In today’s pandemic-ravaged world, waking up with a mild cough or slight fever can be both hugely worrying and massively disruptive. With symptoms as non-specific as these, the only way to determine whether the sufferer has a common cold or full-blown Covid-19 is to run a diagnostic test. With countries now looking to relax lockdown periods and social distancing measures as soon as possible, the need to test for Coronavirus infections quickly, cheaply and at scale has never been more urgent.
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Luckily, help may be close at hand, in the form of a new test based on gene targeting technology known as CRISPR. According to researchers, the low-cost respiratory swab test can diagnose Covid-19 infections in about 45 minutes and requires no specialized equipment. Thanks to a greatly accelerated development timeline, the test could soon support scaled-up Coronavirus testing regimes across the world.
Dr. Charles Chiu of the University of California, San Francisco School of Medicine, who is leading the development of the new test in collaboration with scientists at Mammoth Biosciences, sees the new diagnostic as a potential game-changer. He said:
“This is the first CRISPR-based diagnostic test for Covid-19 infection. I see it as a viable alternative to the commonly used RT-PCR based tests that are currently available.”
Strengths and Weaknesses
Most current Covid-19 tests are based on reverse transcriptase polymerase chain reaction (RT-PCR), which boasts specificity and sensitivity rates of 90 percent and above. The downside is that the test can only be performed in well-equipped labs, which means the minimum test time is usually around 4 hours, and can be far longer. With PCR testing taking place on a huge scale, the reagents used in the test are also in short supply. Charles Chiu said:
“Compared to other tests that directly detect the Coronavirus, the CRISPR test is faster, more portable, uses different reagents, and can be immediately leveraged for two applications. The first is rapid, high-throughput screening of hundreds of respiratory swab samples at once, hopefully to alleviate the testing crisis in the United States and globally. The second is for use in point-of-care settings such as the emergency room, urgent care clinic, or even at home with the use of disposable cartridges and test strips.”
CRISPR-based systems have already been widely used by researchers to modify the genetic material in living cells. In the new test—called the SARS-CoV2 DETECTR assay—a system known as CRISPR-Cas12 is used to recognize the genetic signatures of the Covid-19 Coronavirus. If and when it finds the genes, the tool starts cutting, prompting a reaction which changes the color on a dipstick—in a process somewhat analogous to the way an over-the-counter pregnancy test works.
While the new test is slightly less sensitive than PCR-based tests, researchers claim this is unlikely to have much impact in diagnosis because infected Covid-19 patients typically have high viral loads. Charles Chiu said:
“In the short-term, I see the new test complimenting PCR tests, not replacing them. Each has strengths and weaknesses at present. We have completed validation of the test in a clinical laboratory, and are now submitting the test to the FDA for Emergency Use Authorization. The timeline for commercial and public availability for the test has been really sped up—less than a month for its use in clinical laboratories, and within three to four months for use in point-of-care settings.”
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