Why arent we dead yet?

Factual Questions
1

I know, what an optimistic title, but I’m curious why there hasnt been a major pandemic in the industrialized nations?

We’ve had the Ebola virus, Marburg, West Nile, SARS, and far too many others, which have the potential to run wild. Then there are bacteria like the pox or anthrax.

So why have modern society been so successful in preventing a break out? Even AIDS has not affected us as much as Africa and Asia. It is just a matter of better sanitation and hygiene? What percentage of luck is involved, if that can be measured?

And from that very long list on Wikipedia, what percentage of viruses and bacteria are lethal?

AP

2

A general list of some reasons would be that people in richer nations are usually healthier on average with regular access to medication, good hospitals, clean water, and condoms. They are more likely to be educated about ways to minimize the spread of disease.

Well, some of the things on that list don’t affect people. Do you want to know which things have a chance of killing lots of people, or which things could kill anyone at all? For example, a person with a very weak immune system could be killed by a cold, that most of us would shake off without a problem.

3

Actaully there have been pandemics in the industrialized nations. The 1918, and 1967 flu outbreaks are examples. I would say that luck is the main factor. In order for a pathogen to spread it has to be able to infect other hosts before killing its current host.

4

Sorry for the double post, but during the SARS scare, my immunology teacher mentioned that things like genetic drift/shift, and increased antibiotic resistance could very likely create something that would have a very bad effect on our current population.

5

Sanitation and hygene are the major contributors, here. If you look at average life expectancies, they nearly doubled in the space of a few decades when societies began to introduce sewers and running water. Those things alone eliminate the vast majority of diseases that thrive in the third world.

Vaccinations and good pre-natal care is another contributor. The average life-expectancy in third world nations at birth is very low due to the extremely high levels of infant mortality. If you’re lucky enough to reach adulthood, your chances for living longer improve.

That said, there have been some bad epidemics in the industrialized world. The 1918 flu epidemic killed nearly half a million people in the US (out of tens of millions infected). Even that didn’t cause society to collapse.

6

Healthier food, cleaner water, better and more advanced medical care.

To name just a few

7

In Cartoon History of the Universe, volume 3, Larry Gonick mentions (and I don’t know where he got this from) a theory that better public sanitation does discourage more virulent diseases. The theory is that more virulent diseases are likely to kill people. In a society with good sanitation, the bodies aren’t going to sit around for very long for those virulent viruses or bacteria to spread to new hosts, so the really virulent strains of diseases die out. Sounds plausible to me, but IANAexpert on infectious diseases.

8

We also have world-wide organizations which actively watch for signs of a potential epidemic and take immediate steps to stop the disease’s spread before it can become one. If the 1918 flu virus hit today, I imagine the casualties would be substantially less. We’d be better prepared to deal with it and halt the spread even if it did prove to be antibiotic-resistant.

A major epidemic today isn’t* impossible*, of course, but we’ve come a long way since then.

9

I’ll offer some unfounded and (as far as I know) original speculation based on some of Jared Diamond’s theories in Guns, Germs, and Steel. Again, I’m not any kind of expert.

Very few people in a modern western society have any kind of sustained contact with livestock. That’s where a lot of pandemics come from- livestock transmitting disease organisms to people who are in contact with them. Since so few people in a modern western society have such contact with livestock, there are fewer opportunities for organisms to jump from livestock to humans than there would be if most people were keeping a few cows, pigs, or chickens in their back yard.

I’d also speculate that our modern intolerance for pests in our homes has something to do with it. We use window screens or air conditioning to cool our houses in the summer while preventing bugs from entering our homes, so any diseases carried by those bugs have a harder time getting to us. If we have rats or other wildlife living in our homes, we try to do something about it right away, which might not have been the case until fairly recently. That means that diseases carried by those animals have fewer opportunities to get to us.

10

Ultimately any new disease has to come from an animal. However aside from that this piece of speculation makes little sense for several reasons.

Firstly there are indisputably more people in western societies living in close contact with livestock today than there were 200 years ago. The sheer increase in population means that there are orders of magnitude more people sharing a room with dogs, cats, birds and even pigs than there were 200 years ago. So the opportunity for exposure to novel zoonoses has increased rather than decreased.

Even if we confine our defitnion of livestock to ungulates (which is an arbitrary and pointless distinction) there are probably still more people in daily conatct with livestock than there were in the Bronze Age. Once again the sheer increase in the numbers of people almost guarantees this. There are probably more people working in abbatoirs in Europe today than the entire adult population of Bronze Age France.

The other reason it makes little sense is that Western societies aren’t in any way isolated from non-western societies. As HIV, SARS and numerous other novel diseases has proven. If someone contracts a highly tansmissible disease in Thailand or Zimbabwe it will be in Europe or North Amertica within days.

