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A cross-sectional study of soil-transmitted helminthiases in the Northern Bolivian Altiplano was carried out over the 6-year period 1992-97. Prevalences, intensities and associations were analysed from coprological results obtained in 31 surveys (28 in schools and 3 in individuals of all age-groups) performed in 24 Aymara communities located between the city of La Paz and Lake Titicaca, at an altitude of 3800-4200 m. Ascaris lumbricoides and Trichuris trichiura were detected, with local prevalences in the range 1.2-28.0% and 0.0-24.0%, respectively. Significant differences in prevalence rates of trichuriasis were detected, with highest prevalences in male schoolchildren and in subjects aged > 40 years. The global intensity ranged from 24 to 86,544 eggs per gram of faeces (epg) and from 24 to 4560 epg for ascariasis and trichuriasis, respectively. Higher intensities were noted in girls. A. lumbricoides egg counts were statistically significantly higher in the 5-8-years age-group. A positive association between A. lumbricoides and T. trichiura infections was detected. The proportion of heavy infections for A. lumbricoides was 0.1% and 1.0% in the school and community surveys, respectively. No heavy infection for T. trichiura was detected. The very high altitude and its severe environmental conditions may determine the relatively low prevalences and intensities in this area.

Over a 6-year period, an epidemiological study of human infection by Fasciola hepatica in the Northern Bolivian Altiplano was carried out. Prevalences and intensities were analysed from coprological results obtained in 31 surveys performed in 24 localities and proved to be the highest known so far. The global prevalence was 15.4%, with local prevalences ranging from 0% to 68.2%. Significant differences between prevalence rates were detected and the highest prevalences were in subjects aged < 20 years. However, prevalences showed no gender difference. The global intensity (eggs per gram of faeces, epg) ranged from 24 to 5064 epg and showed arithmetic and geometric means respectively of 446 and 191 epg, with highest local arithmetic and geometric means of 1345 and 678 epg. Significant differences in mean egg output were detected between localities. The significantly higher F. hepatica egg counts shown by girls in school surveys is worth mentioning. Although the distributions of intensities according to age-groups did not show any significant difference, a decrease of egg output counts with an increase of age was detected. It is concluded that fascioliasis is a very important human health problem in this region.