Improving Our Understanding of Salmonella enterica Serovar Paratyphi B through the Engineering and Testing of a Live Attenuated Vaccine Strain.

Enteric fever is caused by three Salmonella enterica serovars: Typhi, Paratyphi A, and Paratyphi B sensu stricto Although vaccines against two of these serovars are licensed (Typhi) or in clinical development (Paratyphi A), as yet there are no candidates for S. Paratyphi B. To gain genomic insight into these serovars, we sequenced 38 enteric fever-associated strains from Chile and compared these with reference genomes. Each of the serovars was separated genomically based on the core genome. Genomic comparisons identified loci that were aberrant between serovars Paratyphi B sensu stricto and Paratyphi B Java, which is typically associated with gastroenteritis; however, the majority of these were annotated as hypothetical or phage related and thus were not ideal vaccine candidates. With the genomic information in hand, we engineered a live attenuated S. Paratyphi B sensu stricto vaccine strain, CVD 2005, which was capable of protecting mice from both homologous challenge and heterologous challenge with S. Paratyphi B Java. These findings extend our understanding of S. Paratyphi B and provide a viable vaccine option for inclusion in a trivalent live attenuated enteric fever vaccine formulation.IMPORTANCE We developed a live attenuated Salmonella enterica serovar Paratyphi B vaccine that conferred protection in mice against challenge with S Paratyphi B sensu stricto and S Paratyphi B Java, which are the causes of enteric fever and gastroenteritis, respectively. Currently, the incidence of invasive S. Paratyphi B sensu stricto infections is low; however, the development of new conjugate vaccines against other enteric fever serovars could lead to the emergence of S. Paratyphi B to fill the niche left by these other pathogens. As such, an effective S. Paratyphi B vaccine would be a useful tool in the armamentarium against Salmonella infections. Comparative genomics confirmed the serovar-specific groupings of these isolates and revealed that there are a limited number of genetic differences between the sensu stricto and Java strains, which are mostly hypothetical and phage-encoded proteins. The observed level of genomic similarity likely explains why we observe some cross-protection.

Implementation of Interventions for the Control of Typhoid Fever in Low- and Middle-Income Countries.

Past research has focused on typhoid fever surveillance with little attention to implementation methods or effectiveness of control interventions. This study purposefully sampled key informants working in public health in Chile, India, Pakistan, Bangladesh, Thailand, Vietnam, South Africa, and Nigeria to 1) scope typhoid-relevant interventions implemented between 1990 and 2015 and 2) explore contextual factors perceived to be associated with their implementation, based on the Consolidated Framework for Implementation Research (CFIR). We used a mixed methods design and collected quantitative data (CFIR questionnaire) and qualitative data (interviews with 34 public health experts). Interview data were analyzed using a deductive qualitative content analysis and summary descriptive statistics are provided for the CFIR data. Despite relatively few typhoid-specific interventions reportedly implemented in these countries, interventions for diarrheal disease control and regulations for food safety and food handlers were common. Most countries implemented agricultural and sewage treatment practices, yet few addressed the control of antibiotic medication. Several contextual factors were perceived to have influenced the implementation of typhoid interventions, either as enablers (e.g., economic development) or barriers (e.g., limited resources and habitual behaviors). Consolidated Framework for Implementation Research factors rated as important in the implementation of typhoid interventions were remarkably consistent across countries. The findings provide a snapshot of typhoid-relevant interventions implemented over 25 years and highlight factors associated with implementation success from the perspective of a sample of key informants. These findings can inform systematic investigations of the implementation of typhoid control interventions and contribute to a better understanding of the direct effects of implementation efforts.

Typhoid fever vaccination strategies.

Typhoid vaccination is an important component of typhoid fever prevention and control, and is recommended for public health programmatic use in both endemic and outbreak settings. We reviewed experiences with various vaccination strategies using the currently available typhoid vaccines (injectable Vi polysaccharide vaccine [ViPS], oral Ty21a vaccine, and injectable typhoid conjugate vaccine [TCV]). We assessed the rationale, acceptability, effectiveness, impact and implementation lessons of these strategies to inform effective typhoid vaccination strategies for the future. Vaccination strategies were categorized by vaccine disease control strategy (preemptive use for endemic disease or to prevent an outbreak, and reactive use for outbreak control) and vaccine delivery strategy (community-based routine, community-based campaign and school-based). Almost all public health typhoid vaccination programs used ViPS vaccine and have been in countries of Asia, with one example in the Pacific and one experience using the Ty21a vaccine in South America. All vaccination strategies were found to be acceptable, feasible and effective in the settings evaluated; evidence of impact, where available, was strongest in endemic settings and in the short- to medium-term. Vaccination was cost-effective in high-incidence but not low-incidence settings. Experience in disaster and outbreak settings remains limited. TCVs have recently become available and none are WHO-prequalified yet; no program experience with TCVs was found in published literature. Despite the demonstrated success of several typhoid vaccination strategies, typhoid vaccines remain underused. Implementation lessons should be applied to design optimal vaccination strategies using TCVs which have several anticipated advantages, such as potential for use in infant immunization programs and longer duration of protection, over the ViPS and Ty21a vaccines for typhoid prevention and control.

