THE MERCK VETERINARY MANUAL
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Stomach Worms in Pigs

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Three types of stomach worms are seen in pigs: a thin worm, Hyostrongylus rubidus (the red stomach worm), and 2 thick stomach worms, Ascarops strongylina and Physocephalus sexalatus. H rubidus is ∼6 mm long and slender and has a direct life cycle. The thick stomach worms are 10–20 mm long and much stouter and have coprophagous beetles as intermediate hosts. All 3 stomach worms are found worldwide but mainly in outdoor pigs.

When present in large numbers or when the host's condition is reduced by poor nutrition or other factors, these worms may cause variable appetite, anemia, diarrhea, or weight loss, and may contribute to a thin sow syndrome. H rubidus characteristically is found under a heavy catarrhal or mucous exudate and may produce mucosal lesions similar to those of Ostertagia spp in ruminants, except that hemorrhages are more common. Retarded development of larval stages in the mucosa is analogous to that of Ostertagia. In sows, inhibited larvae may resume development near parturition and may cause severe gastritis and, in addition, contaminate the environment of the young pigs. Egg excretion per female Hyostrongylus worm is generally very low compared with that of other nematode genera.

Clinical signs other than unthriftiness are not obvious. Fecal examinations may show the distinctive ova of Physocephalus and Ascarops—small (35–40 × 17–20 mm), thick-shelled eggs containing active larvae. Hyostrongylus ova resemble those of other strongyle worms (eg, Oesophagostomum), and fecal cultures are required to obtain infective larvae for differential diagnosis.

At necropsy, adult worms, especially Physocephalus and Ascarops, are readily seen. Mucosal scrapings for microscopic examination are essential for detection of immature Hyostrongylus.

The newer benzimidazoles, probenzimidazoles, and ivermectin are highly effective against adult and immature stages (including hypobiotic larvae) of Hyostrongylus. Ivermectin has activity against adult Ascarops.

Last full review/revision March 2012 by Allan Roepstorff, DSc, PhD, MSc

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