| epidemiology of fasciola hepatica infection in the paraíba river valley, são paulo, brasil. | the study revealed that although lymnaea columella and stenophysa marmorata were found in the same habitat, only l. columella harbored intramolluscan stages of f. hepatica. the population density of l. columella cyclically decreased between september and february, and increased from march to september. the drought that occurred between june and november 1981 dramatically reduced the number of snails collected. larger snails were collected in march-july and november-december, while the smaller sn ... | 1986 | 3564331 |