Electron Microscopy of Infectious Agents

Infectious Agents

Case 1
Case 2
Case 3
Case 4
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Introduction

I have selected a series of 8 infections studied by electron microscopy for this Case of the Month format, and divided them into two groups. Group 2, which features viral infections, is included here. Cases 1-4, of Group 1, which featured protozoan and fungal infections, were presented in August 98.

This series of cases selected is not intended to be all-inclusive, and is only a brief treatment of some of the more unusual examples of virus infections that may be referred for electron microscopic review. Jan Orenstein has written an excellent paper on the role of electron microscopy in infections disease diagnosis, and I would encourage you to read his paper ( J. Histotechnol 18:211, 1995) for a more in-depth treatment of the topic.

In our facility, microbiological specimens are too infrequently submitted, and represent only about 0.2% of our total. This is a shame because EM can be very useful in identifying the virus and providing a very definitive documentation of the agent. On the other hand, the percentage of microbiological cases with positive findings is relatively small, so I can understand why the clinician may be reluctant to take the additional step of having EM studies performed when other tests may have more specificity. Here, I think, is where the Pathologist plays a critical role by working with the clinician to recommend EM studies where appropriate, and to discourage the clinician when indications suggest that EM studies would have little or no yield. In addition, the Pathologist can advise/assist the clinician on the most suitable specimen selection and ensure proper handling for optimum results. Equally important when the specimens are submitted without consultation, the Pathologist can correlate the histology samples with the tissue selected for EM to ensure that the infected areas are likely to be included in the EM sample. This may avoid the needle-in-the-haystack phenomenon or, at least, improve the probability that the haystack is included in the EM specimen.