(Science) fiction: virus / disease outbreak in a jungle-like environment

[Veronika]

Hi,
I'm searching for a book I came across in a public library in 2005-ish. It was a Czech translation but I believe the original may have been in English. Genre most likely science fiction, adult literature. No idea as to the title or author.

--possible spoilers below--

Plot-wise, I believe the main story took place in a jungle or remote jungle-like country. A scientist was sent to either investigate a virus outbreak - or may have been conducting research which caused it. The virus / disease was super contagious and, from memory, resulted in some nasty physiological changes in the human body, always fatal within a very short time-frame.
Two children - possibly siblings - may (or may not) have been central to the plot as I seem to recall only the two of them were unaffected and turned out to be the (anti)virus carriers.
The only other thing I remember is that one chapter started with a brothel scene, briefly describing the tail-end of one of the encounters typical for such establishment. This was to hint at the cause of the rapid spread of the disease (exchange of bodily fluids).

Any ideas, please do let me know. Thank you.