[bannie]

You seem to have a good handle on this...

Isn't it true that it still exists in the Steppes (?) east of Europe and in the mountains just west of the San Joaquin Valley in California (just west of ME!)?

Every so often, we get warnings about feral critters being particularly pesty.

[Billthedrill]

Absolutely. The original plague reservoir was in Central Asia, from which it spread via caravan and ship to Genoa in 1347, thence to the rest of Europe. That reservoir still exists; that is, the organism still causes periodic plagues in the host animals, some of whom are resistant, and the population goes down and up accordingly.

In the 19th century we imported Chinese labor to work on the railroads (and other things) and there was a burgeoning population of illegal immigrants in Chinatown in San Francisco. They had their own little private epidemic; private because as illegals the sick and the dead were hidden from the authorities. From there it spread to the population of small rodents that is the disease's natural reservoir, and slowly it spread toward the large population of prairie dogs in the southwest, where today that area comprises the world's second plague reservoir.

It's a dangerous disease for two reasons - the organism Y. pestis reproduces very rapidly in the body, and it has an endotoxin that causes severe anaphylactic shock - headache, fever, chills - which is actually what kills. You sock it with too high a dose of antibiotics and it can actually make the shock worse.

Nobody diagnosed in time should die these days, but the catch is "in time." Too late and it's still a 14% fatality rate. Consider that at its height in Europe it was 30-40% fatal. If it hits the pneumonic form and spreads as a respiratory disease fatalities can approach 90+%. It's nothing to take lightly.