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Diseases that cause changes in the behaviour of their hosts are nothing new. Rabies causing animals to bite others is the best known example, but there are plenty of other (often nightmarish) behaviour-altering diseases.

Scientists have discovered a disease, called “Change Of Vacation: International Destination”, that causes its human hosts to travel more than they would normally. They are not sure why it is doing it, but they suspect it is to ensure that it does not "die out" after infecting everyone in a local community.

How is the disease changing the behaviour of its hosts so that they travel more?

Preferably this disease is caused by a virus, but it is not a hard requirement.

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    $\begingroup$ This disease can surely change behavior, but only on an evolutionary timescale. And it will never be clear what mechanisms it uses without long-term, in-depth study. This isn't a process guided by intelligence, so it's not seeing some clever little button to push in the neurochemical land. If it expresses this gene a little more, and another gene or two a little less, it's more successful on a statistical scale. And it keeps adapting. The answer's largely the same for non-viruses. $\endgroup$ – John O Mar 28 at 4:42
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    $\begingroup$ Try to be sharper in your definition: any diseases/wounds requiring treatment cause an increased travel to the receiving subject, starting from reaching the medicine box to fetch a band aid to going to the hospital for staying in the ICU $\endgroup$ – L.Dutch - Reinstate Monica Mar 28 at 5:43
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    $\begingroup$ We know that zombies travel much more than non-zombies, shambling unceasingly across the Earth, day and night, in an endless quest for yummy braaaiiiiiinnnnns of their prey. $\endgroup$ – user535733 Mar 28 at 15:28
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    $\begingroup$ No! Bad! Do not give the viruses ideas. They are listening to everything we say! Shhh! *puts tinfoil hat back on* $\endgroup$ – Cort Ammon Mar 28 at 21:56
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    $\begingroup$ Can't answer, but I may have that disease. $\endgroup$ – WGroleau Mar 29 at 16:50

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Many elderly people get something similar - the feeling of "not being in the right place", usually in their case because the "right place" would maybe be their childhood home, or the house but like it was twenty years prior. So, they start expressing the desire of "going home" (and, often, wander in search of it).

This feeling is linked to the levels of two neurotransmitters, dopamine and serotonin. Alter those, and very little is needed to start the wandering impulse.

Also, traveling abroad will alter the circadian rhythms, which changes the activity pattern of the front hypothalamus suprachiasmatic nucleus (SCN). This in turn increases the synthesis of melatonin and other hormones and makes "having traveled far" detectable at a biochemical level.

So what the virus or agent needs to do is to depress the dopamine/serotonin cycle subject to a melatonin production level below a certain threshold so that the victim will experience intense boredom, unhappiness and desire to escape, but with a boost in energy levels to enable them to do something instead of falling into depression and apathism.

If and when circadian alteration is detected, the cycle will revert as far as possible, a sort of "recompense mechanism". Affected people will get "itchy feet" (or maybe it is called "cabin fever"?) and wander around. Those who move far enough will experience relief and a general sense of well-being the farther they go, thus positively reinforcing the "traveling" compulsion. After a while, the impulse to relocate will reappear.

You won't be able to have victims climb to a precise height and die there, but as far as traveling goes, that's doable.

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    $\begingroup$ What you describe is a side-effect of Dementia, which is the various types of forgetfulness (the most well-known being Alzheimers) which come with age. Having worked with elderly people most of my life, I can tell you that this can be a very driving need for some people; for example, I once helped take care of an 80-year-old German war bride who was always going on about how she needed to go home (to Hamburg, specifically) so that she could be with her mother (who had died ~30 years before). $\endgroup$ – The Daleks Mar 28 at 19:54
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In vino veritas (in wine lies the truth)

There is a genuine albeit extremely rare condition called auto-brewery syndrome. In very non-technical terms, an affected person has fermentation occurring in their gut to produce ethanol, which then intoxicates the person as if they had ingested alcohol through more conventional means.

