Brief navigating note: I've added a new category tag for all posts in this ongoing series about diseases that are supposedly transmitted via encounters, but which are in fact transmitted via a contaminated shared medium. It's "Neo-Anticontagionism" -- "contagion" referring to contact and touching, i.e. close encounters, as the way diseases are spread. It appears at the end of every post in the series, as well as in the sidebar on the right called "Category Index". I don't know how long the series will be, but it's important and distinctive enough to put it all in one convenient place.
This post will look at the two most famous coronaviruses aside from SARS-CoV-2, which also cause acute and severe respiratory symptoms in human beings, namely SARS-CoV-1 (causing the Sudden Acute Respiratory Syndrome outbreak of the 2000s), and MERS-CoV (causing the Middle East Respiratory Syndrome outbreak of the 2010s).
I'm sure the broad lessons about transmission from these three well-studied cases will generalize to other coronaviruses that infect humans, it's just that these three have received a lot more attention and funding to study compared to the coronaviruses that cause less severe symptoms.
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If SARS-CoV-1 were spread through encounters, then it should have crossed the species barrier outdoors, since bats (the virus' reservoir) have encounters with other species outdoors. In fact, of all their inter-species interactions, most take place outdoors because when they are indoors roosting, they are far within the depths of their protective caves, where only their fellow bats and some cave-dwelling animals live.
Also, the list of species to whom bats transmitted the virus should resemble those whose habitats are close to, or overlap with, the habitats of bats. Those would be the species with 1 degree of removal from the reservoir -- of course it could then be spread to other species in contact with the 1-degree species but not the bats themselves. But a 1-degree ring of species around bat-colonized caves should be identifiable.
In reality, the other species that bats gave SARS-CoV-1 to were localized within a single market in Guangdong, China (see here). These multiple inter-species crossovers could not have easily happened in the wild, given their vast and not-so-overlapping range of habitats. But when they are all concentrated into a single place, by people who trade in wildlife of various habitats, then these crossovers with multiple species are easy.
The market was not for dead animals being sold for food or their pelts, but a live-animal market for wildlife. It was enclosed and informal, not an open-air market, nor one with advanced HVAC and filtration systems to achieve aircraft-levels of ventilation. So an infected individual was alive, exhaling into the fairly stagnant air volume, from which all the other individuals -- of whatever species -- were inhaling.
As we saw with SARS-CoV-2, the alternative model of "high population density and more frequent encounters" can be ruled out by the specifics here. Namely, because the animals were being sold, they were all caged and grouped by species -- here's a section with a bunch of palm civets, there's a section with raccoon dogs, and so on. Some sellers would only have one of these species for sale, preventing contact with other species.
The density / contact model could only explain the spread among individuals grouped tightly together -- this particular grouping of palm civets in this particular seller's stall. Or if that seller had palm civets and raccoon dogs grouped next to each other, then among that combined population. The animals are not roaming around the market, so they cannot spread it through encounters with any other animals in a different stall.
The only mobile species that could transfer the virus from one place to another within the market is humans -- some guy spends a lot of time in close contact with animals in one place, wanders somewhere else, and spends a lot of time in contact with other animals. However, that would implicate customers or shoppers who spent a long time browsing around the market -- but in fact, it was the workers of the market who made up most of the SARS cases, and they spend most of their time in their own stall tending to their own population of animals. They are the least mobile and free-ranging of the humans in that market.
These facts can be explained, though, by the model of a contaminated shared medium, namely a poorly ventilated indoor air volume. The virus particles get an initial impulse when pushed out of the lungs during exhalation, so they can coast or glide for awhile, in addition to their movement by diffusion. They can -- and do -- travel through space, without needing an infected individual to move around as their vehicle. When an animal, of whatever species, inhales these particles that have traveled far from their source, they get infected in turn -- without an encounter.
That explains why multiple individuals of one species get it, why the same species gets it no matter whose stall they're in, and why multiple species get it -- all of them are connected by the shared volume of enclosed, stagnant air. It also explains why workers get it more than shoppers -- they spend far more time immersed in the market's enclosed air volume.
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MERS-CoV got less attention because the SARS-1 outbreak happened in the wake of 9/11 and the anthrax outbreak, which primed everyone to be more vigilant about a novel respiratory disease that could be spread by terrorists or hostile foreigners. That post-9/11 mood had faded by 2005 or so, and by the time of the MERS outbreak in 2012, it had all but dissipated -- even though this new disease was coming from Saudi Arabia and had the phrase "Middle East" in its name. And ISIS was chopping off heads, not using bioweapons, so there was nothing big in the background to make people pay special attention to MERS.
But it did get scholarly attention because it was another new coronavirus infecting humans, so maybe it could shed light on SARS and help us prevent any further coronavirus epidemics. Nope! They drew the wrong lessons, based on the reigning false model of diseases spread through encounters, and here we are now with SARS 2.0. Again, the current coronavirus is not deadly enough to need to stop society in order to solve it, but the people investigating SARS and MERS should have been able to prevent it, or at least deal with it based on reality after it was already unfolding, rather than continue to treat it as a person-to-person encounter disease, instead of the contaminated shared medium disease that it so obviously is.
MERS' reservoir is a microbat species that prefers shelter while roosting, as usual. (It does have an unusually cool name, though: the Egyptian tomb bat.) The main species it has crossed over to is dromedary camels, and to a lesser extent humans.
