Which parasite in dogs is most commonly associated with visceral larva migrans in children?

Toxocara spp. is the correct choice because these roundworms are known to cause visceral larva migrans in humans, particularly in children. The lifecycle of Toxocara involves dogs and other canines as definitive hosts. When children accidentally ingest Toxocara eggs from contaminated soil or surfaces, the larvae can migrate through the body, leading to various health issues, including visceral larva migrans. This condition is characterized by the migration of the larvae through tissues, causing inflammation and damage, particularly affecting organs such as the liver and lungs.

The other parasites listed, while they may affect dogs, do not typically lead to visceral larva migrans in humans. Ancylostoma species (hookworms), for example, primarily cause cutaneous larva migrans when larvae penetrate the skin but do not usually cause visceral disease. Dipylidium species (the flea tapeworm) and Taenia species (another type of tapeworm) also do not have the same capability to cause visceral larva migrans, as their transmission and pathology routes differ significantly from those of Toxocara. Hence, Toxocara remains the primary concern in the context of visceral larva migrans in children.