Edema disease as the cause of neurologic signs in nursery pigs
Josepha DeLay, Đurđa Slavić, Clint Lichty
Animal Health Laboratory, University of Guelph, ON (DeLay, Slavić); South West Ontario Veterinary Services, Stratford, ON (Lichty)
AHL Newsletter 2019;23(4):10.
An acute episode of diarrhea and neurologic deficits involved 25% of nursery pigs in a 1200 head herd. Post-weaning colibacillosis and bacterial meningitis due to Streptococcus suis were the main clinical differential diagnoses. Field postmortems were conducted on 2 euthanized pigs and samples were forwarded to the Animal Health Laboratory for evaluation.
Colibacillosis was confirmed in both pigs based on histologic evidence of adherent bacilli at the luminal surface of enterocytes lining small intestinal villi, and isolation of Escherichia coli from feces of both pigs. Both pigs also had variably severe atrophic enteritis suggestive of concurrent viral enteritis due to porcine rotaviruses or coronaviruses (no further testing pursued for confirmation). Typical lesions of bacterial meningitis were not present, however focal edema was identified histologically in brainstem white matter of 1 pig. Genotyping of fecal E.coli isolates confirmed the presence of F18 and stx2e toxin genes, compatible with the profile for the subset of E.coli responsible for edema disease in swine. F4/K88, F5/K99, and F41 fimbrial genes of other enterotoxigenic E.coli strains were not identified in the isolates, and F4/K88 and F5/K99 antigens were not detected by agglutination serotyping.
In this case, both diarrhea and cerebral edema leading to neurologic disease were attributed to F18 Stx2e-positive E.coli. Stx2e toxin is produced by E.coli in intestine and is absorbed into the systemic circulation. The toxin acts at sites distant from intestine, targeting and injuring blood vessels in various organs causing edema. Although clinical disease is dramatic, with a rapid and fatal course, gross and histologic lesions may be subtle.
Edema disease is rare, but is an important differential diagnosis for neurologic disease in nursery and early grower pigs. To date, 4 cases of edema disease have been diagnosed at the AHL in 2019. The diagnosis relies on identifying compatible gross and histologic lesions, in conjunction with culture of F18, Stx2e-positive E.coli from intestine. Palpebral and gastric mural edema may be seen grossly. Diarrhea is often absent, and histologic evidence of intestinal colonization by the bacteria is uncommon. As a result, intestine is often not included for culture in pigs with neurologic signs, and the correct diagnosis can be missed.
Fairbrother JM and Nadeau, E. Colibacillosis in Diseases of Swine, 2019. JJ Zimmerman, LA Karriker, A Ramirez, KJ Schwartz, GW Stevenson, J Zhang, ed. p807-834.