Roundworms are white, round-bodied worms, and can get up to 18cm long! These worms spend most of their life within the gut of dogs, feeding on intestinal contents.
Roundworms reproduce by laying eggs within the intestine. These eggs are passed out with faeces, mature for up to seven weeks, and then become infectious. Dogs then ingest these infectious eggs, which hatch into larvae. Importantly, larval roundworms can travel out of the gut to a wider range of tissues, including multiple organs such as the liver and lungs, skeletal muscle and the gut wall, where they may form cysts. This allows dogs to maintain a level of infection, and bitches can pass on infections to their puppies via the placenta or milk. This infection of puppies is the most common route of infection.
Sadly, toxocara can also infect humans and, while usually harmless in adults, can cause serious damage to children’s eyesight.