What is FELUDA paper strip test for COVID19: Price, how it works, is it better than RT-PCR

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Touted to be more accurate, faster and cheaper than rapid antigen test for COVID19, India’s CRISPR ‘Feluda’ COVID-19 test is the new focal point as the number of cases increases at an alarming rate in India. The test that includes changing of colour on detection of the SARS-CoV-2 virus will be available by the first week of December. Union Health Minister Harsh Vardhan revealed that it is based on tests of over 2,000 patients during the trials at the IGIB and on testing in private labs which showed 96 per cent sensitivity and 98 per cent specificity. 

What is FELUDA test for COVID19?

The FNCAS9 Editor-Limited Uniform Detection Assay (FELUDA) test is a paper strip test, similar to a pregnancy test, and has been approved by the Drug Controller General of India for a commercial launch.

Named after the renowned detective created by Satyajit Ray, the test was developed by Tata CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) and the Council of Scientific and Industrial Research's (CSIR) Institute of Genomics and Integrative Biology (IGIB).

What is the price of FELUDA Covid test kit?

Developed by Dr Souvik Maiti and Dr Debojyoti Chakraborty at the CSIR-IGIB, FELUDA has been touted to provide results in 45 minutes and is priced Rs 500.

How is FELUDA test done?

1. Experts collect the nasopharyngeal swab. Then RNA is extracted
2. Then a single step RT-PCR is done.
3. FELUDA mix is prepared by incubating the dead FnCas9 protein, guide RNA and the amplified viral DNA. A dip stick is then immersed in the FELUDA mix.
4. Gold nanoparticle on the strip bind to the FELUDA complex. A protein called Streptavidin on the test line captures this gold nanoparticle bound-FELUDA complex. Unbound gold particles are captured on the control line
5. Change in color on the test line or control line shows the results
6. One line indicates negative, two lines indicate positive

Is FELUDA test better than RT- PCR?

FELUDA is an alternative to the quantitative RT-PCR tests and experts found it highly specific. As per the experts, it is capable of detecting low copy number nucleic acids (less viral RNA quantity) as well as single nucleotide variations. It can distinguish between SARS-CoV-2 and SARS-CoV sequences which differ by a single nucleotide.

While RT-PCR needs a few hours, trained manpower and a dedicated and expensive machine, FELUDA provides similar sensitivity and specificity but requires only a basic widely available PCR machine and no extensively trained manpower. Virologist Upasana Ray noted that the CRISPR based COVID-19 detection system is a cheaper option to RT-PCR tests, which cost over Rs 1,600.

How is FELUDA better than rapid antigen test?

Compared with a rapid antigen test, which interprets results in 30 minutes, Virologist Upasana Ray said the Feluda test would take slightly longer, up to 45 minutes, but is more accurate and specific. Rapid antigen tests detect the viral proteins or parts thereof whereas CRISPR detects nucleic acids, or RNA in case of COVID-19, Ray said.