects of HIV infection were again studied by Anderson (1988), giving the variable incubation plus infectious periods and heterogeneity in sexual behaviour. We present two simple models from Anderson et al. (1986) below, which illustrate how mathematical modelling can be used to understand the dynamics of the evolution of AIDS.