Histologic Detection of Past Pathogens.

In recent years, histologic methods have been employed for the detection of infectious past pathogens (viruses, bacteria, parasites, or fungi) in ancient tissues. The goal of these palaeopathological studies is to further our understanding of the origin and spread of infectious diseases. Microorganisms can be visualised in preserved ancient tissues after different mummification processes, or in tissue sections from old paraffin blocks. The first step is the examination of paraffin sections with routine staining. Because organisms are often difficult to see in tissue sections, several special stains have been developed to visualise them. However, these histological stains are not specific. Electron microscopy may allow the detection of very small organisms such as viruses; the accurate identification of organisms is in some cases based on a specific morphology at the ultrastructural level. Depending on tissue storage conditions, immunohistological methods such as immunohistochemistry and immunofluorescence allow specific detection of microorganisms if antigenic epitopes are well preserved. [ABSTRACT FROM AUTHOR]