Effects of high pressure processing on hatching of eggs of the zoonotic rat tapeworm Hymenolepis diminuta

High hydrostatic pressure processing (HPP) is an effective non-thermal treatment to remove pathogens from a variety of food and food products. It has been extensively examined using prokaryotic organisms but has had limited study on eukaryotic organisms. Treatment using HPP has been shown to be effective in inactivating nematode larvae in food and Ascaris suum eggs. Nothing is known on the efficacy of HPP on tapeworm cysts or eggs. Eggs of important zoonotic tapeworms including Echinococcus and Taenia spp. can potentially contaminate water and food intended for human consumption. The present study examined the efficacy of HPP on the viability of Hymenolepis diminuta eggs. Efficacy of HPP treatment was measured using an egg hatch assay in two experiments. One thousand unhatched H. diminuta eggs in Hanks balanced salt solution were packaged in sealable bags and exposed to 100-600 megapascals (MPa; 1 MPa = 10 atm = 147 psi) for 60s in a commercial HPP unit. Positive (no HPP) and negative (No HPP but frozen/thawed) controls were examined in each experiment. None of the HPP untreated and frozen eggs (negative controls) were able to hatch or exclude trypan blue when placed in the hatching solution in experiment 1 or 2. HPP untreated and nonfrozen eggs (positive controls) hatched and excluded trypan blue; 75\% were positive in experiment 1 and 80\% were positive in experiment 2. No hatched eggs were observed when they were exposed to 300-600 MPa for 60s. Treatment at 400 MPa and above caused rupturing of the oncosphere. Results from this study indicate that HPP is a possible method to inactivate tapeworm eggs and that the susceptibility of tapeworm eggs to HPP is similar to or greater than that of nematode eggs or tissue larvae. (C) 2010 Elsevier B.V. All rights reserved.