The plague has never died out in the world. And neither have rats. In some countries, they are a big pest. Not just undeveloped countries either. In 1995 Britain found that it had 60 million rats. That meant more rats than people there. In London alone, 300,000 properties were infested with rats. The increase was blamed on the rats' resistance to poison, the milder weather and the growing fast-food industry with its throw-away rubbish. Scientists warned that the rats were a threat to people because they could spread disease.
