Robert Rayford

Frozen samples were eventually tested and came back positive for a rarer branch of the virus, Group O, which is a detail worth remembering because it points somewhere specific on a map.

And in St Louis in 1969, a teenager named Robert Rayford died after a long decline that baffled everyone who examined him.

swelling, infections that would not resolve, unusual lesions, an immune system that had simply given up.

His doctors were so genuinely confused that they preserved tissue samples, which was not a routine act and was, in retrospect, an enormous gift.