Roping in ‘Feluda’ to detect Covid-19

As India’s Covid-19 positive cases cross the 5,000-mark, with evidence of community transmission in some cities, there is pressure on India to increase testing to slow the spread of infection. Since the country’s first case was reported in January, it has been using the same testing mechanism that most countries around the world are using — the reverse-transcription polymerase chain reaction or RT-PCR test. According to the Indian Council of Medical Research, the 135 government and 56 private laboratories with RT-PCR machines can together do only 18,000 tests per day. Given this shortfall, a seven-member team of scientists and researchers at CSIR-IGIB (Council of Scientific and Industrial Research’s Institute of Genomics and Integrative Biology), New Delhi, led by Dr Souvik Maiti and Dr Debojyoti Chakraborty, has developed a new low-cost paper strip test that is expected to get regulatory approval by the end of the month.

In an interview to BL ink , Maiti and Chakraborty explain how the test — called Feluda — could be a game changer in India’s efforts to swiftly curb the pandemic.

How does the paper-strip test detect Covid-19 infection?

Maiti: Through a nasal swab, we get RNA samples of the virus from the patient.

We first convert this RNA into genetic material or complimentary DNA (cDNA). Then we amplify it using a polymerase chain reaction (done on a simple PCR machine) and mix with a complex Cas9 protein. The Cas9 protein specifically binds to the DNA signature of the Covid-19 virus. Finally, this mixture is applied on a paper strip. Depending on the presence of Covid-19 DNA, a line appears on the paper strip, apart from a control line that appears regardless of whether the virus is present or not.

Chakraborty: If there is presence of even low amounts of viral RNA, it will detect it. The results are known within 1.5 hours. When we scale production of the testing kits, it could be even faster. This is a qualitative test, so it can tell you presence or absence rapidly, but if you want more quantitative data then you can always do that with a more sensitive RT-PCR technique.

What kind of effort went into putting together such a kit?

Chakraborty: We had been working on a pan-detection test from much earlier... to detect any DNA and RNA, bacterial and viral infections, and genetic mutations causing diseases. In end-January we optimised our test to detect the Covid-19 RNA. By March we began testing it on patient samples with accurate results.

We decided to tackle it head on... even through the lockdown. Students volunteered and several stayed back on campus to work on this day and night.

What will be the cost of this test, and how accurate is it?

Maiti: We are estimating the cost to be ₹500-700.

The specificity of the test is 100 per cent, which means that all positive samples are reported as positive. The selectivity is 90 per cent, which means if we get 10 samples that are negative, the test would reveal only one of those to be falsely positive.

At this moment we are still testing our kit on patient samples. Simultaneously, we are approaching third-party validations, after which we’ll aim to have regulatory approval by the month end. After approval we can partner with companies to scale it up.

How does it compare with the RT-PCR test and others such as the Mylabs kit developed in Pune that has got regulatory approval?

Maiti: The starting material is the same in RT-PCR and our technology. Both need RNA samples. The RT-PCR method demands highly specialised RT-PCR machines, which are mostly imported and cost ₹25 lakh... only specialised hospitals have it. You also need trained manpower to run it. It has to go through some mathematical calculation before you decide whether the sample is positive or negative.

Our kits use simple PCR machines, which are mostly produced in India and cost around ₹2 lakh. For every RT-PCR machine there are roughly 100 PCR machines, which are also available in tier 2 and 3 cities. Also our testing can be done by the average BSc graduates familiar with compounds and calculating sample concentrations. A simple seven-day training would be enough to impart skills needed to conduct these tests. This helps to localise the tests in low-resource areas.

RT-PCR diagnostic machines can run a maximum of 96 samples in a four-hour window. Our process takes a fourth of that time.

RT-PCR will show quantitative accuracy, but the paper-strip test will be helpful when we start seeing thousands of patients lining up.

And, finally, while the RT-PCR method costs ₹4,500, ours will be under ₹700.

Why did you name the test ‘Feluda’?

Chakraborty: The reason we named it ‘Feluda’ was because a competitive paper-strip test being developed by MIT and Harvard goes by the name ‘Sherlock’, after the famous [fictional] detective. So we wanted to give it an Indian twist and decided to call it ‘Feluda’, after Bengal’s most famous detective character created by Satyajit Ray. Also ‘Feluda’ is an acronym for the scientific name of the test — Fncas9 Editor Linked Uniform Detection Assay.

Will cheaper and more rapid testing be the real game changer in the country’s Covid-19 battle?

Maiti: Right now there is no paper-strip test diagnostics across the world. Even South Korea had used the expensive RT-PCR method to flatten its curve. We are really hopeful that it will work. We haven’t failed a single time in detecting a positive sample so far. We are in talks with several corporate houses such as Reliance and Tata Sons, which are forthcoming about backing us to scale this. We have also filed two patents.

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