Compared to cancer and heart disease, influenza may seem relatively harmless, but it can be fatal, even for the young and healthy. While the exact number of influenza-associated deaths is not known, the Centers for Disease Control estimates the annual numbers could range, depending on the season, from a low four figures to as high as 56,000 (2012-2013) – and that's in the US alone. A swift diagnosis can make all the difference and scientists at the University of Notre Dame have come up with with an easy and novel way to spot the virus: a glow test.

The influenza infection process begins when the virus enters the body and latches onto the cell lining of the respiratory tract. Key to this process are two spikey-looking proteins: hemagglutinin (HA) and neuraminidase (NA). In order for the virus to enter the cell, it must first attach itself to a receptor, which in this case is sialic acid, located on its surface. HA is responsible for this and once the virion has anchored itself to the receptor, it is then taken into the cell via a process known as endocytosis, after which it exploits the host cell's machinery to replicate itself.

The newly formed viral particles that emerge are covered in sialic acid and this has to be removed before they exit the infected host cell to prevent them from clumping together. This is where NA comes in. It is essentially responsible for removing the sialic acid from the particles so they can invade other cells in the body.

The test developed by Bradley Smith and his team at the University of Notre Dame is designed to detect the presence of neuraminidase. If it is present, it means that the patient has the virus and in cases where they have been given an NA-blocking antiviral drug, such as Tamiflu (Oseltamivir) or Zanamivir (Relenza), it means that the prescription has not been effective.

The researchers developed a dye molecule to emit a red fluorescent light when NA is present and a blue one when it is not. In addition to testing for its presence, the test also allows doctors to see whether a prescribed drug is working. As the researchers note in the study, given that the efficacy window for drugs that inhibit NA is within 48 hours of the onset of influenza, it is critical for doctors to be able to quickly confirm a case of infection. On another note, when there is more than one treatment option, the test also helps them determine which drug would deliver better results for the patient.

In experiments, samples containing the dye and NA were combined with both Tamiflu and Zanamivir and illuminated using either a hand-held lamp or blue laser pointer. A red glow meant the drug had failed to shut down the virus, while a blue one indicated the enzyme had been blocked and the patient was in the clear.

"Viral cultures are the gold standard for diagnosis of influenza but take several days to develop," says Smith. "By targeting an enzyme inherent to the virus and identifying its presence in a sample, we can make a rapid determination of the influenza in a patient for an efficient and immediate diagnostic that would improve patient treatment and reduce overuse of antivirals."

While still a work in progress, the researchers believe that with further optimization, the test kit could be developed for use in clinics and in patients' homes. Designed to be low cost and portable – the results of the test can easily be seen by the naked eye so no expensive equipment is required – the researchers say such a kit would not only help improve patient treatment, but also reduce the overuse of antiviral drugs.

That said, given that there are several different strains of influenza virus and that there's always the possibility of new ones emerging, another goal for the researchers is to develop the test further so that it can differentiate between the different classes of mammalian, bacterial and viral NA.

The study was published in the Journal of the American Chemical Society.

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