Influence of desiccation on the survival of Bulinus globosus under laboratory conditions

Environmental changes are generally known to influence the distribution and abundance of schistosome intermediate host snails (IHs). However, the influence of hydrologic changes per ser on the length of survival of schistosome IHs is not fully understood. To explore how desiccation may influence the survival of Bulinus globosus, the main IHs of Schistosoma haematobium in southern Africa, we conducted a study under laboratory conditions where snails were subjected to periods of desiccation and their survival evaluated. Desiccation period from 28 to 49 days post-draining of water was associated with an increase in mortality of 33.2 and 42.4% in large (mean shell height 7.81 +/- 0.44 mm) and small (mean shell height 5.94 +/- 0.68mm) B. globosus snails, respectively. Although the duration of desiccation had no effect on the depth of burrowing, large size snails burrowed deeper into the soil than small size snails. The LT50 and LT90 of snails designated as large (7.81 +/- 0.44mm) were 73.35 +/- 10.32 and 110.61 +/- 21.03 days, respectively. On the other hand, LT50 and LT90 for snails designated as small (5.94 +/- 0.68mm) were 59.64 +/- 8.56 and 84.19 +/- 12.09 days, respectively. The survival of B. globosus during desiccation depended on the size/age of the snail where large size snails aestivate and survive for a longer period by burrowing deeper into the soil. We therefore conclude that adult B. globosus may play a significant role in habitat recolonization after a period of drought which is a common phenomenon in schistosomiasis endemic areas when population crashes.