Around three months have passed since the city of Wuhan in China was put under lockdown. Since then, Covid-19 has swept the globe, with over two million people infected.
Public health officials worldwide are faced with mounting challenges to gain the upper hand on the virus. A major concern is: how to find people who are infected with the virus but do not display any symptoms – known as asymptomatic carriers? Swiftly identifying such cases will enable timely interventions such as isolation and quarantines to halt further spread of the novel coronavirus – referred to as SARS-CoV-2.
A team of scientists from the University of Cranfield, United Kingdom, is working on a low-cost, paper-based device that can detect SARS-CoV-2 in the wastewater of communities. The cost per device is less than Rs 96 and a positive result is easily visible as a green circle in about 30 minutes after adding the sample.
“This test will be able to detect whether there are potential Covid-19 carriers in local areas without any known cases,” said Zhugen Yang, a lecturer in sensor technology at Cranfield Water Science Institute. It is also possible to determine how much virus is present by capturing and analysing images, he added. The team has tested the device with the genetic material of the virus in wastewater for proof-of-concept and it shows “high potential to detect SARS-CoV-2.”
In India, almost 16,400 active cases of Covid-19 have been logged as of April 23. And more than 100 cases have been recorded in Dharavi, Mumbai’s cramped slum, housing more than half a million.
After growing calls to ramp up testing, India aims to reach a testing capacity of up to 100,000 per day, according to a report. But with its vast population and limited resources, widespread testing is a massive undertaking and remains a tall order logistically.
Consequently, researchers are developing a rapid, on-site test using a wastewater epidemiology approach where wastewater at treatment plants can be tested as an early monitoring tool to help local governments and agencies to decide effective courses of action.
A subgroup of Covid-19 patients with the mild disease first developed gastrointestinal symptoms such as diarrhea before respiratory symptoms and these patients were more likely to test positive for the genetic material of SARS-CoV-2 in their faeces, according to a study of patients in Wuhan published in March in The American Journal of Gastroenterology.
Since infected individuals can excrete the genetic material of the virus in faeces, research groups around the world are testing sewage as an environmental surveillance mechanism. Traces of the virus have been found in wastewater in the United States, Netherlands and Sweden.
How it works
Typically, the genetic material of SARS-CoV-2, RNA, is detected in a laboratory through an assay called Reverse Transcription-Polymerase Chain Reaction or RT-PCR. This method converts viral RNA to DNA, the latter of which is amplified. While PCR is highly sensitive, it has some requirements that make it difficult to conduct, especially in developing countries, the researchers say.
For example, this test requires an equipped laboratory with skilled personnel who can handle the samples. Moreover, the results are available only after a period of four to six hours.
The paper-based device is folded and unfolded to filter the nucleic acids of the virus from wastewater, which then reacts with preloaded reagents that reveal the presence of SARS-CoV-2. A green circle indicates a positive result. With further modifications, Yang said, the device will be easy to use by non-experts.
One major advantage of the device is that no power is needed, which would make it suitable for regions where power supply is unreliable. Apart from this, “paper analytical devices are also easy to stack, store and transport because they are thin and lightweight, and can also be incinerated after use, reducing the risk of further contamination,” Yang added.
“This technology has the greatest potential for use in the developing world, where expensive equipment and means for sample and reagent refrigeration are limited or absent,” said Rolf Halden, professor of health engineering at Arizona State University and author of the 2020 book, Environment. He is not involved in the development of the paper-based test.
With funding, the team is currently improving the performance of the device. “We have been approached by a water company for discussion on collaboration,” added Yang. In an earlier initiative, Yang and his colleagues had developed a similar paper-based device for detecting malaria in blood samples of rural populations in Uganda.
Punyasloke Bhadury, professor of biological sciences at the Indian Institute of Science and Research, Kolkata, said that because “mortality from SARS-CoV-2 is ascending along with new reports of infection on a daily basis, tests, including the paper-based device may help identify suspected and asymptomatic infected cases in countries which lack robust testing laboratories.”
However, “the long-term success of the paper-based device can only be confirmed when evaluated across a large number of samples with geographic coverage,” he added. “Overall, all available means of testing should be deployed in this challenging time globally, including in India.”
The test’s accuracy
Yang said that the testing kits involve a technique called isothermal amplification, which enables a similar sensitivity as PCR. Like PCR, isothermal amplification involves a “biochemical reaction to enrich nucleic acid with the enzyme as a catalyst, so they both have a high efficient signal enhancement for detection of viral RNA and similar performance in terms of sensitivity,” explained Yang. “PCR needs a thermal cycle limiting it in the lab, but isothermal amplification can happen at a constant temperature, therefore without the need of power and can be performed on-site.”
But experts said that paper-based assays tend to be less sensitive and specific than PCR and will still require validation. Although “these assays are much less expensive,” they “tend to lag behind in sensitivity, selectivity and accuracy when compared to gold-standard methods,” cautioned Halden.
“Wastewater is a challenging diagnostic matrix due to its complex chemistry and microbiology,” Halden said. “Paper-based assays, once developed for SARS-CoV-2, likely will perform better in healthcare settings. Wastewater is a touchstone diagnostic matrix and more often than not, it gives us analytical chemists a serious headache,” he noted.
Rosina Girones, professor of microbiology at the University of Barcelona, said the paper-based technology is promising and may be very useful in the future, but she also echoes Halden’s concerns. “We need to know if the sensitivity of the assay is enough to detect few viruses in about one millilitre of a sewage sample,” she said, pointing out that “this is a limiting parameter in environmental studies, and also the specificity in terms of viral strains detected.”
Girones added that we still “need to develop the specific assay for SARS-CoV-2, an RNA virus requiring reverse transcription, and also optimise the sensitivity of the assay and the volume of the sample tested to be sure that it is enough sensitive and robust to obtain reliable information.”
This article first appeared on Mongabay.