DETECTION OF CRYPTOSPORIDIUM OOCYSTS AND GIARDIA CYSTS IN THE TISSUESOF EASTERN OYSTERS (CRASSOSTREA-VIRGINICA) CARRYING PRINCIPAL OYSTER INFECTIOUS-DISEASES

The potential cross-reactivity of the combined Cryptosporidium/Giardia direct immunofluorescence antibodies (IFA) of MERIFLUOR(TM) and HYDRO FLUOR(TM)-COMBO tests was examined against tissues containing known de velopmental stages of 12 pathogens causing the principal infectious di seases in oysters. Spores of Haplosporidium nelsoni and Haplosporidium costale produced positive acid-fast stain (AFS) reactions similar in intensity to Cryptosporidium parvum oocysts. Hexamita nelsoni trophozo ites produced positive IFA reactions in both IFA tests; however, the i ntensity of fluorescence was considerably lower and the fluorescein-st aining pattern different than those of Giardia cysts. The applicabilit y of AFS for screening oysters for Cryptosporidium oocysts is low, and positive identification of Cryptosporidium oocysts cannot be accompli shed based on the AFS. Presumptive IFA identification of the Cryptospo ridium oocysts or Giardia cysts in the oyster tissue should fulfill 3 criteria, i.e., bright-green fluorescence of the same intensity as C, parvum oocysts and Giardia cysts in the positive control, correct size and shape of the fluorescein-stained objects, and oocyst or cyst shel l clearly visible.