The large roundworms (ascaroid nematodes) of dogs and cats are commonly encountered, especially in puppies and kittens. Of the three species, Toxocara canis, T leonina, and T cati, the most important is T canis, not only because its larvae may migrate in man, but because fatal infections may occur in young pups. T leonina occurs most often in adult dogs, less often in cats. Distribution of T cati, the feline roundworm, varies around the world. In domestic animals, infective eggs may ingested directly from other animals or their faeces, or through eating infected animals (such as rats). Toxocara species also occur in wild carnivores who are probably infected by eating other infected animals.