Effect of salinity and drought on the survival of Biomphalaria arabica, the intermediate host of Schistosoma mansoni in Saudi Arabia

Abstract

The effect of salinity and drought as two important abiotic factors on the survival of Biomphalaria arabica, the intermediate host of Schistosoma mansoni in Saudi Arabia was studied in the laboratory. Saudi B. arabica snails were collected from freshwater bodies in Abha, Asser district, Saudi Arabia. Snails were exposed to ten concentrations of Sodium Chloride as follow: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10‰. In addition, snails were exposed to a series of Sodium Chloride concentrations lie between the concentration that produced 100% mortality and the concentration lies previous to it. In drought experiments, the snails were exposed to complete dryness for 12, 24, 36 and 48 hours and the snails in moist soil were examined daily for fifteen days. The results revealed that B. arabica snails remain alive to 5‰ NaCl concentration and 100% mortality occurred at 7.2‰ of NaCl concentration. On the other hand, the ability of the snails to resist the complete dryness appeared to be limited, since 100% mortality was achieved after 36 hours in absence of lettuce leaves and after 48 hours in the presence of lettuce leaves . The snails in moist soil provided with fresh lettuce leaves remain surv ive to 15 days without any death. In the case of snails in the moist soil without fresh lettuce leaves, the survival was unaffected until 10 th day post-exposure, while further increases in exposure period resulted in reductions in survival up to 50% for snails exposed for 15 days. The present investigation declared that B. arabica has a great resistance to salinity increase and this may be explain why B. arabica has a great abundance in KSA. However, the ability of B. arabica snail to resist the dryness app eared to be limited.