Cercarial shedding patterns of Schistosoma bovis and S. haematobium from single and mixed infections of Bulinus truncatus.

The cercarial shedding of Schistosoma bovis and S. haematobium were studied in single and mixed infections in the snail host Bulinus truncatus. The two species displayed a distinctive diurnal cercarial emergence with an earlier shedding pattern for S. bovis than S. haematobium (the average emergence peaks were respectively at 0800 h and 1200 h). In mixed infections, each species kept its own cercarial shedding rhythm with no marked alterations. The cercarial emergence pattern is proposed as a new method to identify natural mixed infections in the snail intermediate hosts. The interactions between the two parasites are discussed.

Interference of Echinoparyphium elegans with the host-parasite system Bulinus truncatus-Schistosoma bovis in natural conditions.

Histological observations of Bulinus truncatus naturally infected by both Schistosoma bovis and Echinoparyphium elegans in Sardinia (Italy) have shown that E. elegans is pathogenic to the mollusc and dominant to the schistosome. The larval stages, rediae and metacercariae, acted as compressors. Rediae, mainly the young and very motile ones, also behaved as predators. The organs of the mollusc were variably affected; the ovotestis totally disappeared. The larval development of the schistosome was disturbed; cercariogenesis was strongly inhibited and gave way to high sporocystogenesis. The intensity of this interference depended on the density of echinostome larvae present.

Can tegumental morphology be used as a taxonomic criterion between Schistosoma haematobium, S. intercalatum, and S. bovis?

A comparative study of the evolution in time of the tegumental morphology of male adult Schistosoma haematobium from Niger, S. intercalatum from Cameroon and Zaire, and S. bovis from Spain and Sudan was carried out with scanning electron microscopy. Interindividual, interstrain, and interspecies variations are pointed out. The value of the morphological criterion (tegument with or without spines) is discussed. The tegumental morphology can be used for the identification of schistosome species showing strong phyletic affinities under precise experimental conditions. In the present work, this criterion permits the characterization of strains of S. bovis from Sudan and Spain.

[Comparative analysis of the rhythm of cercariae emergence in three strains of Schistosoma bovis (trematoda: Schistosomatidae)]. / Analyse comparative du rhythme d'emission des cercaires de trois souches de Schistosoma bovis (Trematoda: Schistosomatidae).

A comparative experimental study of the rhythmic shedding of three geographic strains of Schistosoma bovis cercariae (Sardinian, Sudanese and Spanish) by Bulinus truncatus showed a significant difference in the emergence patterns. The results support the existence of a genetic variability of the emergence rhythms. The origin of the variability is discussed and could be found in the pastoral practice and the ecological characteristics of the different transmission foci.

Genetic variability of Schistosoma bovis cercarial production according to miracidial dose.

Cercarial production related to miracidial dose variation with Schistosoma bovis strains from Sudan and Spain in Bulinus truncatus from Tunisia was studied. Results showed that an increase in the miracidial dose proposed to the host-mollusc (1 and 5 miracidia) gave rise to a decrease in cercarial productivity of Sudanese S. bovis and to an increase for Spanish S. bovis. It is concluded that this response difference to the miracidial dose variation depends on genetic characters peculiar to the parasite strain and represents a new aspect of genetic variability of schistosome populations.

Schistosoma bovis: patterns of cercarial emergence from snails of the genera Bulinus and Planorbarius.

A comparative experimental study of the rhythmic shedding of two geographic strains of Schistosoma bovis cercariae by Bulinus truncatus and Planorbarius metidjensis did not show any differences in emergence patterns. In our opinion, the results support the hypothesis that cercarial emission rhythms are determined primarily by the parasite in these snail/parasite associations.

[Development of the sporocysts of Schistosoma bovis after microsurgical transplantation in Bulinus truncatus]. / Evolution des sporocystes de Schistosoma bovis après transplantation microchirurgicale chez Bulinus truncatus.

Microsurgical transplantations of Schistosoma bovis daughter sporocysts to uninfected Bulinus truncatus leads to a dedifferenciation of transplanted sporocysts producing an additional generation of daughter sporocysts. These ones settle into the whole digestive gland and produce infective cercariae. For all the parasitosis, a part of the daughter sporocysts born from the transplanted ones, remains in the head-foot region and are in their turn responsible for an active sporocystogeny. Data demonstrate that the cercarial production dynamics is at least in part in relation with the intramollusc dynamics of sporocyst populations. Success of microsurgical transplantation of S. bovis sporocysts permits cloning perspective of this species.