Hydatids is a disease that can affect humans, sheep and other animals, and is contracted from dogs. If the hydatid tapeworm is present in a dog's intestine, tapeworm ova are passed out in the faeces and may be ingested by humans or other animals. The ova develop large cysts in the organs, as shown here in the liver of an infected sheep (top), and can cause severe illness or death. After an intensive hydatids control programme, New Zealand was declared free of the disease in 1999.