In Philip Curtin's Image of Africa he talks about the image of Africa as the "White Man's Grave." For the late 18th and early 19th century British, the "Africa" here usually meant the West African coast--namely, places such as Sierra Leone. English soldiers stationed at coastal outposts had very high death rates. While some of this was due to hostility of locals (traders, primarily, who could 'rethink' their toleration of the tiny British contingents at any time), it was the death rates from diseases like Malaria that were truly shocking. Curtain estimates that a posting in West Africa around the 1830s had almost a 50% death rate for enlisted men. (and half that for officers). (the more temperate Cape Colony had fewer malaria problems, and so seems to have sometimes escaped the "white man's grave" reputation...) Missionaries had similarly astronomically-high death rates from disease (though, I think, lower than barracked soldiers, because many missionaries were in African communities and could thereby benefit from local treatments, while the soldiers suffered under myopic and inadequate European medicine.)

In his book Tools of Empire (a good read) Daniel Headrick similarly argued that West Africa was an incredibly lethal posting, but that this was all made moot by the introduction of quinine after the 1850s. (Headrick's "tools" of empire are quinine, the steamboat, and the repeating rifle). This argument about quinine is oft-repeated.

But I'm very wary of Headrick's argument about malaria, though. In an error all-too typical of historians of technology, he tends to emphasize the dates that the technology (in this case quinine) was first discovered or introduced, rather than the dates that its usage became actually widespread enough to be significant. When you get to when quinine was a standard prophylaxis for Europeans stationed in West Africa, we're already well into the new imperialism of the 1880s... (as the dates in Headrick's own footnotes show). So Headrick's argument that this was a precondition for conquest just always seemed off to me.

Much more has been written about disease in Africa in recent years, but I'm not necessarily caught up enough on that research to rattle it off from memory.

Still, the long-story made short of all this is: The West African coast in the 1830s or 40s had to be a brutal posting for a soldier. Possibly the worst. Because you had an even chance of not making it back to merry old England.