Intestinal parasites in a rural community of Costa Rica

Abstract

Single stool specimens were collected from 134 residents of Volcán de Buenos Aires, Costa Rica. After brief microscopic examinations in a field laboratory, 108 of the specimens that were sufficient in quantity were preserved in PVA fixative, and/or 10 per cent formalin. Later, the portions in PVA fixative were stained by the trichrome method, and those in formalin were concentrated by the formalin-ether sedimentation technique. The examinations revealed 5 species of helminths and 10 species of protozoa. The effectiveness of the combination of permanently stained film and concentration technique for parasitological examinations was demonstrated by the results obtained on 62 specimens subjected to both procedure. AH of the 62 were positive for intestinal parasites, 36 per cent infected with E. histolytica and 45 per cent with E. hartmanni (small race E. histolytica). Likewise, high prevalences of the common intestinal nematodes were obtained. The examination of permanently stained films from specimens preserved in PVA fixative increased the percentage of recovery of E. histolytica from 28 per cent (by concentration) to 36 per cent. The ability of PVA fixative to preserve trophozoites resulted in the recovery of 14 (23 per cent) infections with D. fragilis in the 62 individulas. The highest prevalence rates of most of the protozoa were in the adult age group, and the highest for the helminths in the children. D. fragilis reached a peak in the 5 to 9' year age group and declined markedly thereafter. To our knowledge, this is the first reported suggestion of the development of age resistance to D. fragilis.