Imagine a virus that is spread by touch or body fluids that induced severe auto-brewery syndrome, not continuously but cyclically with increasing peaks. The cycles are over a period of several days - so a patient gets drunk, then sobers up and shows no sign of auto-brewery syndrome, then several days later gets more drunk and so on, until eventually the ethanol dosage is at toxic levels. Every time a patient is in a "drunk" phase they are likely to spread the disease through contact with others by ignoring even normal personal space limits and/or by infecting those who restrain them when they become too obnoxious.

Now we put patient zero in a fairly affluent society but one with strict limits on freedom of speech, maybe even a social credits system of some sort. Patient zero is at work when s/he ignorantly becomes roaring drunk and lets everyone know what s/he thinks of the available equipment, the manager and the ruling body of the country. During this rant, lots of people are touched and infected as patient zero staggers around. S/he is not preaching revolution or sedition so the police are not called on the spot, but when patient zero sobers up s/he decides that taking an overseas holiday or emigrating would be a really good idea. This process is repeated for a fair proportion of patient zero's co-workers and family who were infected when they behave similarly in the next week - as the initial response is very likely to be a police investigation anyone who has any sort of a guilty conscience and enough money is going to run for it.

Now let's look at what happens to patient zero and the first few cohorts of infected people. They arrive in their destination countries of first choice and proceed to make even worse drunken asses of themselves. Repeatedly. Due to this behaviour they either are deported or flee voluntarily to their country of second choice before they can be deported, infecting more people along the way.

Intermittent drunkenness is not likely to be recognised as a transmittable disease for a considerable period. (Sustained drunkenness would be recognised quickly - as soon as the police put someone in the cells to sober up and they were still drunk 12+ hours later there would be a doctor called in who would be comparing notes with other doctors very quickly.) By the time this disease is recognised as such it would be able to spread very widely.

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  • $\begingroup$ even an intermittent auto-brewery syndrome is going to be discovered, though it does create enough delay to help spread the disease - and, even more importantly, to find all of the victims even after the disease is known to exist. $\endgroup$ – John Dvorak Mar 28 at 20:49
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    $\begingroup$ A limeric: There was a young lady of Ryde, who ate three dozen apples, and died! Inside the lamented, the apples fermented: making cider inside 'er insides! $\endgroup$ – Jasen Mar 29 at 4:58
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    $\begingroup$ @JohnDvorak I agree that once the disease is identified it will be comparatively easy to identify the victims, but it will take time. Contact tracing will also be complicated by the inability of even a helpful victim to remember accurately who they may have come into contact with. $\endgroup$ – KerrAvon2055 Mar 29 at 5:04
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    $\begingroup$ @KerrAvon2055, just do it the South Korean way and track every mobile phone. $\endgroup$ – Separatrix Mar 30 at 7:59
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Vivid dreams at night and dull bored feelings by day? The virus may affect your dopamine levels, you need to produce it in larger quantities or die in a depressive episode (i.e. eliminate yourself from the gene pool). Your brief profile as a survivor: you need to feed on new experiences all the time to feel alive; you may even refuse/ignore the closure of Bondi beach. Of course, an enhanced libido may allow you to survive longer - you will search for new sex partners; nothing personal, you're just meant to infect them.

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Paranoia

There are many causes of paranoia but for our purposes drugs, such as marijuana, would be a good parallel and gives a good two stage hit. The disease interacts with the endocannabinoid system in much the same way that marijuana does - making some relaxed and happier and inducing paranoia in others. The relaxation helps spread the disease to others as they get closer whereas the paranoia only increases until the infected flees their current environment under the impression they're being followed.

As the initial phase subsides those who were initially mellowed now begin to experience the paranoia as their relaxation leaves them and withdrawal begins. Not all infected will experience such extreme paranoia that it drives them to flee but enough will that it can drive some infected abroad and spread the disease there.

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  • $\begingroup$ Paranoia may but also automatically generate "social distancing" ... $\endgroup$ – Hagen von Eitzen Mar 28 at 20:51
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Escape!!

As has been suggested in Italy, early notification that there IS an outbreak of the disease, and that a quarantine IS impending, was enough to make people evacuate the quarantine zone.

Downside there is that some of them were already infected/contagious, so carried the disease onward out of the quarantine zone.

