A team of U.S. and Canadian researchers has developed a new low-cost method of testing for the Zika virus, which it suggests could be used to quickly identify affected individuals and potentially help curb the spread of infection.
The new method, published online Friday in a paper in the journal Cell, would allow health workers in remote areas to check for the mosquito-borne virus in people's blood, urine or saliva, using a paper test strip, thus eliminating the need for complicated laboratory tests.
These paper-based tests, which detect the virus's genetic material, could be used "on the spot in a matter of hours, so people don't have to wait days" to receive results and be treated, says one of the lead authors of the paper, Dr. Keith Pardee, assistant professor of pharmacy at the University of Toronto.
"When [infected individuals] are bitten by mosquitoes, they become the source for the next round of infections. So if you can in a more timely fashion identify who's sick … it seems reasonable that you'd be able to slow the rate of spread of the virus," he added.
The Zika virus, which is related to dengue and West Nile virus, is primarily spread by the Aedes species of mosquito, but sexual transmission is also possible. The U.S. Centers for Disease Control and Prevention confirmed last month it can cause fetal microcephaly, or babies born with abnormally small heads, and it has also been linked to Guillain-Barré syndrome, which causes the body's immune system to attack nerve cells.
Since Brazil reported its first positive tests for Zika virus last May, the virus has been detected in individuals around the world, including in Canada. To date, Canada has confirmed 67 travel-related cases of the virus, and one locally acquired case through sexual transmission.
Currently, two kinds of tests are used to check for Zika. A polymerase chain reaction, or PCR, test picks up signs of the virus's genetic material ribonucleic acid, or RNA, in blood or urine samples, while a serology test looks for antibodies in blood serum that are created by the body to fight the virus.
According to the Public Health Agency of Canada, a major advantage of a serology test is it can detect antibodies for several months after infection, but it is slow to perform and since the body can produce similar antibodies in reaction to related viruses, a positive result may arise in response to other viruses.
Both existing tests also require samples to be sent to a laboratory, and can take a week or more to get results.
The new method, which researchers tested using blood plasma of an infected macaque, involves three molecular tools, Pardee explains. First, an amplifier in the form of a liquid solution is added to the sample to increase low concentrations of RNA signals of the virus to a level that is detectable. Second, RNA sensors called toehold switches, that are embedded in the test paper, pick up the virus's RNA signals. When the virus is present, they turn the paper a different colour.
The third tool allows for genotyping. It detects tiny mutations in the RNA to determine the lineage of the virus, whether it's American, Asian or African.
"That's important because it's the American lineage that is so worrisome with the really serious side effects," Pardee says.
While the technology is not yet available as a usable testing kit, in the future, the researchers believe staff at local clinics would be able to simply add the amplifier to a patient's blood, urine or saliva sample, wait a couple hours, and then apply a small amount to the test paper. Within 20 to 30 minutes of doing so, the colour of the paper would show the outcome of the test.
Pardee explains there are several advantages to this technology. Because the sensors can be freeze-dried onto paper, the tests can be easily distributed and can be stored at room temperature for as long as a year.
They are also cheap, costing roughly 60 cents to $1 a test to make. Pardee believes this cost could be further reduced when manufactured on a large scale.
And because the RNA sensors are programmable, meaning they can be designed using algorithms to target specific sequences, the technology can be quickly adjusted to test for many other types of viruses.
The research team included scientists from multiple instititutions, including Massachusetts Institute of Technology, Harvard University and Cornell University.