Therapeutic effects of Salmonella typhi in a mouse model of T-cell lymphoma.

In this study, we assessed the effectiveness of a live, attenuated Salmonella enterica serovar Typhi (S. Typhi) vaccine strain as a cancer immunotherapy in a mouse model of metastatic T-cell lymphoma. EL4 tumor-bearing C57BL/6J mice immunized with S. Typhi strain CVD 915, by injection into the tumor and the draining lymph node areas, displayed a significant decrease in tumor growth, a reduction in the mitotic index (MI) of tumors, a delayed development of palpable lymph node metastases and most importantly improved survival, compared to untreated mice. Besides, complete tumor regression was achieved in a small number of bacteria-treated mice. A successful therapeutic response associated with a significant reduction of tumor mass was evident as early as 5 days after treatment. The administration of Salmonella to tumor-bearing mice promoted early cellular infiltration (mainly neutrophils) within the tumor, and was accompanied by a decreased intratumoral interleukin 10 production as well as by leukocyte expansion in tumor draining lymph nodes. A tumor-specific memory immune response was induced in most of cured animals, as evidenced by the lack of tumor growth after a rechallenge with the same tumor. EL4 cells cultured with live Salmonella failed to proliferate and underwent apoptosis in a dose-dependent, time-dependent, and contact-dependent manner. To our knowledge, these results demonstrate for the first time the efficacy of a S. Typhi vaccine strain as an oncolytic and immunotherapeutic agent against a highly malignant tumor and support the use of S. Typhi-based vaccine strains in cancer therapy.

Immune adjuvant effect of V. cholerae O1 derived Proteoliposome coadministered by intranasal route with Vi polysaccharide from Salmonella Typhi.

The proteoliposome derived from Vibrio cholerae O1 (PLc) is a nanoscaled structure obtained by a detergent extraction process. Intranasal (i.n) administration of PLc was immunogenic at mucosal and systemic level vs. V. cholerae; however the adjuvant potential of this structure for non-cholera antigens has not been proven yet. The aim of this work was to evaluate the effect of coadministering PLc with the Vi polysaccharide antigen (Poli Vi) of S. Typhi by the i.n route. The results showed that Poli Vi coadministered with PLc (PLc+Poli Vi) induce a higher IgA response in saliva (p<0.01) and faeces (p<0.01) than Poli Vi administered alone. Likewise, the IgG response in sera was higher in animals immunised with PLc+Poli Vi (p<0.01). Furthermore, IgG induced in sera of mice immunised with PLc+Poli Vi was similar (p>0.05) to that induced in a group of mice immunised by the parenteral route with the Cuban anti-typhoid vaccine vax-TyVi, although this vaccine did not induce a mucosal response. In conclusion, this work demonstrates that PLc can be used as a mucosal adjuvant to potentiate the immune response against a polysaccharide antigen like Poli Vi.

Ty21a live oral typhoid vaccine and prevention of paratyphoid fever caused by Salmonella enterica Serovar Paratyphi B.

In randomized, controlled field trials in Area Norte and Area Occidente of Santiago, Chile, 2 (Norte) or 3 (Occidente) doses of live oral typhoid vaccine Ty21a in enteric-coated capsules conferred protection against confirmed Salmonella enterica serovar Typhi disease (53% efficacy in Norte; 67% efficacy in Occidente) during 3 years of follow-up. There was also a trend in each trial showing protection against S. enterica serovar Paratyphi B disease (56% efficacy in Norte; 42% efficacy in Occidente). To enhance statistical power, an analysis was performed using pooled data from the 2 trials; this pooling of data was justified by the following facts: epidemiologic surveillance and microbiological methods were identical, the trials overlapped during 22 of the 36 months of follow-up in each trial, the estimates of efficacy against paratyphoid B fever in the 2 trials were roughly similar, and the ratio of follow-up of vaccine recipients to control subjects in both trials was ~1 : 1. In the pooled analysis, Ty21a conferred significant protection against paratyphoid B fever (efficacy, 49%; 95% confidence interval, 8%-73%; P=.019).

