A single virus particle can be spotted in medical samples by the sound it makes, UK researchers have found. Their method may offer a quick, sensitive technique for detecting viral infections ranging from HIV to foot-and-mouth.
Speedy virus detection can be critical in diagnosing meningitis or monitoring HIV infection. "The quicker you can get an answer the better," says Matthew Cooper at the University of Cambridge whose team has been sounding out viruses
The researchers used quartz crystals, like the wave transmitters in televisions and radios, which vibrate in an electrical field. They coated the crystals - the size of a 5p coin or a dime - with an antibody, to which particles of the human herpesvirus attached.
Increasing the voltage shook the crystal faster until the viruses became dislodged, with an accompanying burst of sound. The vibrating crystal picks up the sound emission like a microphone, and converts it into a burst in the electrical readout. "It's like a rifle or a shot," says Cooper, although the emission is in the same frequency range as FM radio signals and therefore out of our hearing range.
The team hopes that the technique could form the basis of a virus detector to diagnose diseases such as HIV, hepatitis and 'flu. Although it is responsive enough to identify a single virus particle in a tiny liquid drop, it can also detect millions of particles during a rampant infection. However, clinical samples, containing a mix of proteins and other molecules, may be more complicated, cautions Cooper.
There is a need for improved viral detection methods, says microbiologist Donald Jungkind of Thomas Jefferson University in Philadelphia - traditional techniques have their limits. Antibody assays to detect viral proteins have low sensitivity. The alternative, polymerase chain amplification (PCR) to pick up viral DNA, is highly sensitive but laborious and expensive.
Better still, the detector could be taken into the field, adds immunologist Paul Parren of the Scripps Research Institute in La Jolla, California. "It could be built into a more practical machine," he says. Plus, the viral strain could be identified using several strain-specific antibodies, he thinks, so the right vaccine could be prescribed.
Using detectors in the field presents its own problems, a situation brought to light by the recent outbreak of viral-borne foot-and-mouth disease in the UK.
With the outbreak still not completely quelled, rapid virus detection in animals sounds attractive. Currently, skin or blood samples from suspect animals are sent to the Institute of Animal Health laboratory in Pirbright, UK, explains director Chris Bostock, where it can take up to 5 days to reach a verdict.
With such a pressing need for quick diagnoses, " a rapid, accurate and sensitive pen-side test would be helpful," says Bostock.
But, like the field PCR machines awaiting official validation, a future machine using sound detection would have to be decontaminated before being taken from one farm to another, explains Bostock. Ideally, "it has to be disposable," he says.
Central sample processing avoids political issues about access to testing technology. Animals identified using a freely available assay might be discreetly buried, a fear that is creating a certain "reluctance" to embrace simple, rapid technology, says Bostock.