Epidemiology of infectious disease: the example of measles.

The situation of unacculturated Brazilian Amazon tribes is described. The isolation of these populations has been sufficiently tight that they have been free of most epidemic diseases of the cosmopolitan world, although diseases associated with persistent infection have a high prevalence. The history of measles epidemics in Amerind populations is reviewed and it is concluded that most deaths can be prevented by basic nursing care but that there is a residual excess mortality characteristic of these populations. Three Brazilian virgin-soil populations and one experienced tribe in Chile, the Mapuche, were vaccinated against measles. Elevated febrile responses were observed in the three virgin-soil populations relative to the fevers seen in the Mapuche and in cosmopolitan populations. Nutritional status, immunological experience, humoral immune response and genetic characters have been examined for an explanation of this phenomenon. The most pronounced correspondence detected so far is a high degree of homozygosity in HLA loci of the virgin populations.