Zika virus has rapidly expanded during the last year in Brazil and currently the outbreaks are occurring in several countries and territories. While following preventive measures is extremely important to limit the spread, finding a reliable field diagnostic test is equally important. And it looks like we got one!
A low-cost paper-based diagnostic test that can quickly diagnose a patient with Zika has been developed by multi institutional team of researchers led by synthetic biologist James Collins, PhD, at the Wyss Institute for Biologically Inspired Engineering at Harvard University. A breakthrough method for embedding synthetic gene networks on portable, small discs of ordinary paper, was already developed in October 2014 by the same group. At that time emerging Ebola virus was used to demonstrate a proof-of-concept color-changing diagnostic test that could screen for the disease. The way the test works is by embedding in paper a synthetic biomolecular sensor designed to detect specific RNA sequences. This rapid diagnostic test was now validated for detection of Zika virus.
They have actually applied complete workflow on paper to detect Zika virus in blood, urine or saliva samples that normally contain very low concentrations of virus. The Zika test consists of a three-step workflow: amplification, Zika detection, and CRISPR-Cas9-aided strain identification. A sample RNA is firstly amplified using a mixture of enzymes and primers. Then a drop of amplified RNA is administered to paper discs that are freeze-dried containing a mixture of cellular components and biological proteins. This leads to activation of the components and change of a disc color which indicates a positive result for Zika virus. This test can be read in a similar way as a home pregnancy test – with a naked eye. However, using specially designed electronic reader the results can be obtained faster and could someday quantify the amount of viral load in a sample.
If the result is positive, in a third step sample is mixed with a freeze-dried CRISPR-Cas9 cocktail and used to wet another set of color-changing paper discs. CRISPR-Cas9, a gene-editing mechanism derived from the immune systems of bacteria, is used to search entire sequences to distinguish between strains whose genetic profiles differ by as little as one nucleotide. Depending on the strain of Zika contained in the sample, these discs undergo another set of visible color changes. Strain information is especially important as some genetic variants may be responsible for different clinical manifestations of infection; e.g. higher incidences of fetal microcephaly and Guillain-Barré syndrome related to the Zika strain found in Brazil (1, 2). It also helps monitoring geographical spread and pathogen linage during epidemic outbreaks.
Using this platform, the researchers have successfully detected Zika virus isolated from infected Vero cells as well as plasma samples from an infected rhesus macaque monkey. They have also tested the system against closely-related strains of the Dengue virus and found that within the first two steps, the system can readily distinguish Zika from Dengue. This way they have demonstrated clinically relevant sensitivity and specificity showing the utility and practicality of this platform technology.
According to Collins, a custom-tailored diagnostic system could soon be used in the field to screen blood, urine or saliva samples. This novel, inexpensive method could help slow spread of Zika virus outbreak, and potentially also other future pandemic diseases as the platform allows rapid development of new sensors for new outbreaks.
If you would like to know more about Zika virus and some latest discoveries check previous Splice articles on Zika virus threat to newborns and the first proof of the association between Zika virus and microcephaly.
By Katarina Kovac, PhD, BioSistemika LLC