Environmental parameters influencing the distribution of parasite species in three neighbourhoods of differing socioeconomic conditions in La Plata, Argentina were analysed. Coproparasitological screenings were performed in children up to 14 years old from a marginal zone (100), a suburban neighbourhood (101), and an urban area (91) in 1999--2000. The presence of parasite species in environmental samples (water and soil) and the degree of association among parasite communities was documented and evaluated. The prevalence of infection in each population was 73.0%, 54.4% and 35.2%, respectively. The frequencies of helminths and pathogenic protozoa were both higher in the marginal zone, where sanitary and environmental conditions were significantly inferior compared with the other zones. The high prevalence of intestinal parasites in this infantile population was related to parasitic contamination of the soil and water sources in addition to deficient sanitary and sociocultural conditions. Calculation of an equitability index revealed that the specific richness was less equitable once socioeconomic conditions and hygienic practices were improved. This study demonstrates the need to implement management practices for the control of intestinal parasitoses in accordance with the environmental and sociocultural characteristics of a given ecosystem.

Intestinal parasite infestation in indigenous Mbyá-Guaraní communities in Misiones, Argentina, was IntroducciónLas parasitosis intestinales y la contaminación fecal representan un importante problema que enfrenta la salud pública y ambiental en los países en vías de desarrollo 1,2 . Estas infecciones son generalmente subestimadas por ser asintomáticas, pero sus efectos pueden contribuir a la morbilidad cuando están asociados a la malnutrición 1 . En la mayoría de los casos se cuenta con datos de prevalencia fragmentarios, procedentes de niños en edad escolar o de hospitales, que no son representativos del total de la población en un área determinada 2 . Si bien existen estudios de campo desarrollados en diferentes poblaciones, no han sido utilizados en la elaboración de medidas preventivas, ni han sido devueltos a las poblaciones involucradas, de manera que participen en la búsqueda de alternativas para la protección de la salud 1,2 .El efecto del cambio cultural y la degradación ambiental en la prevalencia de infecciones parasitarias ha sido estudiado en poblaciones indígenas americanas 3,4 . Fitton 4 sostuvo que los procesos de colonización y de explotación de los recursos naturales han contribuido a la progresiva aculturación de poblaciones indíge-nas de Ecuador. Esta situación, unida al sedentarismo y la deficiente atención de la salud, favoreció la transmisión de infecciones parasitarias en esas poblaciones 3,4 . Por otra parte, también las infecciones parasitarias causan o agra-

The influence of temperature and humidity on the survival and development of Toxocara canis eggs in an in vitro model system was investigated. Two soil samples were inoculated with T. canis eggs and maintained at 3% and 50% humidity and temperatures of 19-24 degrees C. Nine soil samples were inoculated with T. canis eggs of which three samples were kept at 4 degrees C with humidities at 3%, 15%, and 30%; three were maintained at 21 degrees C and three more were incubated at 34 degrees C, and at the same three humidity levels. Samples were monitored every 7 days for a total of 2 months, for the presence and development of eggs. With increasing temperature, the number of eggs undergoing development increased (P<0.01); the number of deformed eggs decreased, the number of infective eggs increased (P<0.01), and egg maturation was accelerated. A decrease in the survival of infective eggs occurred at 34 degrees C. An increase in humidity produced a rise in the number of developed eggs at all three temperatures (P<0.01). This study suggests that elevated temperatures accelerated the development as well as the degradation of eggs of T. canis, whereas the range in humidity was directly correlated with egg development.

The great number of cases of multiple infestations seen among suburban as well as rural populations calls for special attention and underscores the need for more extensive epidemiological studies that take on the different aspects of this complex issue with the goal of implementing more efficient health initiatives and programs.