The correct answer is A, UV fluorescence microscopy.  Cryptosporidium appears to be the only coccidian genus identified thus far that does not exhibit marked autofluorescence of the oocyst wall.

Click here to open a new window with images of Cryptosporidium parvum oocysts stained with modified Kinyoun's acid-fast (answer B) or with the fluorescent stain auramine-rhodamine (answer C).  Click here to open a new window with more information about enzyme immunoassays for the diagnosis of cryptosporidiosis.  Close the new window to return to this page.