Prevalence and molecular epidemiology of enterotoxigenic Escherichia coli in diarrhoeic neonatal and post-weaning piglets in Gauteng and North West Provinces South Africa

Abstract

Enterotoxigenic Escherichia coli (ETEC) is a major cause of pig diarrhea in piglets and weaners. The main virulence factors of ETEC are fimbrial adhesins and enterotoxins. Fimbrial adhesins including F4 (K88), F5 (K99), F6 (987P), F18 and F41 mediate attachment to enterocytes which results in colonization of the intestinal microvilli. Furthermore, two afimbrial adhesins have been identified in ETEC isolates from diarrheic pig: adhesin involved in diffuse adherence (AIDA-1) and porcine attaching and effacing-associated factor (Paa). ETEC produce two enterotoxin variants: the heat stable (STa, STb, EAST1) and heat labile (LT) which activate enterocytes to secrete fluid and electrolytes. ETEC can also produce a Shiga-toxin (Stx2e) which has been associated with edema disease in piglets. To determine the prevalence and risk factors associated with ETEC-induced diarrhea in piglets in Gauteng and Northwest Provinces of South Africa, 228 rectal swabs from randomly selected diarrheic and non-diarrheic pigs were collected from 8 piggeries of different sizes (16 to 650 sow units) in two provinces of South Africa and 22 piglet samples which were collected from unidentified farms across South Africa were received from pig practitioners. Isolates that were cultured from pig swabs were screened for four ETEC toxin genes (STaP, STb, LTb and Stx2e) by multiplex polymerase chain reaction (mPCR). To identify ETEC, one hundred and thirty-one toxinpositive isolates were further tested for virulence genes including F4 (K88), F5 (K99), F6 (987P), F18 and F41 fimbriae, non-fimbrial adhesins Paa, AIDA-1, the enteroaggregative heat-stable (EAST1) enterotoxin, and for serogroups O9, O139, O141, O149 by PCR. A number of pig management related variables identifying ETEC risk factors were considered using a checklist. For risk factor analysis, laboratory results were matched with 7 animal and 17 management-related variables and data were analyzed using univariable and multivariable logistic regression.