[ed. note: Michael Jorrin is a longtime medical writer (not a doctor), I’ve dubbed him “Doc Gumshoe” for his coverage of medical and health topics for Stock Gumshoe. This piece, like most of Michael’s work, is not specifically investment-related — but for those who think about speculating in the next Zika cure or similar “hot tip” a little background might help]
Last year Ebola was terrifying parts of Africa, with reason, and making lots of us on this side of the Atlantic distinctly uneasy – with, in my view, much less reason. Now the scary virus is Zika, which really is a frightening reality in large parts of Latin America, as well as parts of Africa and Asia, but much less menacing in the US and Canada, and much less in Europe as well. And now we have to worry, at least a little, about MERS (Middle East respiratory syndrome), as well as an assortment of flu viruses. As for the human immunodeficiency virus (HIV), fortunately, in the developed world, it can be controlled reasonably well in most patients. Unfortunately, there are large parts of the world where it continues to rage out of control.
Do we have the impression that new viruses are emerging with increasing frequency, causing more devastation? Well, that’s only if we abandon historical perspective. The influenza pandemic, which started in January of 1918 and lasted nearly three years, infected 500 million people and killed at least 50 million and perhaps as many as 100 million – about 5% of the global population at that time. It was the most deadly epidemic since the bubonic plague in the mid 14th century.
But it does seem to be the case that viral diseases travel more quickly and easily from the location of their initial outbreak to distant parts of the planet. The virus can’t really go anywhere on its own, but the host – the person or animal infected with the virus – can go halfway around the globe in a few hours and transmit the virus to another host. And, because viruses mutate, there is always the fear that a virus which had been previously thought to be a factor only in certain regions might thrive and become a threat in our own vicinity. This fear is not paranoid, but it needs to be tempered by a bit of information about viruses, their carriers, and their hosts.
So, forgive me if you already knew this, but it probably wouldn’t hurt to review what we know about viruses.
What are viruses, and how do they make us sick?
Virus is a Latin word meaning, essentially, a nasty, slimy, evil-smelling, poisonous liquid. The name was first used at the end of the 19th century to describe infectious agents that could not be seen by an optical microscope or trapped in a filter designed to capture bacteria; thus the Latin term seemed to be entirely appropriate. For several decades after it was determined that there were such infectious agents, the term “filterable virus” was frequently applied to them. Pasteur and other 19th century scientists had reasonably good evidence that such agents really did have the capacity to cause infections. No microbe detectable with a microscope seemed to be the cause of rabies, but rabies was clearly transmitted by the bite of an infected animal. The tobacco mosaic spread from plant to plant, yet no agent was visible, nor could any agent be trapped by the filters that caught bacteria.
However, scientists suspected early on that viruses were something more than “liquid life,” as they were sometimes described. In 1915, the following statement appeared in Lancet: “We do not know for certain the nature of an ultra-microscopic virus. It may be a minute bacterium that will only grow on living material, or it may be a tiny amœba which thrives on living micro-organisms. It is quite possible that an ultra-microscopic virus belongs somewhere in this vast field of life more lowly organised than the bacterium or amœba.”
The speculation that a virus was “a minute bacterium” was borne out about 20 years later, when, with the development of the electron microscope, it became possible actually to see that viruses were discrete individual particles and not a liquid life form. It was just that they were so much smaller than the smallest previously observed micro-organisms that they could not be seen through optical microscopes. As to what they actually were, the investigation was just beginning, and would not really produce significant results until the second part of the 20th century.
How much smaller than bacteria are viruses? Their size is calculated in nanometers (nm), generally between about 20 nm and 300 nm, whereas bacterial size is calculated in micrometers (μm). A nanometer is a billionth of a meter, while a micrometer is a millionth of a meter – a thousand times larger. So, in general we can say that bacteria are a few hundred to a thousand times bigger than viruses.
Viruses are not cells. They are composed of two or at most three parts – a core consisting of RNA or DNA, a capsid or capsule around that core, consisting of proteins, and in some viruses, a coating or envelope consisting of a simple lipid. Viruses depend for their existence and function on host cells, whether the cells are in animals or in plants. Once they enter the host cells, they are able to reproduce.
While cells of any kind, human or otherwise, reproduce by cell division, viruses copy their genetic material inside the host cell. Once they attach to a host cell, they penetrate the cell wall, move inside, shed their outer layers, and kidnap the host cell’s resources to copy their RNA or DNA. The newly-formed virus cores then construct protein capsids around the cores. If it is a lipid envelope virus, it also forms that part of its anatomy, all of this stealing the host cell’s resources. This process usually kills the host cell. The virus then emerges into the intracellular space, attaches itself to another host cell, and continues the process of reproduction.
Whether viruses are alive or not is a matter of some dispute, although from my point of view that dispute should be left to philosophers and theologians. It seems clear to me that viruses are indeed alive. Why else would they go through all the steps described in the paragraph above if not to be fruitful and multiply? Sounds like life to me.
But viruses need transportation to get to the hosts
Viruses are hitchhikers. They have no means of locomotion. But they do manage to get from one host to another with great success. For example, if you have a cold, when you cough or sneeze, you are propelling a huge number of virions (that’s the name for an individual virus particle) into the air in your immediate proximity. If someone is in the space into which you discharged your viral explosion, that person may inhale some of those virions and become infected. In any case, a portion of that viral load will settle on a surface somewhere – a surface that someone else may touch. Then that person has virus on his or her hands,