Ed Yong in The Atlantic:
The Congo is one of the most biodiverse countries in the world. It was here that HIV bubbled into a pandemic, eventually detected half a world away, in California. It was here that monkeypox was first documented in people. The country has seen outbreaks of Marburg virus, Crimean-Congo hemorrhagic fever, chikungunya virus, yellow fever. These are all zoonotic diseases, which originate in animals and spill over into humans. Wherever people push into wildlife-rich habitats, the potential for such spillover is high. Sub-Saharan Africa’s population will more than double during the next three decades, and urban centers will extend farther into wilderness, bringing large groups of immunologically naive people into contact with the pathogens that skulk in animal reservoirs—Lassa fever from rats, monkeypox from primates and rodents, Ebola from God-knows-what in who-knows-where.
On average, in one corner of the world or another, a new infectious disease has emerged every year for the past 30 years: mers, Nipah, Hendra, and many more. Researchers estimate that birds and mammals harbor anywhere from 631,000 to 827,000 unknown viruses that could potentially leap into humans. Valiant efforts are under way to identify them all, and scan for them in places like poultry farms and bushmeat markets, where animals and people are most likely to encounter each other. Still, we likely won’t ever be able to predict which will spill over next; even long-known viruses like Zika, which was discovered in 1947, can suddenly develop into unforeseen epidemics.