Is non-manmade pandemic a realistic threat to modern first world?

Question

Inspired by this question, and my own answer to it: Avoiding galactic pandemics. World ending pandemics are a common disaster/after-the-end story trope, I'm trying to determine if plausible, and how one could occur.

What is the threat of a pandemic occurring in a modern first world nation, and if one is plausible then what conditions are required to make it occur? Keep in mind I'm talking about trying to stay to the realm of realistic science, in particular only diseases that plausibly could evolve in the first place.

I define a pandemic for this question as:

1. Naturally evolved, or at least not intentionally man-made. I'm willing to accept diseases that evolved due to accident's or mistakes made by man, such as breeding antibiotic resistant bacteria via overuse of antibiotics, but no weapons-grade engineered diseases.

2. Disease must spread for at least half a year without being contained

3. Has a mortality of at least 10% (ie kills 10% of total population)

4. Is a threat to modern-day first-world countries that aren't willfully ignoring the threat (like some African countries are doing with AIDS).

How plausible and what is the threat of such a pandemic?

Edit: Just to clarify, my interest is not in what sort of virus could be a threat, but how realistic such a virus existing would be! I am particularly looking for information about the likelihood of any suggested virus actually occurring.

Most relevant, the 'ideal' virus is one with a long incubation period and one that is not obviously lethal until long after symptoms are seen. However, I believe the more lethal the virus the shorter the incubation and quicker the time between symptoms and death would be. So if a virus must have a long incubation to be dangerous, I would appreciate at least addressing the likelihood of a long-incubation virus evolving.

Answer 1

A pandemic of the size you asked about is a credible threat. I've seen articles over the last couple of years where researchers attempt to model the spread of diseases and what affects how quickly they spread. The US CDC spends a lot of time thinking about this kind of thing. Given the diversity of research institutions who are working on understanding the spread of disease, I think the threat of a pandemic is a very credible.

[Update for Oct 2021]: And COVID-19 proves my point about pandemics as credible threats. If COVID were a bit more lethal, we'd be in real trouble with much higher casualties. Also, my original post didn't account for the effects of politicisation of the pandemic and those who will prioritize something other than making the pandemic end as soon as possible.

The problem with short gestation period diseases is if you, as the disease, kill your host too quickly then you don't get a chance to spread yourself around as much. Diseases that kill quickly typically turn into diseases that don't kill too quickly because a fast-killer doesn't "survive" long in the population while tamer mutations have more time to expose other hosts. A virus will change over time in relation to the selection pressure of a host's immune system (herd immunity may play a factor too). The longer a virus survives and the more hosts it infects, the greater the chance for mutation.

There's this article from 1999 that talks about mutation rates in RNA viruses. (I'm sure there are newer, better articles to be had.) The mutation rates are stupid high on the order of around 75% per genome per replication. The mutation rate is much lower for DNA-based microbes (including both viral and cellular organisms) at .34%. The authors of the paper state that these numbers are hard to gauge because the mediocre quality of the data. If that's just one nucleotide involved in the mutation, at trillions or quadrillions of replications across many different hosts, there will be mutation.

Older Answer to the Question The ideal pandemic agent might have the following characteristics: Make the virus airborne, highly contagious (requires very small doses for infection), contagious shortly after infection, and a long gestation period in the months or years range before it induces acute illness/death. Basically, airborne HIV.

Virus based diseases such as HIV, Ebola or influenza have historically been very difficult to study based on how long it takes for effective treatments to appear after a virus discovery. We've known about HIV since 1980 but it took years to develop effective treatments. If this is a brand new disease then it will take a while for medicine to learn how it works and develop an effective treatment thus giving the disease plenty of time to spread. Ebola treatments are relatively new but medicine has known about it for decades (the Hot Zone was published in 1994). While the pandemic doesn't strictly need to be virus-based, having it be so decreases the changes of rapid effective analysis/treatment by the CDC or local equivalent.

Let's assume the following characteristics of this virus:

• Average gestation period: 6 months, standard deviation of 2 months.
• Illness Rate: 50%
• Fatality Rate: 10% (per your question)
• Required dosage for infection: 100 viruses.
• Time to contagious: 3 days, standard deviation of 1 day.
• Symptoms: Flu-like, coughing, aching, runny nose, headache, fever.

