Introduction It is known that several viral species can induce parkinsonism in animals and humans, but no specific virus has been discovered in the classical human form of PD.

Methods To investigate this further, we used next generation sequencing (NGS) to analyse post-mortem transcriptomes of substantia nigra (SN) and olfactory bulb (OB) in four PD cases and four multiple sclerosis patients who acted as positive controls. Bioinformatic analysis of the data set removed the majority of human transcripts and the remaining sequence data were compared to existing viral sequence data sets to search for signature viral sequences.

Results Despite high read numbers and good quality NGS data, no viral or bacterial transcripts could be identified from either of the tissues examined. The few matches to existing viral databases were to viruses which rarely, if ever, infect humans and no multiple hits (matches to more than one gene of the same virus) were observed. Similarly, no bacterial sequences were found although it should be noted the analysis was carried out at the mRNA level.

Conclusion This small but detailed analysis provided no evidence of RNA viral signatures in the OB or SN in the four samples taken from Parkinson’s disease brains. It is still possible that other brain areas known to display Lewy body pathology may contain viral sequences.