The basis of a lot of post-apocalyptic fiction is that a super virus or superbug has wiped out most of civilization. How likely is it that a disease has a 75%+ kill rate AND can be transmittable enough to spread very far (i.e. airborne, insects, etc.)?
Have we ever seen a disease like that? The deadliest Ebola viruses aren’t as transmittable, right?
Out of curiosity, do you mean “75% kill rate” when talking about how many of the infected died, or how much of the total population died?
In any case, I suspect that a resurgence of the virus that caused the Spanish flu pandemic of 1918 might come closest to what you’re asking. I am not an epidemiologist (or medically trained in any way), but I’d guess that the infection rate would be much, much higher now because of how much more travel there is, and how much easier travel is, these days than back then.
Actually, some of the deadliest are VERY transmittable; that’s one reason why they don’t spread far ( another being that they are fragile, and don’t last long when exposed outside a body); they kill everyone too fast.
As I understand it, the answer is “certain”, eventually. It’s more a question of whether it will be caught in time, or appear in a place where it can spread far and fast enough to avoid burning itself out. A plague that kills everyone or nearly so in an isolated village Ebola style has little opportunity to spread before being noticed and quarantined, even if it doesn’t just stop because it’s victims are all dead. Some “superflu” that started in some big city and travel hub like New York could easily be another matter; as mentioned, a new version of the 1918 flu would be very bad.
But “very bad” in this case means rather something like 1% of population. Even Spanish flu in most extreme estimations killed 5% - an that was 90 years ago. You know, we have WHO, better medicine, A LOT more knowledge about viruses and no world war on top of that. A chance of global pandemic of disease with 75+% lethality is as close to zero, that you can safely bet your life that it won’t happen.
Maybe, very big maybe, if we acquire more knowledge about viruses and human immunity system, we would be capable of creating such superbug artificially. But it won’t happen tomorrow or even in twenty years.
We also have much more travel, denser populations, and our knowledge of how to actually STOP viruses is still quite limited.
If Ebola mortality rates can hit 80-90% , why is it so implausible that an Ebola virus that goes airborne with higher infection rates might arise somewhere? Given its incubation period of 2 to 21 days, if it achieved higher (and airborne) infection rates during, wouldn’t it be absolutely devastating?
By the way, why have I never heard of the Spanish Flu before? 50-100 million dead? And that was at only 2-20% mortality for those infected? Holy smoke.
H5N1 (avian flu) has near 100% lethality for birds and cats, and about 60% lethality for humans. Bird/Human transmissability is very low, and Human/Human transmission has not occurred. It is highly mutable, and is considered the most likely source of the next global flu pandemic, which could be more deadly than the “spanish flu” pandemic. One problem with avian style flu is that it can incubate and mutate in pigs, increasing the risk that is will cross another species barrier to humans, or combine with a human transmissible virus.
The Ebola virus seems to be more virulent and lethal, but less mutable. It also has a smaller host pool (fruit bats) isolated from other species. So a transmissible Ebola is not considered likely.
Si
During the cold war until 1972, the U.S. and USSR had active Bio-weapons programs. And still probably find ways to fool around with it. Russia too.
There are 8 Countries besides these two with active programs seeking to weaponize biological material.
So, a)I would not be surprised if such a virus did exist today and b) were it to emerge I think the odds are pretty good that man could had monkied it up - that it didn’t emerge naturally.
But, when you take into account with how many viruses global population have come into contact and how few actual pandemies happened, I’d say current procedures aren’t that bad.
Besides, I agree with your main point - that major pandemia WILL happen. It’s just function of probability and time. I just don’t think that it will be like these Hollywood pandemies with depopulated cities a’la The Stand. There will be millions of deaths and severe social impact, just not as severe as popular culture likes us to think.
Exactly, why aren’t there any super deadly diseases with a long enough incubation time that they could spread?
I’m sorry, but I’m not sure what you mean by “virulent”, as distinct from “lethal” and “transmissible”. I thought “virulent” encompassed transmissibility, as well? Also, about mutability, is this a necessary ingredient for having a high transmission rate? Or is this mostly about whether or not it can make a species jump?
Is there some sort of inherent biological contradiction that helps prevent the “perfect” combination from forming? As in, highly lethal diseases (like avian flu, ebola), because of some biological reason (e.g. the way they’re structured), tend not to be highly transmissible or have a high incubation period? Or vice versa?
Ebola is transmissible human to human fairly easily, but only by direct exposure, not via aerosol. Mutability just increases the likelyhood of a virus making the change to one that is transmissible by aerosol, or cross the species barrier.