With their usual contagion-theory blinders on, researchers focused on the fact that a man who had died of MERS had been in close contact with a camel that was also infected, indeed he had been applying medicine to its nose which showed strange secretions. The inference is that the virus was present in the nasal secretions, the man touched these secretions, and then his own nose or face, which sent it into his lungs, spreading the disease through a close-contact encounter.
But how the hell did the camel get it from the bat? Did a healthy camel sniff a sick bat's secretion-oozing nose? Or maybe the bat felt mischievous and targeted the camel, smearing its nose on the poor camel's nose, while taunting him with, "Now you got my gerrrrms, now you got my gerrrrms!"
One team came close to the truth, when they found MERS-CoV in an air sample collected from the barn of a camel-owner who had come down with MERS, and whose camels were sick with MERS (see here). This proved it could be airborne, that it could stably aerosolize, and that it was at the scene of the crime at the right time.
But as usual, airborne or aerosolized respiratory diseases were treated as spread through close contact, i.e. the proverbial "cough or sneeze in the face". "Proverbial," and yet an act which has never actually happened between two individuals of any species, at any time in our planet's existence. However, it is required by the ideology of ballistic / encounter-based models, so it simply must happen so frequently as to be proverbial.
And again, how could the camel get it from the bat? The human owner was close to the camel -- close enough to be applying medicine to its nose. OK, maybe it spreads directly in an airborne way over a distance of several feet. But bats roost way up on the ceiling of the barn, or high up on one of the walls. The bat was not roosting within several feet of the camel's head. Therefore, close contact (airborne or otherwise) is ruled out.
Only the shared medium model explains the multi-species crossovers. The bat finds a structure where it can roost, and this camel barn is poorly ventilated like all houses for livestock. While roosting, it exhales into the stagnant enclosed volume of air in the barn. While not roaming around outside, the camels stay in the barn breathing that air. The human owner of the camels also spends time in the barn doing various chores, breathing that air -- whether or not the bat is there at that time (it could be out foraging), and whether or not the camel is there at that time (it could be out grazing). Other humans could enter the barn, for that matter (such as a guest who is just chatting with the owner, while both are inside the barn).
Since the aerosolized virus particles get both an initial boost during exhalation, as well as diffusion, they can travel from way up where the bat is roosting, to where the camel is resting, or where the human is doing his chores. The stagnant indoor air connects them all.
A later review article (see here) provides further confirmation of the shared medium model, although it is not aware of that. It looks at various factors to explain why MERS is emerging in the Arabian peninsula during the 2010s. One major factor they point to is the sedentarization of nomadic pastoralists, owing to the immense wealth that the Gulf states (such as Qatar) began to enjoy after nationalizing their oil and gas supplies (mostly completed by the 1970s), and as they began to spend some of that wealth to encourage the nomads within their populations to settle down, so the state could better administer them.
Camels that are part of a nomadic herd do not spend any time at all inside of an enclosed volume of air. There are no permanent structures for dwelling or gathering, and even the tents that are put up temporarily are for people and their things, while the camels rest outside of them. Only when nomads begin to sedentarize, do they build permanent dwellings for their livestock, like barns.
Bats are not drawn to roosting near nomadic herds, since there is nothing for them to hang from on a regular basis. Perhaps their tents -- but those are only good for a short while, and then they're gone. Bats want a reliable den to provide security, not having to tag along with a nomadic group, which would be far and few between. Only the sedentarization of the nomads would bring a structure that would tempt the bats to roost inside of -- the barn (and perhaps the human owner's home, although that space is more vigilantly policed by its dwellers).
Notice again the inability of the contact / encounter model to explain these facts that attend sedentarization. Camels and their owners are in close contact all the time when they are nomadic -- being ridden, being tended to, being shown affection, being milked, and so on and so forth. Whatever pathogens infect camels, have ample opportunity to cross the species barrier to humans. And yet, no MERS-like crossover events among nomadic camel-owners -- only when they settle down and build barns, which does, however, introduce a shared medium that could become contaminated (indoor air).
Contact theory could explain why bats don't spread disease to camels in nomadic settings, because they have no close encounters outside of barns. But the shared medium explains this as well, in addition to all the other crucial facts.
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Let's end with a return to the grand historical view, in which I think most respiratory "diseases of civilization" adapted themselves to the shared mediums that only arose with sedentarization, such as the indoor air of buildings (akin to waterborne diseases arising with public water systems). The case of MERS shows this in-tandem development unfolding in real time, as nomads settled down and instantly got stricken with an infectious respiratory disease.
Pathogens that travel through a respiratory route have almost no chance of spreading in epidemic fashion among nomads, because the currents of a fresh-air environment will scatter them quickly, rather than allow them to build up within a highly-visited space.
Adapting ourselves, and our livestock, to these sedentary environments requires sanitizing them. Not by spraying antibacterial disinfectant on all surfaces -- that's not how they spread. But by treating the medium with a pathogen neutralizer (that has no bad side effects), or creating some kind of current that will carry the pathogens quickly away, or separating outgoing from ingoing channels of that medium.
In the case of contaminated indoor air, the solution is improving ventilation and filtration, to such an extent that earlier times will look as backward as we presently view the public water systems of the pre-20th-century West.