Effect of Freezing and Boiling on the Infectivity of Third-Stage Larvae of Angiostrongylus cantonensis Present in Land Snails and Freshwater Prawns

Abstract

Third-stage larvae of Angiostrongylus cantonensis recovered from land snails (Achatina fulica) and freshwater prawns (Macrobrachium rosenbergi) which had been exposed at 0 C for 24 hr were found infective when fed to rats. The larvae, however, were not infective when recovered from snails or prawns which had been exposed in a freezer for 12 or 24 hr at -15 C. Some of the larvae recovered from snails that had been boiled in water for 1 min were infective to rats, but larvae recovered from snails boiled for 2 or 3 min or from prawns boiled for 1 min were not infective. The thermal death point of the third-stage larvae in water has been found to be somewhere between 50 and 55 C. Reports indicate that in some areas of the Pacific Islands and Southeast Asia, certain species of freshwater prawns (Macrobrachium sp.) and snails (Pila ampullacea) used as food are frequently infected with third-stage larvae of Angiostrongylus cantonensis and are believed to serve as major sources of human infection with this parasite (Alicata and Brown, 1962; Punyagupta, 1965). Since freezing or boiling would appear to constitute a simple and practical method of destroying the vitality of the infective larvae present in snails or prawns, experiments were conducted to determine the efficacy of these methods in rendering these infected invertebrates safe as food, as far as it concerns cerebral angiostrongylosis. Even though the species of snails and freshwater prawns used in the present study are not necessarily the same as those used for food in Angiostrongylus endemic areas, it is believed that the results obtained would be generally applicable to other species of snails or prawns, or other animals of approximately the same