Distribution and preservation of Schistosoma mansoni eggs in stools.

Thirty-eight stool samples were preserved with sodium azide, 5 mg g-1 of stool. Results show that after 12 weeks, all the samples with S. mansoni eggs remained positive with good egg morphology. Egg counts show an average decrease of about 20%. Given the logistic advantages provided by using a small quantity of dry preservative this method is acceptable for mass prevalence surveys where sensitivity is not critical. The distribution of eggs in the stool was studied in 10 samples. Results showed no significant differences between centre and surface of the stools.