A simple human-nature response of "lets get out of here before the lockdown" is enough to spread the disease more, further, and faster than otherwise.

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    $\begingroup$ On re-reading, this is a bad fit answer, because its based on human nature and not on changed brought about by the virus/disease. $\endgroup$ – Criggie Mar 28 at 23:49
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    $\begingroup$ it is totally brought about by the disease. People would not flee if folks around them were not dying. If you need it disease based, have the disease elevate epinephrine levels: more fight and flight. Which for this means flight! $\endgroup$ – Willk Mar 29 at 2:18
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    $\begingroup$ @Willk it's not a change to normal human behavior caused by the disease. It's normal human behavior which would happen regardless of whether someone is infected or not. $\endgroup$ – barbecue Mar 31 at 2:01
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Carownervirus

Pathogen that prefers warmer, carbon-rich atmospheres to multiply in. Alters human endorphin production [1] to be happier when producing such atmospheres. Hosts feel happier and happier when driving their vehicles more and further to produce larger volumes of greenhouse gasses. Slowly and without anyone really noticing, human society is impacted to such a degree that normal human life can no longer be sustained (kind of a slow burner novel though!), civilization crumbles, virus achieves 100% coverage, humans die out but atmosphere is now at a high temperature and very high carbon level, greenhouse effect means that this is now self-sustaining. The virus now has the perfect environment to evolve to next stage.

Influenzer

Pathogen that consumes dopamine. It is well understood that posting the next Instagram hit, seeing those likes rack up, provides more dopamine than is found in consuming such media. In the social media-governed world of the "future", influencers are driven to keep posting ever-more FOMO inducing content [2]. As the host body changes to service this new situation, the level of FOMO-inducement required to produce the same amount of dopamine increases, inducing the host to travel further and seek out ever more thrilling locations, activities, and full moon parties, thereby spreading to more people in more countries #vanlife.

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Wanderlust and Claustrophobia

The virus affects brain in such a way as to cause immense dissatisfaction with one's current surroundings. For people who can afford travelling, this may result in increased likelihood of picking exotic vacation destinations and/or long-distance travels with multiple stops, but it also works on a smaller scale: Infected people will feel extremely uncomfortable in confined spaces and will show an increased preference to spending time outside their own home.

Quoting from Wikipedia:

Wanderlust may reflect an intense urge for self-development by experiencing the unknown, confronting unforeseen challenges, getting to know unfamiliar cultures, ways of life and behaviours or may be driven by the desire to escape and leave behind depressive feelings of guilt, and has been linked to bipolar disorder in the periodicity of the attacks.

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  • $\begingroup$ How is claustrophobia compatible with people wanting to spend hours in a flying sardine can ? $\endgroup$ – StephenS Mar 29 at 0:50
  • $\begingroup$ @StephenS maybe they’ll choose cruise ships instead (unless they’re also claustrophobic). $\endgroup$ – Andrew Grimm Mar 29 at 4:08
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How is the disease changing the behaviour of its hosts so that they travel more?

Werewolf Syndrome.

Every few months/years the human blacks out, goes stark raving nuts, and murders his family. After that he's inflicted with paranoia (someone did this to me, there's no way I would have a fair trial), and he flees to a new location.

At that point in his cycle he becomes very outgoing and friendly and rebuilds his life.

The bite of a werewolf does in fact create a new werewolf, but so does having sex with them while they're in their friendly phase.

Of course this leads to all kinds of confusion, the wife kills the husband who himself had a history of this sort of thing. And the rate of transmission needs to be low enough that it doesn't make everyone a werewolf but whatever.

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In the darkest months up here in the north or when its been cloudy for weeks, I get one thing stuck on my mind: Travel to sunnier places. Either south or to the mountain. So consider a disease that makes grey days feel even greyer, and you get less out of sunlight than normal.

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Your description makes one implication, which may be misunderstood. Regardless of how wildly unimaginable the behavior-changing disease effects may be, the causative factors/parasites don't really understand that they are altering the behavior of their host.

