The Horseshoe bat is now infamous as the source of the virus which has caused the tragic covid 19 pandemic. It is well documented by genetic studies that these bats were the reservoir for the virus. Thus it may be of interest to know something about these critters—and how they evolved to infect others of the same species—which have in some way brought down the wrath of Mother Nature on a world society which was intent on thumbing its nose at Mother Nature.
These bats are part of a group of “microbats”—belonging to the genus Rhinolophus (meaning “crested nose”.) This critter is a native of China, Asia, Africa and Europe. Horses bats are small—about the size of a humming bird- with a wingspan of only six inches. They weigh almost twice as much as hummingbirds at about one ounce (@ 28 grams). The wings are broader and shorter than other bats, making them well adapted to the cluttered, tight spaced environments where they hunt for insects and spiders among vegetation. They use the near continuous sound generated by an organ.within their nose for echolocation . The reception of the echoes is enhanced by the unusual horseshoe shaped nose flaps which give them their common name: ‘horseshoe bat”. They hunt for insects and arachnids which they take in the air or swoop down on from a perch. Like most bats they fly at night and during the day roost in caves, tree hollows and buildings. Those that hibernate favor caves with temperatures of about 50 degrees F ( @10 C)
How did these tiny bats become a source of a human virus? The answer is that even though very small (unbelievably) they are used as a source of food as well as the basis of several home medicine concoctions by several groups of people in Asia and parts of Africa. In addition, the bat guano of this family is often collected—from caves—for use in cosmetics and medicines in China and elsewhere in the Old World. These activities no doubt brought the bats and their virus carrying body fluids into contact with humans.
We know that this group the Horseshoe bat (especially a species known as the Chinese Rufous Horsehoe Bat) is a source for several species of coronaviruses and in particular the Covid19 virus which has caused the 2019 pandemic. At the time of this writing Covid 19 has caused nearly 3 million cases of flu worldwide and well over 200,000 death. In the USA, there have been over a million cases and over 50,000 deaths to date. The social chaos both medical and economic has been tragic.
It is uncertain how the Covid 19 virus passed from one or more species of Horseshoe bats to infect humans. Some claim that the bat virus may have first infected other animals ( a wild feline known as the Palm Civet, or the an unusual scaly wild mammal—the Pangolin). The bats as well as the other wild animals possibly infected by bats have been used as food, or “medicines”in China and in that way, either by handling the animals, keeping them in cages and living or working in close proximity to the caged animals before they were killed for consumption, or during transportation, or for other purposes —the virus was transmitted to humans—in or near Wuhan China. Once humans were infected in China —the virus—finding suitable conditions for reproduction—rapidly infected others and spread world wide.
But what we do know with certainty is the the Covid19 virus evolved in bats. This fact has been confirmed by numerous genetic studies of the virus’ RNA/DNA. We can assume that the process of Darwinian evolution and adaptation to its environment and the survival of the most efficient forms resulted in a viral entity that was most effectively adapted to pass its genetic material from one bat host to another— most likely in the crowded roosting caves.
Bats—like humans—do not live solitary lives. They forage at night singly—in flight —catching insects on the wing or swooping down on insects or spiders on leaves or branches. During the day they congregate in congested communal roosts in caves, buildings or hollow trees. That is where this virus evolved: in congested. enclosed places with still relatively dry air.
It was in these enclosed confined environments that the virus must have evolved to infect its bat hosts by efficiently passing from one bat to another by means of respiratory transmission in the confined spaces. Transmission by aerosols in these places is a most effective means of infection.
As the bats roosted—in close proximity to others—their exhalations produced droplets of saliva that would be lofted into the still air. These could be then inhaled by other bats roosting near-by. Under the right conditions of cave temperature and humidity these droplets could slowly evaporate, loosing moisture to the surrounding air by evaporation, making the droplets smaller and lighter, (and thus more likely to remain lofted longer). This would increase their chance of being inhaled by other more distant bats and would be selected for . Over time evolution likely favored those viruses which might survive being subjected to low humidity, (drying conditions) that would leave the virus suspended in the air with little or no moisture —or with only the minuscule viral particle which could remain in even still air for very long periods of time. Such an evolutionary course would make it many times more effective in transmission to other bat hosts even further away in the roost and would favor those characteristics over others.
