You are currently browsing the tag archive for the ‘PCR’ tag.

Infected? Or Infectious? The HUGE Difference!

By Shlomo Maital

There is a basic problem with COVID-19 testing. And it’s NOT the number of tests alone. It’s the kind of test. It rests on a simple distinction between ‘infectious’ and ‘infected’.

   Current tests that are FDA approved use PCR – polymerase chain reaction [ a method to rapidly make millions to billions of copies of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it to a large enough amount to study in detail. For COVID-19 tests, PCR multiples the RNA comprising the virus, if there is any, so it can be detected by a rather complex machine and its operator.] The PCR tests test for the presence of coronavirus and the results often take a long time to produce. THESE TESTS ONLY DETERMINE IF THE PERSON IS INFECTED. But they may notv be INFECTIOUS. Why? Because the viral load in their bodies may be so small, that they are really not likely to spread it. PCR tests cannot tell the difference between infectious and infected.

     New tests are on the way. They CAN test if the person has such a high load of virus, that he or she is INFECTIOUS.   These tests, developed among others by epidemiologists at Yale University, can be done at home, using a saliva test not unlike a pregnancy test. They do measure viral load, and signal whether the person is infectious.

     This is what we need. A cheap $1 test, done at home, mass produced, done daily, so each of us can tell whether we have the virus AND ARE LIKELY TO SPREAD IT TO OTHERS IF WE LEAVE OUR HOME OR POSSIBLY EVEN INFECT OTHERS AT HOME.   These tests need to be done daily.

     This distinction was explained on an excellent podcast, Ira Flatow’s Science Friday.

       Why haven’t we gotten such tests sooner? Money. These tests are developed mainly by startups and small labs. They lack the resources to accelerate development and then scale them up. And governments, like the US government, have put billions into vaccines…Operation Warp Speed – and virtually nothing into developing the kind of tests that are needed. The US Admiral who heads Operation Warp Speed keeps telling the media that “we are doing everything possible” – but he is not, and the government is not.

   Infectious? Or just Infected. Help spread the word that the difference is hugely important!

p.s. CIDD is the Center for Infectious Disease Dynamics, at Penn State Univ.

How an Overnight COVID-19 Test Took 35 Years to Invent

By Shlomo Maital

Dr. Fang  Zhang

   As Darwin observed, when he was praised for his breakthrough: Scientists stand on the shoulders of giants. Now, a new genetic test for COVID-19 may be as quick, simple and cheap as a self-administered pregnancy test, with two lines on a slip of paper.

     Here is the story. Let’s begin by noting that the hero is ethnic Chinese, Fang Zhang, a researcher at MIT’s Broad Institute. With massive anti-Asian and anti-Semitic hatred filling the Internet, it is fitting the hero should be named Zheng.

     Chapter One. Some 35 years ago, a biologist named Kary Mullis invented PCR. Polymerase chain reaction (PCR) is a method used in molecular biology to rapidly make millions to billions of copies of a specific DNA sample. This allows scientists to take a very small sample of DNA and amplify it to a large enough amount to study in detail. For example, suppose you are looking for the presence of the genetic material of a virus. You take a swab, use PCR, make millions of copies of the stuff, and then it becomes easy to detect it in a test tube.   Mullis won the Nobel Prize for this discovery, in 1993.

     Chapter Two. CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats. (A palindrome is a word or phrase that reads the same forwards and backwards, e.g. a man a plan acanal panama. ) The discovery of clustered DNA repeats occurred independently in three parts of the world. The first description of what would later be called CRISPR is from Osaka University researcher Yoshizumi Ishino and his colleagues in 1987.

     Say you want to modify a specific gene – snip it out, replace it, test it, etc. First, you ‘tag’ it with a molecule (like putting a big road sign, “HERE I AM!”, on it). Second, you attach an enzyme to the tag. The enzyme cuts the CAN right at that spot!   You can then replace the faulty or offending gene with a different improved one.

     Chapter Three. MIT. Dr. Zhang and other researchers have retooled CRISP-R. They use it not to snip out a gene, but to give a signal that the enzyme has reached its target – a piece of genetic material that is unique to COVID-19. When this happens, a screaming signal is emitted, say, figuratively, a bright Day-Glo sign saying, Yikes, it’s the novel coronavirus!  

       Chapter Four. Translate the complex lab procedure to a simple cheap test. Take samples from a person’s throat and nose. Put it into a test tube with chemicals that tear open viruses.   Use an eye dropper to put some of the liquid into a second test tube containing CRISPR. Put the test tube in hot water, at 140 degrees F. (80 C.). Stick a piece of paper into the tube. If two lines appear: COVID-19 is present.

     The test worked on 12 patients, and can be simplified greatly and produced at $6 per test. This may enable massive population-wide testing, that can help open societies and economies without a massive second-wave of plague.

       Classic scientific breakthrough: 35 years, and an overnight breakthrough!




Blog entries written by Prof. Shlomo Maital

Shlomo Maital