Porcine proliferative enteropathy is a common diarrheal disease of growing-finishing pigs and young breeding pigs, characterized by hyperplasia and inflammation of the jejunum, ileum, cecum, and colon. Disease can be subclinical or mild and self-limiting; in some instances, however, there is persistent diarrhea, severe necrotic enteritis, or hemorrhagic enteritis with high mortality.
The etiology of porcine proliferative enteropathy is Lawsonia intracellularis, an intracellular, gram-negative, small rod-shaped bacterium. The organism has been cultivated only in cell cultures, and attempts to propagate it in cell-free medium have failed. In infected pigs, the bacteria can be visualized in the apical cytoplasm of proliferative enterocytes. Bacterial replication occurs freely in the cytoplasm of enterocytes, and some of these bacteria pass to each daughter cell during mitosis. Infected cells fail to mature and continue to replicate, resulting in a proliferative enteropathy. Most pigs will eventually recover from infection, and cellular immunity is likely important for disease resolution.
The more common, nonhemorrhagic form of porcine proliferative enteropathy often affects pigs weighing 40–80 lb (18–36 kg) and is characterized by sudden onset of diarrhea. The feces are loose to watery and often reddish brown or faintly blood tinged. Most affected pigs recover spontaneously; however, a noteworthy number may develop chronic necrotic enteritis with progressive loss of body condition. The hemorrhagic form is characterized by cutaneous pallor, weakness, and melena, and affected animals may die unexpectedly. Pregnant gilts may abort.
Lesions may occur anywhere from mid-jejunum into the cecum and colon; however, they are often most obvious in the ileum. The wall of the intestine is thickened, the mesentery may be edematous, and the mesenteric lymph nodes are frequently enlarged. The intestinal mucosa appears thickened and rugose, may be covered with a brownish or yellow fibrinonecrotic membrane, and often has surface hemorrhages. Yellow casts of necrotic material may be found in the ileum or passing through the colon. Circumferential mucosal necrosis in chronic cases causes the intestine to be rigid, resembling a garden hose. Proliferative mucosal lesions are often present in the colon; however, they can be multifocal and detected only by careful inspection at postmortem examination. In the profuse hemorrhagic form, reddish black or tarry feces are present in the colon, and there is often a characteristic accumulation of clotted blood in the ileal lumen.
Confirmation of porcine proliferative enteropathy is based on histologic observation of characteristic proliferation of mucosal crypts. L intracellularis (small, curved rods resembling Campylobacter) can usually be demonstrated by silver stains or immunohistochemistry. PCR assays are available and are useful for confirmation of the presence of L intracellularis nucleic acid. PCR assays can be applied to feces or population-level samples such as oral fluids; however, the organism is endemic in most swine herds and, thus, detection alone may be of little diagnostic value. Bacterial culture of intestine and lymph nodes to exclude Salmonella infection, together with histologic examination and culture of cecum and colon to exclude swine dysentery, is an essential additional procedure because mixed infections with these agents are common. Serologic assays are available; however, they are of limited use in disease diagnosis, given the endemic nature of this agent, and are more suited for surveillance and monitoring at a herd level.
To treat porcine proliferative enteropathy, various antimicrobials can be administered parenterally to acutely affected pigs, and by feed or water to the remainder of the group. Antimicrobial therapy can help reduce disease severity and prevent development of chronic, irreversible, necrotic enteritis. Commercial vaccines are available and can be highly effective in mitigating disease.
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Vannucci FA, et al. Proliferative enteropathy. In: Zimmerman JJ, et al, eds. Diseases of Swine, 11th ed. John Wiley and Sons, Inc; 2019: 898–911., Hoboken, NJ.