Scientists have developed a cheap, highly-reliable, instrument-free, point-of-care Zika virus detection test. The sensitivity of the test is very high — the presence of Zika virus can be detected even if the concentration of the virus is as low as 5 plaque-forming units (PFU). For comparison, the amount of Zika virus present in people showing symptoms ranges from 1,000 PFU per mililitre to 10,00,000 PFU/mL.

And results will be known in less than 40 minutes when the dye turns purple. The higher the concentration of the virus in the sample, the quicker will be the detection. The sensitivity can also be increased by using higher sample volume.

“Our system is particularly suitable for resource-poor settings, where centralized laboratory facilities, funds, and trained personnel are in short supply, and for use in doctors’ offices, clinics, and at home,” says a paper published in the journal Analytical Chemistry.

While the diagnostic test can use any of the body fluids — saliva, blood, urine or semen, the researchers tested the sensitivity using only saliva samples. Zika virus is present in higher concentration in saliva compared with blood.  Also, collecting saliva samples is easy, simple and non-invasive. It is becomes particularly important when the testing has to be done on newborns or just-born babies.

The test is specific to Zika virus and will not turn positive to other flaviviruses such as dengue and chikungunya, the researchers claim. This is because Changchun Liu, the corresponding author of the paper from the University of Pennsylvania, U.S., and his co-researchers identified a highly conserved region (hence will not change even when the virus mutates) of the Zika virus that is identical to 19 strains of the virus circulating in the Americas but very different from other common flaviviruses (like dengue and chikungunya).

The Zika virus used for testing the system was obtained from NIAD’s World Reference Center for Emerging Viruses and Arboviruses.

The experiments were carried out at ambient temperature of 18 degree C. Saliva samples from Zika-infected people were not used for testing the sensitivity of the system. Instead, saliva samples were spiked with Zika virus at various concentrations and then tested. The system relies on the heat producing (exothermic reaction) nature of magnesium-iron alloy reacting with water. Thus electricity is not needed to run the test.

The system uses a custom-made “microfluidic cassette that combines viral nucleic acid capture, concentration, and purification”, and also amplification before detecting the virus.

The microfluidic cassette containing saliva spiked with Zika virus is inserted into a chemically heated cup for 40 minutes. If samples contain as little as 5 plague-forming units, they turn purple, which is easily discernible by naked eyes.

While the current demonstration was restricted to qualitative detection of Zika virus, the method can be expanded to include quantification, they say.