Is Planorbarius metidjensis compatible with Schistosoma haematobium and S. bovis?

On the basis of laboratory snail infection experiments it is concluded that Planorbarius metidjensis is unimportant in the epidemiology of Schistosoma haematobium in North West Africa. 410 P. metidjensis Spain were exposed to 8 isolates of S. haematobium from Ghana, Kenya, Madagascar, Mauritius, Morocco, Tanzania, South Africa and Sudan. 50 P. metidjensis Morocco and 50 P. metidjensis Algarve were exposed to S. haematobium Morocco. All infections failed to develop to maturity. Serial sections of P. metidjensis Morocco infected with S. haematobium Morocco at 24 h, 48 h and 72 h post infection showed that 34% of the miracidia penetrated the snail epithelium, but young sporocysts were encapsulated and killed by an ameobocytic host response. Two hypotheses are postulated to explain the reports in the literature that P. metidjensis transmits S. haematobium. The dual infectivity of B. truncatus and B. africanus by S. haematobium from Guinea Bissau suggests that this isolate is probably an infraspecific hybrid with enhanced intermediate host infectivity. By analogy with work on Biomphalaria glabrata and S. mansoni, field observations of P. metidjensis transmitting S. haematobium could be explained if the snail had been previously infected with a compatible digenean, thus rendering a refractory snail into a susceptible snail. S. bovis Spain is compatible with P. metidjensis Morocco, Portugal and Spain with 14.3%, 29.2% and 73.3% of the snails respectively surviving the prepatent period becoming infected. P. metidjensis Spain is refractory to S. bovis Iran and Sudan. Thus, P. metidjensis may be important in the epidemiology of S. bovis in the Iberian Peninsula and North West Africa.