Molecular characterisation of emerging pathogens of unexplained infectious disease syndromes.

Introduction: The discoveries of HIV and Helicobacter pylori in the 1980s were landmarks in identification of novel pathogens causing unexplained infectious syndromes using conventional microbiological technologies. In the last few decades, advancement of molecular technologies has provided us with more robust tools to expand our armamentarium in this microbial hunting process. Areas covered: In this article, we give a brief overview of the most important molecular technologies we use for identification of emerging microbes associated with unexplained infectious syndromes, including 16S rRNA and other conserved targets sequencing for bacteria, internal transcribed spacer (ITS) and other target gene sequencing for fungi, polymerase and other gene sequencing for viruses, as well as deep sequencing. Then, we use several representative examples to illustrate how these techniques have been used for the discoveries of a few notable bacterial, fungal and viral pathogens associated with unexplained infectious syndromes in the last 20-30 years. Expert opinion: In the past and present, characterization of emerging pathogens of unexplained infectious disease syndromes has relied on a combination of conventional culture- and phenotype-based technologies and nucleic acid amplification and sequencing. In the next era, we envisage more widespread adoption of next generation technologies that can detect both known and previously undescribed pathogens.