Viability and infectivity of oocysts recovered from clams, Ruditapes philippinarum, experimentally contaminated with Cryptosporidium parvum.

This study confirms the important role of marine bivalve molluscs, destined for human consumption, as transmitters of cryptosporidiosis, zoonotic diarrhoeal disease caused by Cryptosporidium parvum. C. parvum oocysts recovered from seawater clams (Ruditapes philippinarum) were viable and infective in five of eight infected neonatal CD-1 Swiss mice. Oocysts were observed in clam gill and gastrointestinal tract tissue homogenates as well as in gill histological sections, by an immunofluorescent antibody technique. In vitro viability of recovered oocysts was also determined using fluorogenic vital dyes (75% viability).