Lack of detection of influenza genes in archived formalin-fixed, paraffin wax-embedded brain samples of encephalitis lethargica patients from 1916 to 1920.

A method was developed for detection of influenza genes in formalin-fixed brains of mice that had been experimentally infected with influenza A/NWS/33 (H1N1) virus. Using this technique, messenger ribonucleic acid (mRNA) of the beta-actin gene was detected in eight clinical brain samples from the 1916-1920 outbreak of encephalitis lethargica, showing preservation of particular mRNAs. However, we did not detect influenza nucleotide sequences of M, NP, and NS genes from these same samples. We conclude either that influenza was not the causative agent of encephalitis lethargica or, possibly, that the virus had a hit-and-run mechanism and was no longer present in the brain at the time of death of the patients.