Does illness remain in population "just by never going away"?

Submitted by BlackWardz t3_10oe29j in askscience

The question is a bit hectic but I wasn't sure how to word it properly.

Basically if we consider bacteria and viruses causing illness in humans, are they present for so long only because there was always someone to "pass it on"?

In other words, if we were lucky enough to get to a point where nobody would be infected by smallpox, would that mean the end of smallpox? I know there are of course things like the bacteria being able to survive without a host for some time on contaminated surfaces, etc., but hosts remain their main way of survival, right?

The thought that brought me to this question was whether the wide range of diseases we know today exists because we were never lucky enough for nobody to be infected by that specific bacteria for example.

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iayork t1_j6i799b wrote

Some diseases could be eradicated if they were eliminated from every person. But many diseases have reservoirs in the environment (tetanus, Legionella, histoplasmosis) or in animals (West Nile, monkeypox, Ebola, MERS). Other diseases arise more or less spontaneously due to e.g. mutation (feline infectious peritonitis -- I can't offhand think of a human example) or recombination with related animal viruses (SARS, SARS-CoV-2). Since these diseases don't depend on remaining in the affected population, they wouldn't be eliminated by clearing them from that population.

>if we were lucky enough to get to a point where nobody would be infected by smallpox, would that mean the end of smallpox

That's exactly what happened, but there was nothing "lucky" about it - it was the result of a decades-long enormous vaccination and eradication effort by every country on Earth,

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LifeLongNaturist t1_j6kjlsb wrote

And there is smallpox virus stored in labs in Russia and Atlanta for research purposes under the supervision of the WHO. It also has turned up in labs in Philadelphia in 2021 and Bethesda in 2014 as leftovers, could it be in other labs in the world? Hopefully it would be contained quickly if it ever escaped from a lab due to poor quality control, but sorry for those that would be affected.

https://www.science.org/content/article/six-vials-smallpox-discovered-us-lab

The Philadelphia lab virus was later identified as the virus used to produce the smallpox vaccine rather than the actual smallpox virus.

https://www.livescience.com/smallpox-vials-discovered-pennsylvania-research-lab

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jpbarber414 t1_j6i0wag wrote

Yes they are called endemic diseases.

What It Means When a Disease Is Endemic

An endemic disease is a disease that is always present in a particular population or region. Every year, the amount of endemic disease is considered a “baseline” of what is expected to persist indefinitely. Some of the most recognized endemic diseases include the flu, malaria, HIV, and syphilis. Many experts predict that COVID-19 will become an endemic disease at some point.

https://www.verywellhealth.com/what-is-an-endemic-disease-3132825

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theskepticalheretic t1_j6hy5pd wrote

Answer to this is complicated and boils down to 'it depends'.

Hypothetically, let's say a disease has been eradicated. Disease X was present in the population, a treatment and preventative measure was developed and this disease does not have reservoirs in other species. It could go extinct. Conversely, this disease may be closely related to another more benign disease. It is eradicated and the closely related but benign disease mutates to replace its cousin.

Overall the battle against a disease is never really over. The goal is containment and then eradication but eradication is likely never permanent or complete.

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GalFisk t1_j6i7ffp wrote

Some diseases also jump species. Animals can give humans rabies, but humans generally don't pass it on. These often stick around in species that don't get sick, or don't get nearly as sick, as we do. And some can linger, for example anthrax which can sit around in soil for decades, just doing nothing.

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