Oesophagostomum spp (Nodular Worm) in Pigs

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 cecum and colon. They are 8–15 mm long, slender, and white or gray.

The life cycle of nodular worms 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. Larvae are susceptible to persistent freezing and hot, dry seasons (1).

Nodular worm infection results from ingestion of L3, which penetrate the mucosa of the ileum, cecum, and colon within a few hours after ingestion and return to the lumen in 6–20 days. The prepatent period is approximately 3–6 weeks (2, 3). Heavily infected pigs can have anorexia, emaciation, and GI disturbance. Death seldom occurs.

Adult nodular worms rarely cause disease. Nodules form in the intestinal mucosa from developing larvae, their size reflecting species and previous exposure. Nodules can be 2 mm or larger in some infected pigs (2). In severe cases, the intestinal wall can be thickened and necrotic. Heavy infections can decrease the lactation capacity of sows and the body weight of growing pigs (2, 3).

Nodular worm 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-type eggs (see Strongylid egg image) (66–80 × 38–47 mcm) are found in feces, often in large numbers. The eggs cannot be reliably differentiated from those of Hyostrongylus rubidus, the red stomach worm, or Globocephalus urosubulatus, the pig hookworm (however, Globocephalus eggs are often smaller), so species differentiation should be made by larval culture. At postmortem examination, nodular worms and lesions are readily visible.

Strongylid egg

Image

Strongyle-type eggs recovered by fecal flotation, 67 × 39 mcm. Eggs of Oesophagostomum, Hyostrongylus and Globocephalus are morphologically similar. 630X total magnification.

Courtesy of Dr. Heather Walden.

Treatment of nodular worms with benzimidazoles, levamisole, piperazines, dichlorvos, pyrantel tartrate, doramectin, or ivermectin is effective; however, anthelmintic resistance has been observed for benzimidazoles, levamisole, ivermectin, and pyrantel (4, 5, 6). This resistance is low in frequency; however, it does highlight the need for thoughtful use of anthelmintics and appropriate management practices.

Studies have shown that diet can influence Oesophagostomum survival and infection in the host. A diet composed of highly degradable carbohydrates can create unfavorable conditions for worm establishment and fecundity (3, 7).