In the eyes of dog lovers, the dog is man's best friend. But for much wildlife, loose dogs may be a dangerous enemy, according to a study by a biologist from Utah State University in the US. Based on much existing research and their own case studies, Julie Young of Utah State University and four other scientists conclude that loose dogs may represent a huge danger to wildlife, especially endangered species, by hunting down or worrying them and by spreading diseases. They also found that dogs, their worldwide numbers around 500 million, can cause more damage to wildlife and livestock  than wolves and other enemies of these animals. Young gave examples from the US state of Idaho, where research showed the presence of dogs reducing some deer populations. On the Navajo American Indians' reservation in northeastern Arizona, packs of loose dogs are chasing livestock. They have killed populations of small animals such as rabbits and act as a disease carrier for rabies  among people and other animals, she said. Loose dogs also were to blame for distemper outbreak leading to a die-off of endangered black-footed ferrets in northwestern Wyoming in the 1980s. The phenomenon is not just limited to US; it's a global problen. Julie Young once studied three endangered species in central Asia: wild sheep, gazelles and antelope. The rate of injury and death to these animals by loose dogs was very high. In another case, Young found that dogs, not wolves, as originally suspected, were responsible for a large number of livestock killings in the mountainous Basque country between Spain and France. Authors of the new study said the problem is likely to worsen as communities expand. Then how to deal with it? Indeed, in many countries, leash  laws permit punishment of dog owners whose pets chase wildlife. But lawbreakers are rarely punished because the police lack both people and money. Young has low-cost solutions to the problem for dog lovers, though. They include public dog-training programs and vaccinating   dogs against rabies and other illnesses. . Which of the following statements about loose dogs is TRUE according to the research?
There are around 500 million loose dogs around the world. The black-footed ferrets in northwestern Wyoming were once the main food source of local loose dogs. The problem caused by loose dogs is the most serious in the US. People used to think that wolves, rather than loose dogs killed livestock in the Basque  country.