National Geographic : 2007 Oct
Long-term survival is only one form of evolu tionary success. Gross abundance and broad dis tribution is another. Think of tortoises and rats. Tortoises tend to live by a conservative strategy, remaining with in their preferred habitat and reproducing slowly. Rats tend to be opportunists, fanning out, traveling across land and sea as stowaways, arriving in new places and reproducing fast. Sim ilarly, pathogens may differ in their degree of adventurousness. Spillover from a reservoir host isn't necessarily an accident, always leading to the dead end. It may be a strategy, leading to evo lutionary success. Simian immunodeficiency virus (SIV) achieved that sort of success when it spilled over from one subspecies of chim panzee into humans, probably in west-central Africa, and became HIV-1. Close contact between humans and other spe cies can occur in various ways: through killing and eating of wild animals (as in Mayibout II), through caregiving to domestic animals (as in Hendra), through fondling of pets (as with monkeypox, brought into the American pet trade by way of imported African rodents), through taming enticements (feeding bananas to the monkeys at a Balinese temple), through intensive animal husbandry combined with habitat destruction (as on Malaysian pig farms), and through any other sort of disruptive pene tration of humans into wild landscape-of which, needless to say, there's plenty happen ing around the world. Once the contact has occurred and the pathogen has crossed over, two other factors contribute to the possibility of cataclysmic consequences: the sheer abundance of humans on Earth, all available for infection, and the speed of our travel from one place to another. When a bad new disease catches hold, one that manages to be transmissible from per son to person by a handshake, a kiss, or a sneeze, it might easily circle the world and kill millions of people before medical science can find a way to control it. But our safety, our health, isn't the only issue. Another thing worth remembering is that disease can go both ways: from humans to oth er species as well as from them to us. Measles, polio, scabies, influenza, tuberculosis, and oth er human diseases are considered threats to non human primates. The label for those infections is anthropozoonotic. Any of them might be 102 NATIONAL GEOGRAPHIC * OCTOBER 2007 DANGEROUS FOOD A butchered monkey at a market in the DemocraticRepublic of the Congo has been partially cooked. Such bush meat is the only source of animalprotein in some impoverishedparts of sub-SaharanAfrica. If this monkey-or any of the many animals these women handle in a communal butchering area on a typical day carrieda zoonotic disease, many people would be exposed.