I suspect that alot of the reason why we don’t get pandemics is simply because we’ve exhausted all the best sources. We’ve managed to contract every concievable disease of cattle, camels, cats and chickens and they’ve developed a genetic resistance. There’s nothing left to catch from these animals. For any new pandemic to arise it needs to come from a novel animal soucre or a novel mutation. The scope for exposure to unusual animals like civets and fruit bats which have been the source sof the last few novel human diseases is very low and resulting epidiemics also low. Novel mutations that make diseases particularly problematic are even rarer.

11

I don’t think that Anne Neville’s speculations are quite as far out in left field as Blake suggests. While there certainly are people in close contact with animals, both people and animals in both agricultural and residential contexts are healthier, and sanitation is significantly better, than that of two centuries ago. However, the notion that cross-species transmission has plateaued out has substanial merit. The documented pandemic plagues of Eurasia between roughly 500 BCE through the 17th Century CE mostly had their origins (insofar as we can tell) in viruses and bacteria that originated with or were carried by domesticated animals and exacerbated by high population density of concentrated agrarian and later preIndustrial societies combined with inadequate sanitation. Good sanitation played a part in reducing some epidemics, but many diseases resulted in an effect immediately evident to students of evolutionary theory; infectious organisms killed off those incapable of resisting their effects, leaving a population with a natural resistance to the worst effects, but capable of carrying the virus, while simultaneously excessively virulent strains destroyed their hosts while more moderate versions co-existed and thrived. The childhood illnesses of measles, mumps, and chickenpox (to name a few) are the fortunate successors, well adapted to living in human populations.

There were still, through the 20th Century, virulent infections, the worst of which were influenzas, but modern nutrition and sanitation, along with preventative public health measures limits the spread of such illnesses. Truely virulent viruses like those that cause Ebola, Lassa Fever, and other hemorrhagic fevers tend to kill off their victims too quickly to spread far. Also, having recently jumped from simian species to humans, they don’t tend to replicate effectively, and after several generations the shed viruses tend to be dysfunctional and incapable of sustaining infectious potential. It helps that they also originate in remote jungle environments with limited infrastructure and transportation and rarely spread beyond a few dozen miles before detection and quarantine, but even in an urban environment a non-airborne hemorrhagic fever would probably be limited in impact. (A truely aerosol hemorrhagic fever or a seriously virulent influenza, on the other hand, could wreck havoc.)

In any case, regardless of the infectious organism, 100% lethality combined with high likelyhood of transmission is unlikely, simply because it wouldn’t survive long enough to replicate and spread. Even bubonic plague has a mortality rate of less than 50% when untreated. The only infections that could potentially result in true population-threatening epidemics are probably those which routinely result in meningitis or encephalitis effects, owing to the difficulty of treating or ameliorating those symptoms.

William H. McNeill’s Plagues and Peoples goes into greater detail on the topic of codevelopment of infectious disease and the civilizations of Eurasia, and makes a good companion piece to Diamond’s Guns, Germs, and Steel.

Stranger

12

Exactly, which is why attributing it less contact between species is out in left field. Objectively more people spend more time with animals than they did in the past. So we can hardly attribute the phenomenon to something that we know doesn;t exist.

Attributing it to better sanitation and herd health is certainly plausible, but also totally unconnected to contact time. People can have high contact times and low herd health, or high contact times and low herd health or any otherpmcbination you care to name. The two factors are completely unconnected.

Just to clarify, these diseases are not well adapted to living in human populations. Rather human populations are well adapted to living with them. One only needs to read the documented effects of these diseases on naive human populations to realise the pathogens themselves are still every bit as lethal as they were the day they first crossed the species barrier.

Once again we only need to look at the behaviour in naive populations to see that this isn’ t necessarily correct. While 100% morbidity is ineffective, 99% morbity is a great way for a disease of social animals to spread, provided the survivors are infective carriers for an extended period. As populations collapse the survivors migrate to find other groups to join, taking the disease with them.

Amongst conditioned populations. Very important qualifier there. In contrast bubonic plague and many other diseases have upwards of 7% morbidity in naive populations.

Native Americans and Australian Aborigines would probably have disagreed, having been faced with numerous population-threatening epidemics in great variety.

Once again the important point here is to have a carrier source, either internally or in the form of an immune outside population in close contact. Imagine for example if FIV jumped the species barrier. Every second cat could be a point source of infection, and our cities are full of them. Even if the disease was 100% fatal within weeks to humans it could still easily spread worldwide and survive indefinitely because of the constant infection reservoir.

Fortunately the chances of that happening are slim for the reasons we already outlined.

13

Not as close a contact. You don’t see people doing what old-time peasants were known to do, like let ( smaller ) animals into their huts to keep them from freezing to death, or peasant wives nursing baby animals whose mothers died. Plus, better sanitation and cleanliness means that any contacts we do have are much less likely to transmit anything.