Validación de un ELISA tipo inhibición para cuantificar polisacárido Vi en la vacuna antitifoídica cubana vax-TyVi / Validation of an inhibition-type ELISA for quantifying Vi polysaccharide content in the Cuban

Se describe la validación de un ELISA tipo inhibición, reportado por primera vez en la literatura científica para cuantificar un antígeno vacunal: el polisacárido Vi de Salmonella Typhi, para ser empleado en el control de la calidad de la vacuna antitifoídica cubana vax-TyVi‚. El ensayo consta de seis pasos: 1) Recubrimiento de placa de reacción con poli-L-lisina y posteriormente polisacárido Vi; 2) Bloqueo con leche descremada; 3) Inhibición o neutralización en tubos de suero anti-Vi de conejo, respectivamente, con polisacárido Vi de Curva de Calibración (concentraciones desde 1–32 µg/mL), control positivo y muestras de vacuna (3 diluciones); 4) Neutralización de anticuerpos anti-Vi libres, presentes en las mezclas anteriores, por el Polisacárido de Recubrimiento; 5) Reconocimiento de anticuerpos anti-Vi unidos a la placa (conjugado anti-IgG de conejo-fosfatasa alcalina) y 6) Revelado por reacción enzima-sustrato. Los parámetros de validación estudiados y sus resultados fueron: 1) Precisión, expresada como coeficiente de variación a tres niveles de concentración de polisacárido, comprendidos en el rango de su especificación (35, 50 y 70 µg/mL) y evaluada en términos de repetibilidad; precisión intraensayos (cuatro analistas) y reproducibilidad (seis analistas): £ 20por ciento; 2) Linealidad (100*R2): 99,68 por ciento; 3) Límite de detección: 0,5 µg/mL; 4) Exactitud (recuperación para las tres diluciones de la muestra: entre 100 y 118por ciento), y 5) Robustez: no influye 1,5 h de bloqueo (p = 0,52) ni ± 5 min para leer placa (p = 0,56); influye grandemente la calidad del agua (p = 0,026), a favor del agua para inyección. El ensayo es adecuado para los fines propuestos y es una medida de la inmunogenicidad in vitro del polisacárido Vi(AU)

Estudio de inmunogenicidad de la vacuna antitifoídica cubana de / polisacárido Vi vax-TyVi® en ratones / Study of immunogenicity in mice of the Cuban Vi Polysaccharide Typhoid vaccine, vax-Tyvi

Salmonella enterica serovar Typhi es un microorganismo que provoca más de 16 millones de casos de fiebre tifoidea con aproximadamente 600 000 muertes al año en todo el mundo. Dentro de las vacunas antitifoídicas la de polisacárido capsular Vi ha encontrado, gracias a sus incuestionables ventajas, una gran aceptación entre productores y consumidores. El presente trabajo aborda el estudio de inmunogenicidad de la vacuna antitifoídica cubana de polisacárido Vi vax-TyVi‚ en ratones. El estudio estuvo conformado por un grupo control no inoculado y un segundo grupo que recibió 0,05 mL de la vacuna por vía intramuscular. Se tomaron muestras de sangre a los -3, 7, 14, 21, 28, 42, 56 y 84 días. La actividad de anticuerpos IgG antipolisacárido Vi de los sueros individuales fue determinada por ELISA. Los datos fueron analizados por grupo y por sexo y se calculó el porcentaje de seroconversión, considerándose respondedor aquel animal que al menos aumentara en cuatro veces su título inicial. La respuesta de anticuerpos inducida por la vacuna mostró un aumento notable de los títulos de IgG antipolisacárido Vi en el grupo vacunado (100 por ciento de seroconversión), mientras que el grupo control no incrementó sus niveles mínimos iniciales (0por ciento de respondedores). Aunque más dispersa, la respuesta de anticuerpos antiVi fue significativamente mayor en las hembras que en los machos(AU)

Seguridad e inmunogenicidad de una vacuna de polisacárido Vi de salmonella typhi en jóvenes cubanos / Security and immunogenecity of a vaccine of polyssacharide Vi from salmonella typhi in cuban youths