No actual rules, but there may be some guidelines. Stable viruses give the opportunity for host immunity. You can get pools of partially resistant individuals that act as carriers, which enables stasis. This happens in Rabbit Hemorrhagic fever. After the initial die-off, resistant individuals breed, but carriers still infect the offspring. But I think that a stable, lethal, transmissible virus will kill off the entire host population pretty quickly. Rapidly changing viruses avoid resistance, but easily mutate into less lethal or less transmissible forms. It really is just odds - a super lethal, super transmissible stable virus is possible, just as tossing 1000 heads in a row is possible. Just very unlikely. Which is lucky for all of us.
Si
Thanks for your patience, si. I’m still confused about a few things, though.
So in this instance, you’re referring to the long-term survival rate of the host (human) population? The next generation (after pandemic) will likely pass on their resistance, though the virus will keep going as well, likely causing problems hen they come into contact with people that have not developed resistance.
OK, so if a stable virus is lethal and transmissible enough, I take it that resistance in a population won’t help the non-resistant individuals. If X% were resistant, it’d just kill all the infected at a rate of 100-X% and then peter out? The resistance only helps protect those lucky X%, as well as future generations, right?
And if I get this right, super lethal and super transmissible are possible, but it’s much more likely to happen with a highly mutable virus, since highly mutable viruses just go through many more iterations than stable viruses; they have many more chances to hit the target. A stable virus may hit the target, but, by its very nature, doesn’t get as many attempts over a given period of time. If it managed to hit the right combination, we’ve probably pissed God off and deserve to die anyway. That about right? 
Thats pretty much it. Rabbit Calicivirus (RCV) is a case in point. This is a stable, lethal and transmissible virus in rabbits. It was being investigated in Australia as a biological control, when it escaped into the wild. Pressure was applied in NZ for a release as well. When this was held up, farmers in NZ obtained infected rabbits from Oz and released the virus. Rabbits died, and the virus spread. But due to the mismanaged release and timing, resistance quickly developed. RCV still kills rabbits, but the pool of resistant individuals is growing, and rabbit numbers are approaching the levels prior to RCV. A similar situation occurred with Myxomatosis.
So even stable, lethal, and transmissible viruses may not wipe out a host population.
If there is a reservoir of carriers, slow developing infectious individuals or alternative hosts, then reinfection will occur, as in the RCV situation above. There will always be susceptible individuals with stronger immune systems that can suppress the virus (and survive or become carriers), and resistant individuals that have weaker immune systems that will be killed by a survivable virus. This is why biological control does work, but never as well as people would hope.
Thats it. A biological war between immune systems and attackers in which neither side can get the upper hand.
Si
IANABiologist.
A parasite that kills it’s host just made itself homeless. A rapidly mutating lethal virus would probably evolve into one that’s not lethal.
Also, even the Black Death only had 40% mortality (more or less), and back then the most advanced medical science involved the wrath of God and unbalanced humors.
My understanding (mostly from Barbara Tuchman’s A Distant Mirror) was that the BlackDeath killed a third of the population in its first two summers, and half the popluation by the end of the 1300s, in a series of followup waves.
This causes a lot of confusion. People often cite that the Plague killed 1/3 of Eurpope – it did, but that’s selling it short. It killed that much in the opening moves. Overall it took at least half the population in a fairly short time. Population did not recover until as late as 1600 in some areas.
Sailboat
If I recall correctly, virulence is not the same as contagiousness: the latter describes how likely you are to catch it, and the former describes how dangerous it is once you’ve got it.
The common cold is highly contagious, but not very virulent.
HIV is significantly less contagious, but much more virulent.
(I could be wrong about this; it’s been a few years since my ex-wife, an epidemiologist, explained it to me. But that’s how I remember it.)
I hadn’t heard they’d isolated the host species. When did that happen, and how’d they do it?
Re the Spanish Flu Pandemic, if Wikipedia is to be believed, the stronger your immune system, the more likely you were to die. I am having visions of a mad scientist gene-splicing it with HIV to get folks coming and going. :eek:
Yes. Measles and smallpox (in the New World). Estimated death rates among the indigenous American populations from those two diseases go as high as 90%.
A potentially lethal, easily transmissable viral disease with a reasonably long incubation period (so the infected individuals have plenty of time to spread the disease around before they become obvisouly ill) + an immunologically naive population = bad, bad things. (Heck, smallpox had around a 25% mortality rate among the Eurpoeans of the time, and they had been living with the disease for many generations, and so had had time to build up a reasonably resistant population.)
Sorry, I had meant to say (possibly fruit bats). Nothing definitive.
Si