An in-vitro test for assessing the viability of Ascaris suum eggs exposed to various sewage treatment processes

Abstract

A simple procedure using Ascaris suum as a model for Ascaris lumbricoides in testing the ability of sludge treatment processes to kill the eggs of parasitic roundworms was developed. Unembryonated and embryonated A. suum eggs were placed in a mesophilic anaerobic sludge digester or a sludge lagoon, or stored at 4°C. Unembryonated eggs were recovered and incubated at 32.5°C and 90–95% r.h. for 48 h and viable eggs developed embryos consisting of two or more clearly defined cells. This viability was confirmed by further incubation for 30 days, when motile first-stage larvae were seen. Infectivity was demonstrated by administering larvated eggs to worm-free pigs and recovering adult worms from the small intestine at necropsy. After 1 week in a mesophilic anaerobic digester, 95% of A. suum eggs produced two-cell larvae in vitro, with 86% progressing to motile larvae. After 5 weeks in the digester 51% progressed to motile larvae. Between 42% and 49% of eggs stored in a sludge lagoon for 29 weeks were viable and able to develop motile larvae. In the case of eggs that were embryonated before treatment, >98% survived up to 5 weeks in the digester and were able to develop motile larvae. More than 90% of embryonated eggs survived for 29 weeks in the sludge lagoon and were able to develop motile larvae.