You're listening to an Airwave Media podcast.

This is the second half of the story of humanity's fight against Rocky Mountain Spotted Fever,

and Rocky Mountain Spotted Fever's fight against us. If you haven't, you should go back

and listen to Part 1 before continuing on. But as usual, here's a recap.

In all likelihood, Rocky Mountain Spotted Fever has been infecting humans in the Americas

for many hundreds, if not thousands, of years.

But we only took notice towards the end of the 19th century.

That was when Europeans first put down permanent roots in the bitter root valley

in the southwest of Montana. Spotted fever is a serious disease any way you cut it. It can cause

deafness, limb loss, permanent cognitive impairment, and even today, it can be fatal. But one of the

most curious things about spotted fever is how variable its seriousness is,

depending on where it's caught. And the strain of RMSF, endemic to the bitter root, is especially virulent.

Historically, between 70 and 90% of those infected died.

I'll spoil this right here and let you know.

Even today, researchers aren't sure why this is.

But a good guess has to do with spotted fever's etiology.

We now know that spotted fever is transmitted by ticks, and it seems likely that this keeps

different strains fairly isolated from one another,

allowing them to evolve different risk profiles.

There are several different tick species which carry spotted fever, and they don't have a lot

of geographical overlap.

And since cases of spotted fever are relatively rare, it must be even more rare for something to catch it from one tick species

...