Such evolutionary adaptations in the Horseshoe bat virus made it particularly well adapted— perhaps we can say “preadapted”—for efficiently infecting other hosts with similar life ways: i.e. living in crowded enclosed spaces in close proximity to others.
We humans live like bats!
In some circumstances we live like bats. Regularly crowding ourselves into small congested rooms in close proximity to others, in airplane fuselages, closed classrooms, crowded tenements, and subway cars where humans are exhaling aerosols which can then be inhaled by others near-by. This is an ideal circumstance for the virus which evolved in the Horseshoe bats.
The coronovirus covid 19 when it became a zoonosis (a disease which can be transmitted from animals to human). Upon entering human hosts it grew in population very much like an invasive species. It found a “new environment” with no existing controls on its expansion and a practically unlimited supply of hosts.almost 7 billion of them. It’s population soared just like any other alien invasive species. (The infamous Cottontail Rabbit plague of Australia is a particularly interesting case. In 1788 colonists introduced 24 English cottontail into Victoria, Australia and within 30 years the entire continent was overrun with rabbits. Recurrent “rabbit plagues” have continued in Australia up to modern times. At its peak in 1910 there were estimated 10 billion rabbits in Australia. Today after many decades of extermination and introduction of specific rabbit diseases the rabbit population is estimated there are at a mere 200 million.)
So knowing this we can perhaps better understand how to control the transmission of the virus in humans. Aware that this virus has evolved to transmit its genetic material by means of aerosols which enter the air and may remain lofted for long periods of time—the loft time being dependent upon temperature, humidity, solar radiation, and air flow patterns—then while floating in the air may be inhaled by other hosts. Just like in the bat cave.
Thus we must avoid enclosed crowded places —virtual bat caves—where potential carriers may have introduced the virus into the air we breathe. Enclosed places where aerosols produced by carrier-hosts can remain lofted in the air and thus become possible vectors of disease. Since at this time we are not certain who is a carrier and who is not, we must assume that everyone is a possible carrier.
It is clear that our habits and proclivities to maximize the profits of a few by jamming as many people as we can into tight seats on airplanes, crowded sports stadia, bulging classrooms, over crowded restaurants, massive music festivals, and the abomination of disgusting cruise ships which carry huge crowds confined in tight quarters where germs are so efficiently dispersed then debouching these disease racked individuals at ports of —“tourist cities” around the world to spread disease and pandemics . All this will have to end—if we want to survive as a nation.
Let’s be clear. There is no possibility of eliminating the threat caused by OUR dangerous habits of crowding—even if we find a cure and a vaccine for covid-19–there are hundreds of others similar viruses out there lurking and evolving in the biosphere-that will take advantage of a society which attempts to thumb its nose at Mother Nature. A society which foolishly ignores the biological imperatives of the natural world—to avoid crowds—and still survive.
Our lives will have to change drastically if we are to survive this biological threat. For now it is imperative that we wear masks to substantially reduce the release of aerosols our that may carry the virus and infect others. Even if we think we are not sick—the disease has a long period of asymptomatic early stages which give us no warning of infection. We do not know if we are sick. In addition there are many cases of of only minor symptoms or asymptomatic carriers.
We must all avoid crowded locations where body fluids may be aerosolized to float in the air that we breathe and where they can remain under some circumstances for very long periods of time.
We must also be aware of the other means of transmission by viruses which may survive on surfaces which are touched by others. Wearing gloves does not mean that your hands are sterile. That sterility lasts only a short time after you have removed the gloves from the box.
We thumb our nose at Mother Nature at our own peril.
No comments:
Post a Comment