Plausible Scenario: Disease originates in sub-Saharan Africa (sorry Africa). Patient Zero catches the disease from infected pig meat. The virus causes minor inflammation in the nasal cavities, thereby inducing sneezing. It is passed to a foreign aid worker who is about to finish their tour and go home to California after stopping off in London and Paris to visit relatives. The aid worker sneezes on the plane without covering her nose (shameful). The water particles from her sneezes spread the virus to everyone on the flight. In 2 to 4 days, all those travelers will infect the people they know. Even if a person sneezing in a huge airport like Heathrow only infects 10% of the people moving through then that's thousands or tens of thousands of individuals infected. And, people flying through Heathrow go literally everywhere on the planet. People working in the airport will contribute greater still to the infection rates as they have a persistent presence to keep recontaminating the airport.

After stopping off in Paris and London, she heads home to California. The virus is still undetected and unknown. There are no quarantines for infected individuals, no blockades of infected countries. Assuming she has layovers in JFK in NYC and arrives in LAX, two of the largest airports in the US are now infected.

I think you can see where this is going. If nothing else, this kind of a disease is a special threat to the First World because of how interconnected those countries are and the common use of air travel. The power of the CDC can't help you if the virus is unknown.

Compound the effects of this new virus by having the virus start spreading in May/June/July. The 6 month gestation period will coincide with flu season and that will complicate treatment because doctors will think that people are getting sick from the flu, not this new virus. It will appear to the public as a terrifying flu season because people are getting sick and dying from the flu or something like the flu but the flu shots aren't working. The usual methods of quarantine for flu patients won't work because practically everyone was infected months earlier.

What makes this scenario plausible is the high degree of interconnectedness in the First World because of air travel. It's an epidemiologist's worst nightmare to have a lethal, airborne virus that gets spread around by air travelers coughing and sneezing on planes.

Answer 2

The Spanish Flu came close to your specifications, with a few qualifiers.

• It was almost a century ago. The state of the art has progressed since then.
• It was global. Aggregate worldwide numbers mix industrialized and underdeveloped countries.

That being said, the Spanish Flu came within shouting distance of the scenario you asked for. So a similar pandemic, slightly more lethal, slightly more infectious, would fit the requirements.

Consider how legal and illegal immigration bring people from the "second" and "third" world to the "first" world. Say the fictional disease has a longer incubation period, and an outbreak in Central America or Africa would trigger mass refugee movements. How soon could and would borders be sealed? The Israelis in the movie World War Z allow uninfected refugees in to reduce the number of potential infected outside -- cold calculation and compassion working hand in hand. The border defenses will always leak ...

Answer 3

There are three ways diseases can be highly lethal I can think of right away and one of those ways would take a long time to show symptoms. Basically, if the disease kills by causing gradual irreversible damage, the ability of the body to compensate for it would hide it until the amount of damage exceeds the ability of the body to compensate. Disease like this might take years to kill, it might even be difficult to connect the increase in deaths to a specific pathogen. This is because there would be lots of infected that would show no symptoms of the lethal disease and also people dying from the disease whose bodies had already kicked out the pathogen.

In a case like these there would first be a mild "flu like" disease spreading and after it was found the symptoms are no different than other seasonal flus, largely ignored.

Then after a few years people would start dying from a weird disease there some critical system starts simply failing. The first victims would be the old and those whose health was weakened by some other disease. There would be a large hunt for the reason. Maybe people are eating too much food additives? Maybe that new bio-diesel really was not that good an idea? Maybe those nuclear tests in the 50s and 60s permanently damaged the people born at the period? It would be difficult to home on to a single reason since realistically people dying in the first wave would be dying because of a combination of factors. If the pathogen was virulent enough it could be so common that noting it was present in most of the victims would be meaningless. And there would certainly be some cases where doctors would miss that the person had been exposed to the pathogen.

By the time somebody connected all the dots it might be possible for the majority of mankind to e infected and have sustained enough damage for that to be lethal. You could have a death toll exceeding 80 percent

The downside of this form of infection for fiction is that the 80 percent lethality might not make that much of a difference. It is easy to forget, but despite modern medicine nearly one hundred percent of people die. Often of some disease. So this kind of pandemic would simply have the effect of shortening the life span and giving developed countries, the first world, a population structure similar to one in the developing countries. In that sense it really would impact the first world much more. Which is a plus?

