Asked by: Richard O’Neill, Glasgow
Animals are a notorious source of infections in humans. The Spanish Flu Pandemic, which killed over 20 million people between 1918 and 1920, is believed by many researchers to have had its origins in a virus carried by birds. But humans are also capable of passing on deadly viruses and bacteria to animals, in a phenomenon known as reverse zoonosis.
Some serious human diseases cause relatively mild health problems in other animals. For example, diphtheria – which is potentially fatal in humans – causes nothing more than ulcers on cattle. But other human infections, such as hepatitis and influenza, remain just as deadly if transmitted to animals via contact with humans in farms, zoos or veterinary surgeries. There have even been cases of tuberculosis claiming the lives of circus elephants following infection from humans.