Although treatable, respiratory syncytial virus (RSV) results in the deaths of over one million children annually as its late detection renders antivirals ineffective. Now US researchers have created a tool to detect small amounts of the virus simply and quickly.

David Wright's group at Vanderbilt University, Nashville, has developed a probe that can detect RSV RNA in infected cells with approximately 200 times greater sensitivity than existing techniques, potentially making early diagnosis of infection possible. 

Wright's method is adapted from existing filament-based antibody recognition (FARA) assay technology. FARA uses probes consisting of a polyester filament with antibodies for specific pathogens bound to its surface. When the filament is exposed to infected cell lysates, the antibodies bind to the pathogens in the sample. The filament-pathogen complexes can then be analysed using fluorescent reporters, allowing pathogen detection. Wright's probe avoids the need for the separate analysis step by incorporating its own fluorescent reporter.  

Unlike FARA filaments, the new probe's filament is gold clad and, rather than being bound to antibodies, is attached to one end of a length of DNA that has a fluorophore at the other end. The DNA is complementary to a repeated sequence found exclusively in RSV RNA. In the absence of this RNA, the DNA adopts a hairpin conformation, bound to itself, which brings the fluorophore and the gold filament close together. The gold acts as a quencher, preventing the fluorophore fluorescing. When the probe is exposed to RSV RNA in infected cell lysates, it opens into a straight conformation to bind the viral RNA. This creates distance between the fluorophore and the gold filament quencher, resulting in fluorescence.

Wright suggests that advantages over existing viral detection methods could make widespread implementation of the beacon a real possibility. 'Most gold standard approaches [for example culturing the virus or amplifying its DNA using a polymerase enzyme] take anywhere from one to four days in a clinical setting,' he says. 'We are hoping that the proven processing capability of this technology will significantly reduce this time. Additionally, the results demonstrate a sensitivity and ease of use that one day may make the platform amenable to point of care applications.'

Jenny Handforth, a general paediatric consultant, who is an expert in infectious diseases at the Mayday Hospital, Croydon, UK, agrees. 'If the potential for simplification is realised, then coupled with the sensitivity data this could be an exciting tool,' she says. 'Of course, its usefulness needs to be shown in clinical samples,' she adds. 'If such results are demonstrated then it could become an important adjunct in RSV infection diagnosis.'

Katie Dryden-Holt 

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