The thing about Africa, why it’s got so many parasites and viruses and bacterial diseases and crazy deadly animals is that that’s where humans evolved, and that’s where proto-humans evolved, and that’s where the primates that proto-humans came from evolved, which means that the stuff there is co-evolved with humans. It survived ages and ages of contact with humans, a good deal of things there recognize humans as predators and have anti-human defenses, or worse yet recognize them as prey.

Like, as soon as humans got to the Americas they killed the megafauna. Wooly mammoths? They just ganged up on them with spears. African Elephants? You try to gang up on an elephant with spears, they will fuck you up. You just look shifty around a wild elephant, they will fuck you up. Elephants will fuck you up for the hell of it. Gunpowder finally tipped the balance in our favor.

American bison? As soon as guns were introduced to their environment they went from abundant as hell to nearly extinct. You would just walk up to a herd and pick them off one by one and they would be all “huh”? You ever heard of the Big 5, the classic safari set of all-time badass animals to hunt? Lion, elephant, rhino, leopard, buffalo. You know which one kills the most hunters? The buffalo. Because if one of those fuckers sees you get close it will immediately charge at you full speed to gore you.

The American alligator? Rednecks will wrestle those things for fun. The Nile crocodile? Count human children as favored prey.

Australia’s a bit different, everything’s deadly there because it’s so resource-poor, in water and minerals, so it’s heavily selected for incredibly efficient killers. One of the most efficient ways to kill, in terms of resource expenditure, is poison, which is why so many desert animals are poisonous, which is why everything in Australia is poisonous.

That’s why governments and meta-governments try to maintain such a strong taboo against chemical weapons, not so much that it’s a particularly horrible way to kill but because it’s such an efficient way to kill - anyone with access to 1880s-level technology can perform AoE attacks with a huge radius and near-100% lethality - and they’re trying to keep human power struggles from turning into Australia.