17.6 C
Thursday, October 6, 2022
Dr. Brown: How the coronavirus attacks

Dr. William Brown
Special to The Lake Report

Unlike simple cells such as bacteria, viruses like the corona family of viruses, travel light: without help they can’t make their own RNA, proteins or generate energy. That means they need a host, and in this pandemic, we’re it.

They target the cells lining our respiratory tract from the nasopharynx (sneezing), to the trachea and bronchial tubes (coughing) and, especially, the far reaches of the respiratory system, the alveoli where gas exchange takes place (shortness of breath). Even simple breathing scatters clouds of tiny droplets that can hang in the air for hours.

But how does the virus get into our cells and make copies of itself before killing the host cell? This is important because this is where strategies begin for inhibiting or killing the virus before it gets into our cells. Let’s start with normal cells before looking at how this virus highjacks them.

To make proteins, cells evolved a marvellous system. First, the information in the cell’s nucleus, which specifies the number and sequence for the amino-acid building blocks for a given protein, is copied from the related gene in the DNA to a single-stranded molecule called messenger RNA (mRNA).

The latter then moves to the cytoplasm of the cell where the mRNA’s code is read by structures called ribosomes to create a gene-specific protein whose function critically depends on the amino acid sequence and the 3-D shape of the protein. It’s a neat system, whose molecular biology was worked out many years ago. Now it gets interesting.

The coronavirus’s RNA, once inside the cell, usurps the cell’s natural mRNA and highjacks the cell’s normal system for creating proteins, to create its own molecular building blocks. The latter include the proteinaceous spikes (the corona) sticking out from the surface of the virus, the glycoprotein shell, which normally protects the virus’s RNA and, of course, copies of the virus’s RNA. After that those parts are assembled into hundreds, if not thousands, of copies of the virus before finally the cell bursts, releasing the horde of copies into the body.

The viral progeny goes on to repeat the process many times over, and in their wake, create widespread destruction of the targeted cells and an inflammatory response, which may be as life-threatening as the viral invasion. But how does the virus get into the cell? Here’s where treatment comes in.

Each cell in the body has specific molecular identifiers on its surface that act like gates to control access to the vital interior of the cell. The COVID-19 virus’s spikes express molecules on their surface which can reach out, latch onto and open those gates. From that point the virus is free to wreak havoc by taking over the cell’s operating systems and cranking out copies of itself. Those same spikes are also armed with other molecules that may mask the virus from the body’s immune system – a double hit!

Developing effective anti-viral agents is a matter of identifying those specific molecules on the virus’s corona of spikes, responsible for the virus gaining access to the cell’s contents and masking the virus from the immune system. Several companies are working on developing such bioengineered antiviral agents but so far, they’re in the pipeline and not ready for prime time. Don’t look for much help here for at least six months, although with luck, success may come earlier.

Then there’s the matter of vaccination. It wasn’t very helpful against SARS, a close relative of COVID-19 and we may not know for many months whether an effective vaccine can be mounted against COVID-19. Hence the importance of walling off the virus by separating the vulnerable – the yet uninfected, especially those at high risk – from those carrying the virus.

The latter is tricky because without widespread and timely nose/throat RNA testing, for which this and many other countries, are woefully unprepared, it’s hard to prevent the spread of the virus. Social distancing (six feet or more) and hygiene (cleaning surfaces and hands regularly) are, of course, public health staples and may slow the spread of the disease.

The downsides are predictable. Social distancing is hard to enforce without draconian measures (China) and demoralizing if carried out too long as we are, after all, a highly social species. It also destroys economies and jobs on which communities and nations depend. Tough days are ahead even  though hope is on the horizon!.

Dr. William Brown is a professor of neurology at McMaster University and co-founder of the Infohealth series held on the second Wednesday of each month at the Niagara-on-the-Lake Public Library.