Viruses, for example, don't really have any intelligence, they are simply constantly changing, some of their forms seem to exhibit a specific response in a series of hosts, and that's how they come to be. We interpret the behavior-altering symptoms by ourselves, but that was not a "goal" of the pathological causative factors at all. The entire process is driven a lot more by chance (if not entirely), than by intelligence.

Speaking as such, the travelling behavior pathophysiology can be more "cynically" tracked down to some more classical system. Which leads us to:

The Vestibular System is your target. The system that informs the brain (among other things) about the current motion status of the body (linear accelerations, gravity, rotations in various planes, etc.). The vestibular nerve transmits information from the otolith organs to the brain. As you probably expect, the involved mechanisms are extraordinarily complex, but you can definitely "invent" a mechanism that is quite plausible. A trivial example:

The nerve transmits sensory information related to the motion state. Therefore, when relaxed, no information is transmitted. Your virus could, somehow, reverse this mechanism (there can be plausible ways for this), so that the nerve fires when you are not moving and fires a lot less when you are moving, i.e. motion inhibits the neural cells.

You can see where I'm going with this! If patients feel irregular motion patterns when they are standing still, and stillness when they are moving, then they may become dizzy when standing still and the only thing that can help them relieve the dizziness is motion. Therefore, patients will seek to be in motion as much as possible. Tune the effects down a bit, so that dizziness does not set in very quickly when someone stands still, and you will have a fair balance of people that feel strongly annoyed when not moving, and will have to move often to feel relieved. Slowly, it will not be uncommon for victims to try to spend many hours in moving vehicles, airplanes, etc.

So, travelling is not "intended", but helps to relieve the symptoms.

The only drawback with this "theory" is that a fair level of medicine can, at least, trace that down to the vestibular system, because travelers practically "know" why they are travelling. Maybe you can fine-tune the symptoms a bit more, so that it is not entirely clear to those affected about why, but they do feel a significant ease and wellness when in motion!

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It makes you seek warm climates

Perhaps it subtly interferes with temperature sense and pupil dilation, or with melatonin production.

Regardless of mechanism, the net result is that one of the early symptoms is that its victims begin to feel as if they live in a cold, dark place, and so seek out bright warm climates.

In order to be successful as a disease spreading mechanism, it doesn't have to affect everyone the same way- it just needs to affect a significant number of people from disparate places to travel to the same place.

So although this does not affect people who already live in warm climates in the same way, it does encourage people from cold climates to visit popular vacation destinations, thus causing an abnormal spike in local population density, which aids in the transmission of the disease. The infected infect other vacationers, who then return home, spreading the disease far and wide.

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I like the idea of a virus or bacteria that cycles through excreting different "party" drugs. Here are my thoughts:

Increase Openness to New Experiences

A well known affect of psilocybin (the drug found in magic-mushrooms), is that it creates a long lasting openness. Microdosing this with a virus inside you and the openness might be more longer lasting. This will make people want to experience new things such as travelling.

Energy to Move

The disease could then releases a drug like cocaine, amphetamines or even just caffeine to make people more active. This will encourage them to get off the sofa and not just enjoy psilocybin induced trips on the sofa or in the garden.

Meet New People

How can we make people interact more? Easy, there's a well known party drug for that too: MDMA. The parasite can finally secret MDMA into its host so that when people are out-and-about, they then want to interact with people intimately, thus spreading the disease more easily.

The interesting thing here is that scientists have engineered bacteria that can produce psilocybin, so there is scientific grounding for potentially infectious organisms producing some of these chemicals. What's more, if scientists are doing it, what is stopping back-alley chemists/biologists from doing the same? This could be the mutated experiment of a genius drug cook/biologist which might give an interesting back story to a main character.

Finally, I think and interesting idea could be a symbiotic relationship between several parasites that each create one of these chemicals, making it harder to vaccinate against.

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This kind of happens. Some infections affect specific organ function driving animals to e.g. seek and remain by large quantities of water which, particularly in some areas, drive those animals into close proximity with other animals for longer periods of time.

Maybe a slightly more advanced virus could do similar by driving a person to baser/pathological cravings/imperatives (must drink, must flee/hide, must eat brains, etc.), possibly at random or on a loop.

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