I’ve Googled around a bit and found all kinds of information, except what was it that made it have such a high mortality rate.
I can see how the pustules could be fertile breeding grounds for secondary infections, but was that it–or was it something else that the virus did. (The photos showed why it could be so dramatically disfiguring. Yow!)
Anyone???
From what I can gather, death came from either secondary infection or internal bleeding as the disease wrecked havoc with the organs. Either way, it must have been a truly horrendous way to go.
My great uncle’s entire family (husband, wife, and six children) were killed by an outbreak of smallpox in 1873 (I know this because I have a copy of the accounting of his estate - such as it was. Everything that was of any value was sold to provide nursing care - everything else was burned).
It’s the fever, bleeding, vomiting and diarrhea that would kill you.
Interesting question.
According to The New England Journal of Medicine (April 25, 2002),
I interpret this to mean that i) the effect of the virus is to activate diffuse body inflammation, and that this is exacerbated by ii) the body’s own antibody response to the infection. The net effect is low blood pressure, kidney failure, and presumably also fluid accumulation/inflammation in the lungs.
Note that hemorrhagic (bleeding) smallpox is rare (< 3% of cases).