Fig. 7.

Infection status with S. mansoni in field-derived snails (2012–2015), using the PCR assay. 1: B. pfeifferi from Mwea, Mangelete Canal, Kasabong and Mwea. Snails were screened immediately after collection, and 44 of 119 snails not shedding S. mansoni were found positive (prepatent infections). 2: B. pfeifferi from Asao and Kasabong were maintained for at least 32 days after collection and all 143 snails not shedding S. mansoni during that interval were assayed. Those found positive (11) in the PCR assay were assumed to have failed infections. 3: B. pfeifferi from Mwea, 4 months after collection, non-shedders were exposed to S. mansoni and screened 40 days later. Non-shedders were assayed by PCR and those found positive (4) were assumed to have failed infections. 4: B. pfeifferi from Asao infected actively shedding amphistome cercariae, were assayed for S. mansoni. 5: B. sudanica from Carwash and Power House were screened immediately after collection, and all snails not shedding S. mansoni cercariae were assayed by PCR, with 2 showing prepatent infections. 6: B. sudanica from Carwash and Power House were maintained for 32 days and then screened. Any snails not shedding S. mansoni cercariae were assayed by PCR and those found positive were assumed to have failed infections