Se realizó un estudio aleatorizado, controlado y a doble ciegas, en adultos jóvenes de 18 a 20 años, con el objetivo de evaluar la reactogenicidad y la inmunogenicidad de vax-TyViâ, vacuna de polisacárido Vi de Salmonella typhi. Se distribuyeron en 3 grupos; inmunizados con una dosis de vax-TyViâ (Instituto Finlay), TYPHIM ViTM (Pasteur-Mérieux) o vax-TETâ (toxoide tetánico). Se tomaron muestras de suero antes y 21 d después de la inmunización. La inmunogenicidad se evaluó en 323 voluntarios mediante un ELISA indirecto. La seroconversión de los que recibieron vax-TyViâ fue 81,97 por ciento y de 65,05 por ciento para TYPHIM ViTM. Los títulos medios geométricos posvacunales fueron 7,41 U/mL (5,92–9,27 U/mL) y 5,41 U/mL (4,35–6,72 U/mL) respectivamente. La seroconversión con vax-TETâ fue 0 por ciento. La reactogenicidad de ambas vacunas polisacarídicas fue baja. Se concluyó que la inmunogenicidad de vax-TyViâ no fue inferior a la de TYPHIM ViTM y su reactogenicidad resultó similar(AU)

Immunogenicity of a new Salmonella Typhi Vi polysaccharide vaccine--vax-TyVi--in Cuban school children and teenagers.

A randomized, controlled, double blind study was carried out in Cuban children and teenagers aged 9-13 years to evaluate the immunogenicity of vax-TyVi-Salmonella Typhi Vi polysaccharide vaccine-with respect control vaccines. Serum samples were taken before and 21 days after the immunization, and ELISA was used for the determination of antibodies to Vi polysaccharide. Subjects who received vax-TyVi and TYPHIM Vi (Pasteur-Mérieux) showed seroconversion rates of 85.61 and 78.36%, respectively. The geometric mean titer (GMT) values for Vi antibodies induced after vaccination were 6.27 microg/ml (5.40-7.38 microg/ml) and 5.97 microg/ml (5.01-7.10 microg/ml), respectively. In contrast, subjects receiving the tetanus toxoid vaccine showed 0% seroconversion.

Investigation of the response to the enterobacterial common antigen after typhoid vaccination

Anticorpos contra o antígeno comum de enterobactérias (ECA) bem como contra os antígenos somáticos (O) e flagelar (H) de Salmonella typhi foram investigados no soro de recrutas do sexo masculino, após a vacinaçäo. Näo foi detectada resposta humoral para ECA. Os soros obtidos antes da vacinaçäo mostraram hemaglutininas para ECA acompanhando a presença de aglutininas para o antígeno H, ao contrário do que se observou em relaçäo ao antígeno O. Discutem-se os resultados quanto ao possível mecanismo da imunoproteçäo da febre tifóide

Immunogenicity of Ty21a attenuated "Salmonella typhi" given with sodium bicarbonate or in enteric-coated capsules.

Ty21a, a stable attenuated mutant of Salmonella typhi, is a safe, protective oral vaccine when 3 doses of 10(9) cells in saline are taken after neutralization of gastric acidity by 1 g NaHCO3. To identify a more convenient method to administer vaccine and to determine the feasibility of immunizing with a single dose, we studied the immune response of children and adults to different formulations of Ty21a with a newly developed, sensitive, enzyme-linked immunosorbent assay (ELISA). In this ELISA, a rise in S. typhi O antibody was defined as a change in net optical density of greater than or equal to 0.15 (more than 3 SD from the mean difference in optical density in a negative control population). Three hundred and thirty-five Chilean children were given 3 doses of 10(9) Ty21a in 150 ml of milk with 0.8 g NaHCO3 or in enteric-coated capsules. In each group, 5% seroconverted by Widal O but 41% by IgG ELISA O antibody titers; mean antibody levels by group were identical. Studies were also carried out in healthy college students in a non-endemic area (U.S.A.) who had no history of prior typhoid immunization. In total, 141 U.S. adults received vaccine formulated in either one of two ways: 1) in gelatin capsules administered with two additional gelatin capsules containing a total of 0.8 gm NaHCO3 or 2) in enteric-coated capsules. Thirty-six persons received one dose, 30 got two doses and 16 ingested three doses of enteric-coated vaccines, while 44 persons receiving one dose and 15 got two doses of vaccine in the gelatin capsule formulation. Rates of seroconversion of ELISA O antibody were similar in all the groups. Ty21a vaccine was not recovered from multiple stool, jejunal fluid or blood cultures of the U.S. vaccine recipients. Based on these observations a large-scale field trial of efficacy has been initiated in 90.000 schoolchildren 6-20 years of age in Santiago, Chile, of whom one-third received one dose of enteric-coated vaccine, one-third got two doses and the remainder received placebo.