Typhoid fever & vaccine development: a partially answered question.

Typhoid fever is a systemic disease caused by the human specific Gram-negative pathogen Salmonella enterica serovar Typhi (S. Typhi). The extra-intestinal infections caused by Salmonella are very fatal. The incidence of typhoid fever remains very high in impoverished areas and the emergence of multidrug resistance has made the situation worse. To combat and to reduce the morbidity and mortality caused by typhoid fever, many preventive measures and strategies have been employed, the most important being vaccination. In recent years, many Salmonella vaccines have been developed including live attenuated as well as DNA vaccines and their clinical trials have shown encouraging results. But with the increasing antibiotic resistance, the development of potent vaccine candidate for typhoid fever is a need of the hour. This review discusses the latest trends in the typhoid vaccine development and the clinical trials which are underway.

Immunoblot analysis of sera in uncomplicated typhoid fever & with typhoid ileal perforation.

Background & objectives: Ileal perforation is a serious complication of typhoid fever. The exact reasons for the development of perforation in only a few of those infected with Salmonella Typhi is unknown, and it is likely that immunological factors are involved. Therefore we undertook this study to compare the antibody profile in patients with uncomplicated typhoid fever with those having ileal perforation by immunoblotting. Methods: Two groups of patients were included in the study. Group II comprised patients with uncomplicated typhoid fever (n=47), and group I with typhoid ileal perforation (n=33). The flagellar (H), lipopolysaccharide (LPS) and outer membrane protein (OMP) antigens of Salmonella Typhi were extracted and used to test patient sera for antibodies by immunoblotting Results: Immunoblotting using S. Typhi antigens enabled the detection of S. Typhi antibodies in the two groups of patients. A significant difference was seen in the response of these two groups of patients with respect to antibodies to flagella, lipopolysaccharide and outer membrane proteins. Antibodies to flagella were more pronounced among patients with uncomplicated typhoid fever, while anti-OMP antibodies were significantly associated with typhoid ileal perforation. Interpretation & conclusions: A comparison of antibodies in patients with uncomplicated typhoid fever and with ileal perforation revealed the differences in the antibody profiles of the two groups. Our study suggests that the difference in antibody response may in some way play a role in the pathogenesis of typhoid ileal perforation which can also potentially be exploited to develop suitable diagnostic tests.

Immunological, cellular and molecular events in typhoid fever.

Salmonella, a facultative intracellular Gram-negative bacterium infects a wide range of hosts causing several gastrointestinal diseases and enteric fever in humans and certain animal species. Typhoid caused by Salmonella typhi remains a major health concern in India and worldwide. Also, with emergence of multidrug resistant strains, Salmonella has acquired increased virulence, communicability and survivability, resulting in increased morbidity and mortality. Though a number of vaccines for typhoid are available against S. typhi (or also against S. typhimurium), these have certain undesirable side effects and the search for new immunogens suitable for vaccine formulation is still continuing. The immune response to primary Salmonella infection involves both humoral and cell-mediated responses. The protective immunity against Salmonella depends on host- parasite interaction, however; the detailed mechanism of virulence, innate resistance and susceptibility of host remains unclear. This review focuses on the molecular, immunological and cellular mechanisms of pathogenesis of Salmonella infection to provide an insight to counteract bacterial infections and allow a better understanding of its clinical manifestations. It also reviews better technological possibilities combined with increased knowledge in related fields such as immunology and molecular biology and allow for new vaccination strategies. Some new approaches such as subunit and nucleic acid vaccines and recombinant antigen which are becoming increasingly important for the development of potential vaccines have also been discussed. A significant progress has been made in our understanding of Salmonella pathogenesis. Despite these efforts, however, many challenges exist, especially for investigators who aim to understand how the pathogenic mechanisms operating in vitro apply to in vivo model systems. However, unyielding work and collaborations between Salmonella researchers and clinicians worldwide have made significant contributions to understanding the interaction between virulence determinants and immunity required to stop the spread of this pathogen.

Efficacy of Purified Vi Polysaccharide Typhoid Vaccine

This experiment was conducted to assess the efficacy of typhoid vaccine newly produced by purifying Vi antigen of Salmonella typhi. With Karber method, LD50 of challenging organism (S. typhi ty2) was determined as 6.31 CFU/mouse, and then the organism was used for the study. With Probits method, ED50 of the vaccine was determined as 0.016 microgram / 0.5 ml / mouse. The ELISA titer (0.5097+/-0.0606) was 4 times in the group treated with high dose (0.25 microgram/0.5ml) as in control (0.1113+/-0.0110). Six major protein bands of 66, 55, 35, 33, 18, and 9 kd were detected in Western blot analysis with serum of a vaccine treated mouse, whereas only one weak band of about 35 kd was detected with serum of a control mouse. We concluded that typhoid vaccine produced by purifying Vi antigen of S. typhi very effectively prevent S. typhi infection in mice.

