Trichurissuis (Whipworm) in Pigs

Trichuris suis (whipworm) is one of the most common nematodes found in pigs worldwide. The adult worms are 5–6 cm long and whip-shaped. The slender cranial portion embeds within the epithelial cells of the large intestine, especially the cecum, with the thickened caudal third lying free in the lumen.

Trichuris suis egg

Image

Trichuris suis egg recovered by fecal sedimentation, 63 × 30 mcm. Eggs are symmetrical, have a smooth shell, and are bipolar plugged. 400X total magnification.

Courtesy of Dr. Trey Tomlinson.

Infection with whipworm is by ingestion of eggs containing an infective first-stage larva. The larva hatches and penetrates the distal ileal, cecal, or colonic mucosa. The nematodes complete four molts, after which the caudal end begins to protrude into the lumen. The prepatent period is 6–7 weeks; longevity is 4–5 months (1). Infection is generally light, with no clinical signs. Heavy infections can cause inflammatory lesions in the cecum and adjacent large intestine and can be accompanied by diarrhea and unthriftiness.

Capillarid egg

Image

Capillarid egg recovered by fecal sedimentation. Eggs are similar to Trichuris suis; however, they are asymmetrical and have rough shells. They are bipolar plugged; however, they are often smaller than T suis eggs. 400X total magnification.

Courtesy of Dr. Trey Tomlinson.

Clinical signs of whipworms most often occur in young animals; resistance is both acquired and age-related. The eggs are symmetrical, double-operculated, brown, 50–68 × 21–35 mcm, with a smooth shell and single cell (see Trichuris suis egg image). These must be differentiated from capillarid eggs, which are typically smaller bipolar plugged eggs that are asymmetrical with a rough shell (see Capillarid egg image). The Trichuris larva develops within the egg in approximately 3 weeks (2). Eggs are heavy; thus, a good fecal flotation technique with media of proper specific gravity is essential.

Trichurid females lay eggs sporadically, and this, along with egg density, means that false-negative fecal tests are common. Clinical trichuriasis is usually associated with the larval stages, and diarrhea is common in young pigs (2). Additionally, mucosal ulceration, edema, and hemorrhage are often associated with heavier infections (1). In prepatent infections, examination of mucosal scrapings taken at postmortem examination for larval stages of the parasite is recommended. Mature parasites are easily found after ingesta is washed away and can be identified by their size and "whiplike" form.

Careful evaluation of product labels is important, as not all anthelmintics have good activity against T suis. Dichlorvos, some benzimidazoles, and doramectin are effective against the adult worms (1, 3).

Biologically, whipworm eggs are comparable to Ascaris eggs—they are highly resistant to chemicals and can remain infective for up to 11 years (4, 5). Controlrelies on thorough cleaning of the affected area and moving the animals to clean plots. If animals are indoors, using slatted floors rather than dirt or soft floor will help minimize transmission (2). Tillage of pastures between uses can decrease the number of eggs that survive.

Trichuris eggs develop rather slowly (10–12 weeks under optimal conditions) (2), and because they do not develop at temperatures < 16°C (60.8°F), there is only one generation per year in temperate geographic areas.