Evaluation of a Virus-like Replicon Particle Vaccine Expressing Proteins of Swine Influenza Virus in Pigs With and Without Maternally Derived Antibodies

A major hurdle to swine influenza vaccination of young piglets is maternal antibody interference. This interference is transient as it disappears when pigs reach about 3 months of age. We vaccinated piglets without and with interfering maternal antibody using a recombinant vector vaccine. In the absence of interfering maternal antibody, the vaccine was effective in inducing a strong immune response and greatly reduced the amount of virus. However, this same recombinant vaccine was not effective when interfering maternal antibodies were present. We are currently trying a higher dose of vaccine and different genes from SIV in hopes we can overcome this maternal antibody. Preliminary data from these new studies are promising

\u3ci\u3eEscherichia coli\u3c/i\u3e O157:H7 Requires Intimin for Enteropathogenicity in Calves

Enterohemorrhagic Escherichia coli (EHEC) strains require intimin to induce attaching and effacing (A/E) lesions in newborn piglets. Infection of newborn calves with intimin-positive or intimin-negative EHEC O157: H7 demonstrated that intimin is needed for colonization, A/E lesions, and disease in cattle. These results suggest that experiments to determine if intimin-based vaccines reduce O157:H7 levels in cattle are warranted

Differentiation of F18ab+ from F18ac+ \u3ci\u3eEscherichia coli\u3c/i\u3e by Single-Strand Conformational Polymorphism Analysis of the Major Fimbrial Subunit Gene (\u3ci\u3efedA\u3c/i\u3e)

Toxin-producing Escherichia coli expressing F18 fimbriae colonizes the small intestines of weaned pigs and causes diarrhea, edema disease, or both. The F18 family is composed of two antigenic variants, F18ab and F18ac. Because many strains do not express F18 fimbriae in vitro, identification and differentiation of these two variants are difficult. Single-strand conformational polymorphism (SSCP) analysis is a rapid method for identifying genetic mutations and polymorphisms. The F18 major fimbrial subunit genes (fedA) of 138 strains were amplified by PCR, and genetic differences were detected by SSCP analysis. The SSCP analysis of the fedA gene differentiated F18ab+ strains from F18ac+ strains. Most strains classified as F18ab+ by SSCP analysis contained Shiga toxin 2e and enterotoxin genes. Most strains classified as F18ac+ by SSCP analysis contained only enterotoxin genes. The SSCP analysis was a useful method for predicting the antigenicity of F18+ E. coli and could also be used for analysis of other virulence genes in E. coli and other pathogenic bacteria

Pathogenicity of \u3ci\u3eEscherichia coli\u3c/i\u3e O157:H7 in the Intestines of Neonatal Calves

Cattle are an important reservoir of Shiga toxin-producing enterohemorrhagic Escherichia coli (EHEC) O157:H7 strains, foodborne pathogens that cause hemorrhagic colitis and hemolytic uremic syndrome in humans. EHEC O157:H7 strains are not pathogenic in calves \u3e3 weeks old. Our objective was to determine if EHEC O157:H7 strains are pathogenic in neonatal calves. Calves(A/E) lesions in both the large and small intestines by 18 h postinoculation. The severity of diarrhea and inflammation, and also the frequency and extent of A/E lesions, increased by 3 days postinoculation. We conclude that EHEC O157:H7 strains are pathogenic in neonatal calves. The neonatal calf model is relevant for studying the pathogenesis of EHEC O157:H7 infections in cattle. It should also be useful for identifying ways to reduce EHEC O157:H7 infections in cattle and thus reduce the risk of EHEC O157:H7 disease in humans

Early Attachment Sites for Shiga-Toxigenic \u3ci\u3eEscherichia coli\u3c/i\u3e O157:H7 in Experimentally Inoculated Weaned Calves

Weaned 3- to 4-month-old calves were fasted for 48 h, inoculated with 1010 CFU of Shiga toxin-positive Escherichia coli (STEC) 0157:H7 strain 86-24 (STEC 0157) or STEC 091:H21 strain B2F1 (STEC 091), Shiga toxin-negative E. coli 0157:H7 strain 87-23 (Stx- 0157), or a nonpathogenic control E. coli strain, necropsied 4 days postinoculation, and examined bacteriologically and histologically. Some calves were treated with dexamethasone (DEX) for 5 days (3 days before, on the day of, and 1 day after inoculation). STEC 0157 bacteria were recovered from feces, intestines, or gall bladders of 74% (40/55) of calves 4 days after they were inoculated with STEC 0157. Colon and cecum were sites from which inoculum-type bacteria were most often recovered. Histologic lesions of attaching-and-effacing A/E 0157+ bacteria were observed in 69% (38/55) of the STEC 0157-inoculated calves. Rectum, ileocecal valve, and distal colon were sites most likely to contain A/E 0157+ bacteria. Fecal and intestinal levels of STEC 0157 bacteria were significantly higher and A/E 0157+bacteria were more common in DEX-treated calves than in nontreated calves inoculated with STEC 0157. Fecal STEC 0157 levels were significantly higher than Stx- 0157, STEC 091, or control, or control E. coli; only STEC 0157 cells were recovered from tissues. Identifying the rectum, ileocecal valve, and distal colon as early STEC 0157 colonization sites and finding that DEX treatment enhances the susceptibility of weaned calves to STEC 0157 colonization will facilitate the identification and evaluation of interventions aimed at reducing STEC 0157 infection in cattle

Bovine Immune Response to Shiga-Toxigenic \u3ci\u3eEscherichia coli \u3c/i\u3eO157:H7

Although cattle develop humoral immune responses to Shiga-toxigenic (Stx+) Escherichia coli O157:H7, infections often result in long-term shedding of these human pathogenic bacteria. The objective of this study was to compare humoral and cellular immune responses to Stx+ and Stx- E. coli O157:H7. Three groups of calves were inoculated intrarumenally, twice in a 3-week interval, with different strains of E. coli: a Stx2- producing E. coli O157:H7 strain (Stx2+O157), a Shiga toxin-negative E. coli O157:H7 strain (Stx-O157), or a nonpathogenic E. coli strain (control). Fecal shedding of Stx2+O157 was significantly higher than that of Stx-O157 or the control. Three weeks after the second inoculation, all calves were challenged with Stx2+O157. Following the challenge, levels of fecal shedding of Stx2+O157 were similar in all three groups. Both groups inoculated with an O157 strain developed antibodies to O157 LPS. Calves initially inoculated with Stx-O157, but not those inoculated with Stx2+O157, developed statistically significant lymphoproliferative responses to heat-killed Stx2+O157. These results provide evidence that infections with STEC can suppress the development of specific cellular immune responses in cattle, a finding that will need to be addressed in designing vaccines against E. coli O157:H7 infections in cattle