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Escherichia Coli infection --- Enterohemorhagic Escherichia Coli --- Entero pathogenic Escherichia Coli --- veterinary --- genetics

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Chickens --- Escherichia coli infections in animals --- Diseases

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Water --- Escherichia coli --- Bacterial pollution of water --- Feces --- Pollution

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At the weaning period, piglets are exposed to a series of stressors and become more susceptible to many diseases. Edema disease (ED) mainly occurs shortly after weaning. It is highly fatal with mortality up to 90% in infected pigs and is considered as a source of economic loss for pig industry worldwide. ED is caused by Stx2e-producing Escherichia coli (STEC), producing the F18 fimbrial colonization factor. The piglets infected with ED can die suddenly or manifested as edema in eyelids and face, ataxia, convulsion or paralysis. Control of the disease still faces a challenge as no efficient preventive measures existed so far. Therefore, the aim of this PhD was to develop a new immunization strategy against ED.To better understand the epidemiology of ED, the Stx2e and F18 sero-surveilance in pigs of Vietnam was carried out. The levels of serum Stx2e and F18 antibodies were evaluated by the ELISA. From the serological data, F18 fimbriated E. coli was highly prevalent and widespread in pigs of Vietnam. Moreover, the distribution of serum Stx2e and F18 antibodies was significantly different between sows, finishing pigs. Thereafter, E. coli associated with ED in piglets from northern Vietnam were characterized. In this regard all of E. coli strains isolated from ED cases were positive for both the Stx2e toxin and the F18 gene. Forty-six (67%) of the 69 Stx2e+/F18+E. coli isolates belonged to classical serotypes while the remaining strains did not belong to the common serotypes in pig. Moreover, very high level of multiple drug resistance was observed among ED causing E. coli strains with 84% of the isolates resistant to five or more antibiotics. To allow the development of broad-spectrum vaccine, an ideal candidate antigen should be well conserved among pathogenic strains. The Stx2e genes of 23 E. co li strains isolated from ED cases in piglets from different geographic regions in Vietnam were sequenced and analyzed. Alignment deduced amino acid sequences of the selected isolates and the published Stx2e sequences of E. coli strains causing ED from Gene bank showed identity of 100 %. Comparisons with the available Stx2e sequences of E. coli strains isolated from human, healthy pig, environment and food also revealed more than 99% identity. A double mutation in the stx2e subunit A gene was created introducing two substitutions at position 167 from glutamate to glutamine (E167Q) and at position 77 from tyrosine to serine (Y77S). The resulting Stx2e toxoid (Y77S; E167Q) was tested on piglets. Immunization of suckling piglets with the Stx2e toxoid was safe and efficiently prevented ED clinical symptom development after challenge with the Stx2e toxin. Moreover, a new approach of maternal immunization was explored. High levels of maternal specific Stx2e antibodies, produced after immunizing pregnant sows with Stx2e toxoid, were successfully transmitted to the offspring and alsoeffectively protected the weaned piglets from a challenge with a lethal dose of the Stx2e toxin.

antibodies --- Vaccination --- Swine --- Escherichia coli --- Resistance to antibiotics --- Disease control --- Viet Nam --- Academic collection --- Theses

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Food --- Escherichia coli infections --- Cattle --- Safety measures. --- Prevention. --- Safety measures --- Government policy