Answer to Case 477

Answer: ciliated respiratory epithelial cells. These are a common parasite mimic, especially when seen in unfixed wet preparations, since the cilia remain motility for quite some time after being exfoliated from the respiratory mucosa. It is important to note that these are NOT parasites. Unfortunately there are several reports where these are misidentified as Lophomonas blattarum; however, L blattarum is a parasite found in various arthropods and is NOT thought to be a human parasite. 

You can easily identify ciliated epithelial cells by their small size and characteristic shape. Note that the cilia are present in a dense band at the apical surface:

You can really appreciate the columnar shape of the cells in this case.

It can be even more challenging when the ciliary tufts become detached (called detached ciliary tufts/DCTs or ciliocytophthoria). I've featured this multiple times on my blog in the past and have described how to differentiate ciliated host cells from other microorganisms. Check out these past posts for more information:

Case 396
Case 369
Case 283
Case 262

Thank you all for writing in!