Animals used by laboratories for testing purposes are largely supplied by dealers who specialize in selling them to universities, medical and veterinary schools, and companies that provide contract animal-testing services. It is comparatively rare that animals are procured from sources other than specialized dealers, as this poses the threat of introducing disease into a colony and confounding any data collected. However, suppliers of laboratory animals may include breeders who supply purpose-bred animals, businesses that trade in wild animals, and dealers who supply animals sourced from pounds, auctions, and newspaper ads. Animal shelters may also supply the laboratories directly. Some animal dealers, termed Class B dealers, have been reported to engage in kidnapping pets from residences