Freshwater snails are intermediate hosts of various trematode diseases. In Zimbabwe extensive work has been done on schistosomes and their intermediate hosts. Little or no information is however available on the abundance, diversity and host relationships of other trematode species. Information on ecology and population dynamics of snails other than the intermediate hosts of schistosomes is also lacking. It is important to study the ecology and population dynamics of snail hosts in order to fully understand the epidemiology of snail borne diseases. This help in identifying potential and actual transmission sites and important transmission periods so that control programs can be done cost effectively. It is also important to identify snail intermediate hosts correctly as this permits both potential and actual foci of transmission of snail borne diseases to be well defined. Morphological characters which are often used in snail identification are confounded by environmental factors. The morphological techniques need to be complemented by molecular techniques to enable correct identifications.

The snail fauna in the study area was dominated by intermediate hosts of trematode parasites of medical and veterinary importance. The seasonal fluctuations in snail densities were variable but generally, low densities were recorded during the rainy period due to flushing out of snails by floods and high densities were recorded in the post rainy period when habitats stabilized. Except for rainfall, ecological factors did not markedly influence the observed seasonal trends.

Out of 13,789 snails collected 916 (6.6%) harbored patent trematode infections. No double infection was recorded. The following cercaria types were recorded from the study sites: Schistosoma, amphistome (pigmentata type), echinostome, xiphidiocercaria, strigea, vivax, ophthalmo-xiphidiocercaria and brevifurcate apharyngeate monostome cercaria (BAM). The echinostome was the most common type of cercaria recovered, contributing 38.2% of all infections. The amphistome cercaria contributed 37.6% and Schistosoma infections contributed 8.0% of all the infections.

The main intermediate host for amphistomes was B. tropicus. Infections of B. globosus, Biom. pfeifferi and B. forskalii with amphistomes are new records for Zimbabwe. Dual infections of C. microbothrium with either S. haematobium or S. mattheei could not be established in this study.

The taxonomic status of the B. truncatus/tropicus complex from Plumtree area was examined by using morphometric analysis combined with RFLP and RAPD data. Despite the variation in shell form observed, RFLP and RAPD data indicate that the populations are not genetically distinct and hence represent a single taxon, B. tropicus.

Future work should involve clarifying the taxonomic status of the amphistome and the other cercaria morphological groups that were recorded in this study. It will also be necessary to determine the definitive hosts of the various trematode parasites and to explore whether the lack of double infections in this study was due to spatial and temporal effects or was due to trematode antagonism, in order to identify trematode species that have the potential to be used as biological control agents for schistosomiasis and amphistomosis.

In conclusion, the seasonal variation of snail species was variable and was mainly influenced by rainfall. There is diversity of larval trematode parasites in snails in the highveld and lowveld areas of Zimbabwe.