We conducted monthly snail captures in Bananal, State of
São Paulo, Brazil, between March 1998 and February 2001, to identify
Schistosoma mansoni
vectors, estimate seasonal population changes, and delimit foci. We also
evaluated the impact of improvements in city water supply and basic sanitation
facilities. We identified 28,651 vector specimens, 28,438 as
Biomphalaria tenagophila
, 49 of them (0.2%) infected with
S. mansoni
, and 213 as
B. straminea
, none of the latter infected. Vectors predominated in water bodies having
some vegetation along their banks. Neither population density nor local
vegetation could be linked to vector infection. We found the first infected
snails in 1998 (from March to May). Further captures of infected snails
ocurred, without exception, from July to December, when rainfall was least.
Irrespective of season, overall temperature ranged from 16.5ºC to 21ºC;
pH values, from 6.0 to 6.8. Neither factor was associated with snail population
density. Frequent contact of people with the river result from wading across
it, extracting sand from its bottom, fishing, washing animals, etc. Despite
a marked reduction in contamination, cercaria shedding persists. Whatever
the location along its urban course, contact with river Bananal, particularly
of the unprotected skin, entails risks of infection.
