Everything you need to know about the different diagnostic tools for COVID-19, Dengue and Zika viruses


With the opening of several new laboratories performing these tests since the outbreak of the Covid, the cost and time of generating reports for the examinations have considerably decreased.

Representative image. PTI

Suggested to undergo RT-PCR testing but this time not for detection of COVID-19[female[feminine ? The outbreak of the pandemic familiarized Indians with this molecular test. But, to put it in perspective, the reverse transcription-polymerase chain reaction (RT-PCR) test is used to detect a variety of other diseases, including Zika and dengue.

With the opening of several new laboratories performing these tests since the outbreak of the Covid, the cost and time to generate reports for the examinations has decreased considerably. Experts estimate that in the pre-Covid era, only around 200 laboratories nationwide were performing RT-PCR testing. The number has now grown to 3,000.

News18.com talked to medical experts in order to understand what tests are used for the detection of COVID-19[female[feminine , Zika, dengue and chikungunya, and how they work.

RT-PCR tests

In molecular testing or RT-PCR technology, the virus is first extracted from blood samples or from nasal or pharyngeal swabs. The virus genome sequence is then allowed to multiply in an external environment (the body). This technology is considered a gold standard because it detects even a small amount of virus in the body, leading to early detection. Reports are generated within 2-4 hours.

During the first two to three days after the entry of the pathogen, for example a virus, their number would be too small to cause symptoms. Although these viruses or pathogens multiply every hour, it usually takes about 5-7 days for them to cause symptoms.

“So far the best technology for detecting most viruses is the RT-PCR test, also known as the molecular test. These tests are considered confirmatory in nature and typically generate reports within two to four hours. Although this test has been prescribed for several other diseases such as Zika, the price of this test and its availability have increased dramatically over the past year, ”said Dr Amrita Singh, head of laboratory services, Neuberg Diagnostics.

While the TrueNat and CBNAAT tests are also similar technologies, Singh said it takes up to 1.5 hours to generate results, but the machine can only load two samples at one time, while in RT-PCR, the machine processes 40 to 400 samples in a single run.

According to Dr Gautam Wankhede, director of medical affairs at Pune-based molecular diagnostics company Mylab Discovery Solutions, “as COVID-19[female[feminine is contagious and could prove fatal, its early detection is important. Therefore, RT-PCR is the preferable method to detect COVID-19[female[feminine . “

“For the detection of Zika virus, RT-PCR is a preferable method. Although the serological diagnosis of Zika is difficult, detection of nucleic acids by PCR is a suggested method. Even antibody tests do not give reliable results because they cross react with other viruses of the same family like dengue. Previously, there were cost constraints because the tests were expensive and few labs performed these tests. However, due to COVID-19[female[feminine , we now have over 3,000 labs in India doing these tests versus 200 labs in the pre-Covid days, ”Wankhede said.

According to the guidelines of the Ministry of Health and Family Welfare, RT PCR is also used for the early detection of chikungunya.

Rapid antigen test (RAT)

In the rapid antigen test (RAT), tissues in the human body are tested using an artificial or synthetic antibody.

“For example, COVID-19[female[feminine synthetic antibodies will be used on the COVID-19[female[feminine sample to see if a similar virus is present in the sample or not. However, this test requires a certain minimum number of viral particles to be positive, so there are chances to miss a few cases, ”said Wankhede.

According to government protocols for several diseases, including COVID-19[female[feminine , the negative RAT would force the patient to undergo RT-PCR while the positive RAT means positive. These tests are quick and give results in an hour, sometimes even 15 minutes.

In the detection of dengue, the ELISA method can be used. ELISA is an enzyme-linked immunosorbent assay, where this test detects antigen and antibodies in the blood sample.

“In dengue, the NS1 antigen ELISA is the preferred method by which the NS1 non-structural protein of dengue virus is detected. This protein is secreted into the blood during infection, ”Singh said.

Antibody tests

Any pathogen that enters the human body leads to the creation of antibodies. Detection of these antibodies in blood tests shows recent or past infection. However, these antibodies are not immediately generated by the body when the infection takes hold. Therefore, generally, these tests are not used for detection purposes.

In some diseases like COVID-19[female[feminine or dengue, where disease progression could prove fatal, antibody tests are of no value. Antibody tests are not popular or prescribed for diagnostic purposes but for surveillance purposes. It is counted as the last in the line for diagnostic purposes.

“These tests have taken a back seat and molecular tests have become more reliable and popular,” Wankhede said.

Antibody ELISA tests detect dengue and chikungunya but are not preferred for diagnosis because they show reliable results after 5-7 days of illness. These tests are only beneficial after confirmation of infection or receipt of vaccination.

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