SOLVED. Adult Horror. Set in Africa probably, explorer experiences inexplicable phenomena on his body. Read in the 70's. [s]

[Luisa]

It was a novel, not very long. Very disturbing. An explorer, I think, starts having some sort of ulcers on his body. Those ulcers start to grow, until out of them little heads start erupting. The man cut the heads, but in the end one fully formed tiny warrior comes out. He ist extremely ferocious, impossibly fast, and dead set to kill the other. I think he succeeded, but I'm not sure. Maybe there was an event beforehand that prompted and explained this as a sort of vendetta, but I don't remember. I read it when I was around 16 and it haunted me for a while, until I forgot title and author but not the horror.
Thank you in advance

[Kris]

Luisa, would you call this a horror novel?

[Luisa]

Yes, judging from the effects it had on me, it was definitely a horror story.

[Luisa]

Yes! You got it on the first try! Thank you so much!

[Luisa]

I just reread it on Project Gutenberg. Now I am perplexed again: where did I get the notion that the pygmy came out and pursued Stone? Did I mix two stories? The impossibility of squashing so tiny an assassin was part of the horror...