Stool survey and egg isolation
All stools samples collected from participants were weighed, and single
slides prepared as previously described (Katz et al., 1972). On the
following day, the slides were read, and the number of schistosome eggs
per gram and the presence of other helminths were recorded. Stools
positive for S . mansoni were homogenized in a blender with
200 mL of 2% saline solution and then processed through a series of
metal sieves and nylon filter bags (300 µm - 55 µm mesh pore size, FSI,
Michigan City, Indiana, USA) and gravity sedimentation to concentrate
the eggs (Dresden and Payne, 1981). The bottom 5 mL of sediment was
collected and then kept frozen at -20 °C for DNA extraction. In
accordance with Brazilian Ministry of Health guidelines (Ministério da
Saúde do Brasil, 2014), participants with one or more egg-positive
stools samples were given a one-time dose of praziquantel (60 mg/kg for
children 4 to 15 years old and 50 mg/kg for adults), and 4–6 weeks
later three follow-up stool examinations were performed on those
treated. For other helminthiases a single dose of albendazole was
provided (FigureS1).