Oesophagostomum spp (nodular worms) are prevalent worldwide; O dentatum is the most common species, whereas O quadrispinulatum appears to be slightly more pathogenic. The adults are found in the lumen of the large intestine. They are 8–15 mm long, slender, and white or gray. The life cycle is direct. Eggs are passed in the feces; infective third-stage larvae (L3) are found on pasture within 1 week and can survive for approximately 1 year under optimal conditions. Infection results from ingestion of L3, which penetrate the mucosa of the large intestine within a few hours after ingestion and return to the lumen in 6–20 days. The prepatent period is approximately 3–6 weeks. A periparturient rise in worm egg output has been observed in sows from 2 weeks before parturition to weaning; however, this phenomenon is far less constant in pigs than sheep and its epidemiological importance is questionable. Adults cause little damage to the mucosa so clinical signs tend to be absent. Heavily infected pigs may have anorexia, emaciation, and gastrointestinal disturbances. Death seldom occurs.
The serosa shows small nodules, their size reflecting species and previous exposure. In severe cases, the intestinal wall may be thickened and necrotic. Heavy infections may decrease the lactation capacity of sows and the body weight of growing pigs.
Infection induces only moderate immunity; hence, prevalence of nodular worms tends to be higher in the older age groups (sows, boars). In patent infections, typical strongyle eggs (66–80 × 38–47 mcm) are found in feces, often in large numbers. These can be differentiated from those of Hyostrongylus by larval culture.
At postmortem examination, the worms and lesions are readily visible. The benzimidazoles, levamisole, piperazines, dichlorvos, pyrantel tartrate, doramectin, and ivermectin are effective; however, anthelmintic resistance has been observed for benzimidazoles and pyrantel. A diet composed of highly degradable carbohydrates may support worm control by creating unfavorable conditions, which decrease worm establishment and fecundity.