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

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 concentrationsof
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. arabicasnails remain alive to 5‰ NaCl concentration and 100%
mortality occurred at 7.2‰ of NaCl concentration. On the other hand, the
ability of thesnails 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 survive 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. arabicahas
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 appeared to be limited.