Coronavirus Detection

The number of COVID-19 cases has been increasing across the world. Countries are racing to test larger portions of its population.

Steps Involved in Testing

There are 5 steps involved in testing a sample for the virus:

• Collection: the sample is collected from the throat and nasal cavity. It is stored in a medium composed of albumin and salts to preserve the virus and transported under cold conditions.
• RNA extraction: the RNA of the virus is extracted (SARS CoV 2 is a single stranded RNA virus).
• Treatment with PCR Mix: this converts the RNA into DNA and creates copies.
• DNA amplification: the genes in the DNA are amplified with the help of a thermal cycler machine. It runs 30 to 40 cycles.
• Testing against controls: the amplified DNA is tested against controls to determine whether the sample is positive/ negative for the virus.

PCR Mix

The PCR (Polymerase Chain Reaction) Mix consists of the following:

• Master mix- made of reverse transcriptase enzyme (to convert RNA into DNA), Taq polymerase enzyme (to create DNA copies), nucleotides, magnesium ions (to amplify the DNA), etc.
• Reagents- like primers (DNA strands designed to bind with the DNA meant to be copied) and probes (to detect specific DNA sequences).
• Housekeeping gene- a human gene, RNase P, used to make sure that the samples were collected and the RNA was extracted properly.

Positive/ Negative

The samples are tested against 2 types of controls:

• Positive control is the genes of the virus cloned into plasmids. The test should yield a positive for this control.
• Negative control is a known sample that had previously tested negative for the virus. This should give a negative result.

When these two conditions are met, the sample is determined as bearing the virus or devoid of it depending on whether it gives a positive or negative in the test.