The common roundworm of pigs, also called Ascaris suum, infects millions of pigs worldwide. Here you can find more detailed information about the curious life cycle of this parasite and it's prevalence. Life Cycle - Pigs get infected by ingestion of parasite eggs present in the environment (Fig 1A). After reaching the intestine, the larva is released in the lumen of the inestine of its host (Fig 1B). - The larva migrates through the intestinal tissue and use the bloodstream to get to the liver (Fig 1D). - After about 1 week, the migrating larva reaches the lungs (Fig 1D), where it penetrates the alveoli and moves up the respiratory tree and eventually gets swallowed again. The larva settles itself in the small intestine (Fig 1E) and has the opportunity to develop into an adult parasite. - About 6 weeks after initial infection the shedding of freshly fertilized eggs by the adult worms begins, hereby completing the life-cycle (Fig 1F). Figure 1: Representation of the life cycle of Ascaris suum. Link to a PDF of the detailed Life cycle of A. suum. Prevalence Ascaris suum infections are presumed to be present in pigs all over the world. Although few countries hold up-to-date information on its prevalence, several studies show that this parasite remains highly present on pig farms. Table 1: Overview of a number of studies reporting the prevalence of Ascaris suum in pigs either by detection on farm level or on pig level by using either EPG, the number of affected livers or an experimental serodiagnostic test for the diagnosis of the disease. Link to a PDF of Table 1 with detailed references. There are three major reasons why Ascaris is still so prevalent on high intensity pig farms: 1) Because of the direct life cycle, this parasite is not dependent on the presence of an intermediate host for the completion of its life cycle. 2) The extremely high fecundity of the parasite (>200,000 eggs/day/worm) cause a heavy contamination of the environment. 3) Ascaris eggs are extremely resistant and can remain infective for years. A hard eggshell protects the embryo during its time in the environment (see Fig. 3). Figure 2: Two embryonated A. suum eggs and 1 unfertilized egg. Ascaris suum
