What cause the dog to roam around the neighborhood in to kill a mockingbird?

In "To Kill a Mockingbird," the dog roaming the neighborhood is described as a "mad dog" infected with rabies. It poses a threat to the community, prompting Atticus Finch to take action by shooting it to protect the residents. The incident serves as a metaphor for the underlying racism and prejudice in the town that needs to be confronted and eliminated.