Exact effects depend on how fast it kills. If it kills slow unless you are already sick in some way, it would just change the population structure. There are people who complain about the direction the populations in developing countries are going, so this might not be all bad. If it kills everyone, no matter how healthy and young, within some relatively low number of years, you'd have a real pandemic in every sense.

Answer 4

I am no specialist, but I think a pandemic must be based on a virus: it spreads easier, and harder to fight. Plague, e.g., can be countered with antibiotics.

Against viruses, we have currently two weapons:

• Quarantine
• Vaccines

Now, I think viruses have the following characteristics

• Incubation time: time between exposure and symptoms,
• Contagion time: time between exposure and when the affected person is contagious,
• Propagation: means and effectiveness,
• Fatality: number of victims succumbing to the virus.

We can then consider recent virus epidemic/pandemics:

• Influenza H1N1: it is very contagious, the 2009-2010 reached 10-500 million people (more than 200 countries affected), and the 1918 (Spanish Flu) affected 500 millions. It can be transmitted through the air (coughs, sneeze), which facilitates its propagation. However its fatality rate is quite low (0.03% in 2009-2010).
• Ebola: it is transmitted through direct contacts which limits its propagation. However the fatality rate is up to 70%. Even in 1st World countries (Spain, USA), some patients died from it in the on-going pandemic.
• Influenza H3N2:the mutation of the virus "surprised" the experts, as a result of which many cases were observed this winter as part of the seasonal flu. It is considered somewhat deadlier. But I couldn't find any satisfying statistics.
• Influenza H5N1: the avian flu is deadlier than H1N1, with more than 50% fatality rate. It mostly affects birds but can sometimes be transmitted to humans. The pandemic in 2006 affected a considerable amount of birds. But luckily for us the transmission from birds to humans is quite low.

Where does that lead us to find a killer virus? Well I think it can be seen that typical influenza spread very fast. But their incubation time is about 1-3 days (as per the link you shared). And their mortality rate is pretty low. By keeping people at home when the symptoms appear, the progression is limited, and due to good medical conditions many death are avoided (see below). Ebola on the other hand is quite slow. It cannot be transmitted by droplets from coughs and sneeze. And its incubation time is up to 20 days (or even more). However its fatality rate amounts to more than 50% even in medical centres.

Therefore, consider a deadly influenza mutation which increased dramatically the fatality rate, without lowering its transmission mechanism. You got yourself a very touch and deadly virus. Without going too far off in imagination. Is it enough to kill the close to 100 millions (10% of the 1st World)? I doubt it.

For most influenza case, we have vaccines to prevent them (if you do get vaccines). Otherwise, and for the other viruses, isolation/quarantine is the best option. As soon as a patient develop the symptoms, s/he is isolated from other people to limit the propagation of the virus. However, what would happen for an hypothetical virus, where people get contagious as soon as (or even before) the symptoms (fever) are noticed? Isolation would still be effective, but not as full-proof: neighbours might have been contaminated prior to the isolation.If the propagation medium isn't too restrictive (unlike, e.g. HIV and more like influenza), the quarantine approach would be limited. Which would still have a large spread (similar to the H2N3 of this year flu) in the 1st World. And if that virus is combined with a high fatality rate, you are in for a disaster.

This is as much as I see, without much prior knowledge and extrapolation.

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But now consider an alternative scenario. In the 1918 Spanish flu, which was an Influenza A(H1N1), most of the victims did not die directly from the flu itself, but more the flu lowered the defence mechanism of the body, and they died, e.g. of bacterial pneumonia.

So just hypothetically, consider a strong H1N1 pandemic couple with a plague or other bacterial-based pandemic. That would probably be pretty bad.

Answer 5

I had an idea about this. I'm not sure exactly how plausible it is, but it is inspired by hypomyces. The disease doesn't affect humans DIRECTLY, rather, infects and mutates other viruses. So, you take a virus which is difficult to treat, such has herpes which already infects some 90% of the population and the theoretical virus would be easily overlooked because it has no effect on human tissue directly, instead causes herpes to become a cancerous flesh-consuming blight. makes me shutter.