14

You of course meant anti-viral, not antibiotic. Virii are different than bacteria.

15

Everybody I know lets there animals into there huts to keep them from freezing to death. When I was a child I knew a few people who kept large dogs outside all the time, but nowadays it seems like even large dogs are allowed inside houses. DO you really know large numbers of people whose dogs are entirely confined to the yard and never allowed inside?

The breast feeding thing, sure. But then people in the past probably didn’t have dogs sleeping on their beds, so it evens out.

Exactly, so it is entirely unrelated to contact and entirely due to sanitation.

16

There is no such word as virii. The plural of virus is viruses. If you must be pedantic and use the Latin then the plural is virus. If you want to describe multiple virus particles then the term is virions. But virii is never, ever correct under any circumstances.

(This post sponsored by the SDMB Nitpickers Conglomerate and Grammar Nazis Benevolent Society.)

17

Thanks for the good answers. It does seem that sanitation is a greater factor than contact, which helps explain why the most common vector (is that the right word?) now appears to be birds more than other hosts. Even well cared for domestic avian populations easily interact with wild species, fostering transmission. Its also scarier too, considering how far birds can travel.

I am more interested in those strains that would have a high mortality rate among ‘normal’ populations. Unfortunately, it looks like most high-risk groups will always be high-risk. Besides influenza, what does the health community watch out for the most?

Following links, it seems we should be grateful for the seasonal outbreaks of influenza since it keeps the health community eyes open for a pandemic outbreak. But then while we have the resources to watch for an outbreak, it doesnt appear that we have the resources to fight it if it does become pandemic.

And the more I read about SARS, the more I am amazed by the doctors/scientists/administrators, etc. of WHO, the CDC and their sister organizations in how fast they identified and contained that outbreak. They are all heroes in my book.

And have we learned anything more about the cause of English sweats?

18

Not suggesting this is wrong as i don’t know any better but i’m curious about this. Can you explain why this is? What exactly is meant by a *new * disease? Are we just talking about new to human population as a result of an animal disease mutating such that it is now able to infect humans? If not, how can there be new animal diseases but not new human ones?

19

Besides the good reasons listed I would develop Friedo’s thoughts on vaccinations out a bit more:

“Almost”? “Virtually?” all large poultry farms in the United States vaccinate their birds against influenza… different countries have different rules on this - but it is safe to say “many” industrial countries do this.

Further many flu vaccinations (which usually protect against the top 2-3 strains expected in the world that year) for humans and poultry will offer partial protection against new or unexpected strains - so that even if an inoculated person gets the flu he/she will often have a less severe bout than they might otherwise have gotten

Let me note too Influenza infects many animal species but really it is a bird disease, with variants and subtypes that can infect mammals: All known influenza subtypes are found in birds but not all subtypes are in mammals. Really the best guess on where new influenza viruses more usually than not comes from:

In Asia a pig catches an HxNy virus from a bird, and the pig passes it to humans.
It can go vice versa too and does - or two different types of flu mix in a person/animal. And in fact, it doesn’t have to shift in animals it can shift entirely in humans (or be transmitted directly bird to human ) but that is not the usual model

This paper speaks specifically about the 1918 “Avain Flu” and also touches on the above – it is a pretty famous paper.

20

Well, any viral or bacterial infection has to come from somewhere, and that somewhere is an already existing viral or bacterial population. And that population has to exist somewhere, and the place that population exists is in various animal species. Humans are one of those species. But diseases that already affect humans aren’t new diseases, but old diseases.

Now if a human virus mutates and causes new symptoms, we could call it a new disease, but more likely we’d call it a new virulent strain of an old disease. But more virulent human diseases aren’t as likely, because humans evolve resistance to diseases and the viruses evolve less virulence. So an entirely new disease won’t come from an already existing human disease, but rather an animal disease that jumps from that animal species to humans. Of course it works the other way around, a human disease could jump to animals, and an animal disease can jump to another animal species.

FIV (feline immunodeficiency virus) is an interesting example. It’s a very serious disease for domestic cats, but there are wild cat species where pretty much every member is infected with FIV but show no symptoms. Those species have been infected with FIV for a long time, and have co-evolved resistance to the disease. And domestic cats will eventually evolve resistance too. Even if we wiped out FIV in all domestic cats (which in reality would be almost impossible, FIV is a pandemic among cats) it is very likely to jump back to domestic cats wherever domestic cats are in contact with a wild species of carriers.

Anyway, new diseases are overwhelmingly likely to come from an animal disease reservoir simply because there are thousands of animal species and thousands of animal diseases. And we’re not very likely to notice if a human disease jumps to an animal species unless that species is economically important to us.