Category D includes the biology of vertebrate animals (animals with backbones) and that are associated with public health problems in some way, especially in connection with infectious diseases of people. Domestic and wild rodents fall under this category, with special emphasis on domestic rats and mice, and wild rodents that are associated with hantavirus infections of humans. Other such animals of concern include possums, skunks, squirrels, and poisonous snakes. Methods of control of some of these animals is included, most frequently those animals such as Norway rats and house mice that are closely associated with human habitats.