Ascaris suum, also known as the large roundworm of pig, is a parasitic nematode that causes ascariasis in pigs. While roundworms in pigs and humans are today considered as two species (A. suum and A. lumbricoides) with different hosts, cross-infection between humans and pigs is possible; some researchers have thus argued they are the same species. Ascariasis is associated with contact to pigs and pig manure in Denmark. A. suum is distributed worldwide and grows up to in length. Ascaris infections are treated with ascaricides. A. suum is in the family Ascarididae, and is one of the oldest associations to mankind. Life cycle Pigs get infected with A. suum by ingesting infectious parasite eggs that are present in the environment. The larvae of Ascaris complete two moults within the egg; therefore, the larvae emerging from the egg is not a second-stage larva (L2) as was previously presumed, but rather a third stage larva (L3) covered by a loosened L2 cuticle. The larvae hatch from the egg inside the pig's intestines and subsequently start their migration through the body. First, they penetrate the intestinal wall at caecum/colon and use the mesenterial blood veins to migrate to the liver. After burrowing their way through the liver tissue, they again use the efferent blood stream to carry them to the lungs. There, they get stuck in the capillaries surrounding the lungs and they penetrate the lung alveoli. It takes approximately 7 days to reach the lungs. Once the larvae are inside the lung, they migrate up the respiratory tree and are eventually coughed up and swallowed by the host to reach the small intestine again as soon as 10 days after infection. There, the larvae undergo their first molt inside the host to reach the L4 stage by day 14 post-infection. Around day 25 post infection, they develop into the L5 stage. Worms reach adulthood 6 weeks after infection, and when both female and male worms are present in the same host, fertilized eggs are produced and secreted by the female worm. These eggs are then excreted together with the faeces. After an incubation period, infective stage larvae develop in the eggs and are ready to cause infection in a new host. Paratenic hosts ingest the eggs and the L3 larvae remain in the tissues of the paratenic host until a pig eats them. These may include beetles and earthworms, as well as