Decoding Feluda: The test that detects Covid-19 quickly, cheaply and easily

This test uses an indigenously developed CRISPR technology for detection of the genomic sequence of SARS-CoV-2 virus.
The Drugs Controller General of India (DCGI) approved the commercial launch of ‘Feluda’, the Tata CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) Covid-19 test on Saturday. The new test - Feluda, named after the fictional detective character created by renowned filmmaker and writer Satyajit Ray is said to be easy to use, provides faster results and at a much lower cost than existing Covid tests such as the RT-PCR. We try to find out how this test works and what it means for India’s testing capacity.  

What is the technology behind this test?

This test uses an indigenously developed CRISPR technology for detection of the genomic sequence of SARS-CoV-2 virus. It has been developed by the Tata group and the Council of Scientific and Industrial Research (CSIR) using the gene editing technology that identifies the DNA sequence of SARS-Cov2. Feluda is the acronym for FNCAS9 Editor-Linked Uniform Detection Assay.

It is a paper strip test where the Cas9 protein, a component of the CRISPR system interacts with the Sars-CoV2 sequence in the patient’s genetic material. Two lines on the strip then decode the result of whether one is infected. If a person has the genetic material of the virus in its sample then the CRISPR enzyme would glow. The genetic material of a patient can be sampled via a nose, mouth or throat swab, or in fluid from the lungs.

CSIR claims the test gives a result in less than an hour and is as accurate as the real-time polymerase chain reaction test (RT-PCR) test which is considered the gold standard for Covid testing.  Unlike the RT-PCR test, Feluda does not require a lab-set up and achieves accuracy levels of traditional RT-PCR tests, with quicker turnaround time, less expensive equipment, and better ease of use, according to a Tata group statement.

The test according to a Tata group statement meets the ICMR guidelines for meeting high quality benchmarks with 96% sensitivity and 98% specificity for detecting the novel coronavirus. Tata group also said that CRISPR is a futuristic technology that can also be configured for detection of multiple other pathogens in the future.

How much does it cost and how does it compare to other tests?

Feluda test costs Rs 500 which is much less compared to the price of an RT-PCR test that can range from Rs 1,600 to 2,400. The latter gives results in 24 hours and sometimes takes days due to the requirement of a lab-set up and skilled manpower. The antibody test costs around Rs 600 and results can be known in half an hour but it is not meant for diagnostic purposes. The Rapid antigen test which is now being used by many states to detect Covid-19 costs less than Rs 500 and takes 30 minutes for a result but is not as accurate as the RT-PCR.

The other tests approved by the ICMR such as the cartridge- based nucleic acid amplification test (CBNAAT) or the TruNat test can cost more than the RT-PCR but provide faster results.

What does the new test mean for India’s testing capacity and fight against Covid?

India has ramped up its capacity to 1 million tests per day. However, the network of testing labs is poor in smaller districts and non-existent in the rural belts. Test samples have to be couriered to labs in nearby cities. A low cost test that can be made easily available will help in faster detection of cases and therefore improve the reaction-time. Girish Krishnamurthy, CEO, TATA Medical and Diagnostics Ltd, said, “The approval for the Tata CRISPR test for Covid-19 will give a boost to the country’s efforts in fighting the global pandemic.”

Do other countries use a CRISPR-based test for detecting Covid-19?

World’s first coronavirus test using the gene-editing CRISPR technology was developed by the Massachusetts Institute of Technology and Harvard University in May. The United States drug regulator had granted emergency use approval to the test.


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