Mixing of Schistosoma haematobium strains in Ghana.

In Ghana, Schistosoma haematobium exists as two strains, one transmitted by Bulinus rohlfsi and the other by B. globosus. In Anyaboni, a resettlement town, where the field station of the UNDP/WHO Schistosomiasis Research and Control Project is located, the residents contract the "rohlfsi" strain of the parasite from the Volta Lake and the "globosus" strain from a stream near the town. The present studies indicate that there is mixing of the two parasite strains on a community and an individual basis. In Anyaboni, the parasite developed well in both B. rohlfsi and B. globosus. In another village 25 km from Accra, where B. globosus was the only vector, the parasite developed well in B. globosus but was refractory in B. rohlfsi. In a village near the Volta Lake where B. rohlfsi was the sole vector, the parasite developed well in B. rohlfsi but was refractory in B. globosus. However, complete separation of the two strains is uncommon in Ghana because extensive mixing has already occurred owing to migration of people and snails.