Which of the following vaccines is classified as a core vaccine for dogs?

The vaccine classified as a core vaccine for dogs is Distemper. Core vaccines are those that are considered essential for all dogs due to the severity of the diseases they prevent, their widespread occurrence, and the high risk of exposure. Canine distemper is a highly contagious viral disease that affects multiple body systems, including the respiratory, gastrointestinal, and nervous systems. It can lead to severe illness and is often fatal.

Considering the other options, Leptospira, Bordetella, and Lyme disease vaccinations are typically classified as non-core vaccines. While they are important in certain circumstances—especially based on the dog's lifestyle, geographic location, and exposure risks—they do not carry the same universal necessity as the core vaccines such as Distemper, Parvovirus, and Adenovirus. Therefore, Distemper stands out as a core vaccine that is strongly recommended for all dogs to protect against a serious and potentially deadly disease.