Infectious Agents
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Case Presentation
Electron Microscopy
Discussion
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Electron Microscopy of Infectious Agents

Case I: Cytomegalovirus (CMV) Infection in the Lung

Discussion:

This is a case which I would definitely classify as a needle-in-a-haystack type for electron microscopy because a viral infection was only suspected, and there was no assurance from the broader histologic screening that the sampling for EM would yield target areas with viral inclusions on thin sections.

Our routine screening procedure in situations like this when important ultrastructural features may be widespread or not readily apparent is to first conduct a low-mag scan of the grid, and if that is negative, then to conduct a higher mag scan in a zigzag pattern across the grid, with the assistance of the binocular scope. We will examine the grids over three 30 minute sessions in an attempt to identify diagnostically significant ultrastructure (i.e., organisms, melanosomes, fusiform densities, Birbeck granules, crystals, TRI), and will consider the specimen negative if we find no evidence for the particular feature after the three sessions. I had completed 2 sessions and extended the third session past the 30 minutes, because I still had a couple of bars to screen, when I found the virus infected cell in this case.

We were fortunate with this case to show viruses in the Herpes family even though the histology disclosed no inclusion bodies, and we were not sure we had the haystack, so to speak, in our sampling. The cell we found was literally loaded with viruses and should have been picked up on the toluidine blues. Perhaps we were at the edge of the cell on the thick sections and more of it was included as the thin sections were prepared. This case also points out the need to have a specific screening procedure for cases in which the ultrastructural features may be patchy or scant.

The virus was subsequently identified as CMV in cultures from the lung.

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