We are used to the idea that many diseases pass to us from other creatures – such as swine flu and bird flu in recent years, while, of course, the deadliest epidemic in history, bubonic plague, came from the flea of the black rat.
Now there is a new one to worry about – Congo fever, which has afflicted Africa and the Middle East for a long time, but has now started killing people in Gujarat in north-western India. It is caused by a virus transmitted by ticks that feed on a variety of wild and domestic animals and birds, and the death rate of those infected is about one in three.
It is reckoned that about three quarters of all new diseases pass to humans from animals, and the growing prosperity of countries such as India could make things worse. As people get richer they tend to eat more meat, and that means that those who once had just a few chickens in their backyards are now keeping animals, sometimes in quite large numbers.
The International Livestock Research Institute reckons that the world has 450 million smallholders, and as towns grow bigger, more animals and meat are transported, helping infections to spread further and faster.