Introduction

There is a perception that the demographic impact of infectious disease is largely determined by the mortality associated with pandemics or the death of children caused by infections early in life (Murray and Lopez, 1997), but infectious diseases can also reduce the birth rate through their impact on fertility (Weisenfeld and Cates, 2008). Widely spreading epidemics of fatal infections can cause sudden population declines. The ability of populations to recover from such shocks depends upon whether these are transitory epidemics or whether endemic spread leads to a continued heavy toll (Garnett and Lewis, 2007). The great mortalities like the Black Death and Spanish Influenza have been associated with directly transmitted infections which can spread widely. Infections such as measles, malaria and diarrhoeal disease, which cause many infant deaths in poorly nourished populations, have a high incidence in the young with common exposure caused by direct transmission or transmission via water or insect vectors. Apart from some intrauterine mortality associated with infections like tuberculosis and malaria (Mayaud, 2001), the infections generally associated with reductions in fertility are more restricted to a sexual route of transmission. That reductions in fertility are caused by sexually transmitted infections can be explained by their association with the genital and reproductive tract. The demographic impact of the reductions in fertility associated with these infections is less widely recognised than that associated with mortality because sterility and early pregnancy loss are less noticeable events. Nonetheless, reduced fertility can potentially greatly alter demography.