>>11458906There were, but they were mostly before mass worldwide transportation was a thing, so they basically killed off a local population and essentially created its own extinction by quarantining itself due to lack of hosts.
Generally deadly diseases will either work quickly or have noticeable symptoms so these days such a patient would be isolated quickly. If it doesn't work quickly enough we have treatments to lower the mortality rate.
Can't breathe? We'll do it for you. Need to filter blood or get a transfusion? Also available. Need clean fluids and nutrition? Sure thing unless you're unfortunate enough to live in a third world/developing country.
As a slightly related point, the current outbreak is seemingly less lethal to children.
https://www.washingtonpost.com/health/2020/03/10/coronavirus-is-mysteriously-sparing-kids-killing-elderly-understanding-why-may-help-defeat-virus/So some diseases are just oddly picky.
