There had been many incidents in history when people from other continents brought outbreak of diseases along with them (for eg, diseases brought by the Spaniards to the Incas), why such things doesn’t happen today, atleast not on a large scale?
Also I’m not from science background, so sorry if the question was dumb.
In: Biology
In this day and age, with jet travel, most viruses and bacteria that spread human-to-human have already made it around the world and you’ve encountered most stuff that could survive in your part of the world. They’re not too dangerous to you because your immune system has seen it in one shape or form.
There are still plenty of diseases that are still geographically isolated, like yellow fever in tropical areas of Africa and South America, and you are encouraged to get vaccinated for them when traveling there. In the case of yellow fever, it’s spread by a mosquito that doesn’t survive outside of those areas.
People get sick all the time on vacation see; [travelers diarrhea](https://www.mayoclinic.org/diseases-conditions/travelers-diarrhea/symptoms-causes/syc-20352182)
For things that are more dangerous they recommend getting vaccinations.
Further, washing your hands, drinking bottled water… and other basic hygiene tricks are very very effective
If you’re going to certain continents it is heavily recommended to get various vaccinations due to this reason.
Also, I think we can assume that today in the age of globalization, diseases are more spread out. When the Europeans first came to the Americas, lots of natives died due to a lack of immunity. Today, with everyone constantly going to different continents, and immigrants and all that, it’s less of an issue perhaps.
You can and many people do get sick while traveling. But its not like when we were discovering new countries. Back then, people were seperated, so one group in a far land would have their own bacterial culture than another.
Now we travel wide and far frequently. People from other countries come to our own and expose us to those baceria and viruses.
So basicly, on a global scale, the mixture of bacteria is more uniform today than it was in the past. We now have more exposure to a wider array of bacteria that helps boost our immune system against them.
When I first moved to another country and got a cold, it was the worst, most horrible I ever had. After that, though, things got better! It might take getting used to some different biota in the water, but because of vaccinations, there isn’t really much in the way of smallpox, typhoid, etc, in countries like there used to be.
There have been a few examples of this, and it was contact with people unknown for many centuries. That doesn’t happen any more. Sometimes new diseases spring up, like SARS or MRSA, but we have scientific medicine now that detects them and contains their spread.
The flu kills 650K people every year, even with the flu vaccines we have developed. This is more than malaria (585K). The top of the contagious disease pyramid kills a lot of folks, things like yellow fever (30K) of even Ebola (4K) are way down the list. Exotic, new diseases are just very unlikely.
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