Encuesta inmunológica en la población infantil / Immunologic survey in children in Mexico city

Se presentan los resultados de la evaluación de la reacción de fijación en superficie aplicada al diagnóstico de infecciones por Salmonella Typhosa. Esta reacción a la luz de nuestros datos, demostró ser útil (con alto grado de especificidad) en la detección de anticuerpos contra S. thyphosa, existiendo sin embargo, reacciones cruzadas con salmonelas que poseen antígenos somáticos otras salmonelosis, shigelosis, o infecciones por Escherichia coli, tampoco se les encontró en 104 pacientes con diversos padecimientos infecciosos distintos de fiebre tifoidea. El 100 por ciento de 12 conejos inmunizados con S. typhosa presentó reacción de fijación en superficie positiva, así como el 99 por ciento de 102 niños con tifoidea comprobada bacteriológicamente. En este último grupo, la reacción se hizo positiva, en el 95 por ciento de los casos, desde la primera semana de evolución aparente del padecimiento y empezó a negativizarse a partir del segundo mes. Con la misma reacción se practicó investigación de anticuerpos contra S. typhosa en 2,698 niños aparentemente sanos residentes en el distrito Federal, provenientes de 3 estratos socioeconómicos. El 19.2 por ciento reveló tener anticuerpos, pero dicho porcentaje varió de acuerdo con las condiciones de saneamiento, del 7.5 por ciento en las zonas donde era satisfactorio, al 35.5 por ciento en donde era pésimo. La proporción de positivos aumentó con la edad, obteniéndose el mayor incremento a partir de los 6 años, edad en que entran a la escuela. Se fijan los límites de intensidad de la reacción de fijación en superficie, a partir de los cuales se le pueden dar valor diagnóstico en fiebre tifoidea. Esto se hizo con base a los resultados de la encuesta, tomando en cuenta el número de reactores positivos no tifoídicos, según la edad y el estrato socioeconómico

Antibody response to Salmonella typhi in human schistosomiasis mansoni

Antibody response to Salmonella typhi O and H antigens was evaluated in 24 individuals with either hepatointestinal or hepatosplenic schistosomiasis mansoni before and after typhoid vaccination, and compared with that of non-infected controls. Before vaccination, Schistosoma-infected patients showed a higher frequency of positive antibody to O antigen and the same frequency to H antigen when compared with that of healthy individuals. However, those with hepatosplenic schistosomiasis showed higher titres of antibody to H antigen than those with hepatointestinal disease or healthy individuals. Infected subjects, particularly those with hepatointestinal disease, showed a decreased response after typhoid vaccine. This diminished ability to mount an immune response towards typhoid antigens during schistosomiasis may interfere with the clearance of the bacteria from blood stream and, therefore, play a role in the prolonged survival of salmonella as observed in some patients with chronic salmonellosis associated with schistosomiasis.

Production of monoclonal antibodies to Vi polysaccharide antigen of Salmonella typhi.

Twenty-four Vi antigen-specific monoclonal antibodies were produced in this study. The MAbs were found to be highly specific to Vi possessing bacteria. Selected MAbs were used in a direct agglutination assay for rapid identification of S. typhi in primary bacterial culture and also used to develop an assay to detect Vi antigen in clinical specimens. The result showed that they could not detect the antigen in urine and serum from acute patients even they could detect as low as 0.02 micrograms/ml of Vi antigen added in normal urine. The study has shown that these MAbs are very useful for rapid identification of S. typhi in primary bacterial culture and they can replace polyclonal anti-Vi antibodies which have been used routinely in bacteriological laboratories.

Vacunación contra la fiebre tifoidea / Vaccination against typhoid fever

La fiebre tifoidea es una enfermedad infecciosa aguda y febril causada por Salmonella typhi. La infección se adquiere por medio de la ingestión de alimentos o agua masivamente contaminados con la bacteria. Debido a que este microorganismo afecta sólo al ser humano y no hay reservorios animales, el elemento más importante en la cadena de transmisión son los individuos que no presentan sintomatología clínica pero son portadores y excretores activos del agente (portadores asintomáticos). En México, la enfermedad tiene características endémico-epidémicas relacionadas con deficiencias en el saneamiento ambiental y el aprovisionamiento de agua potable. La tasa de letalidad es de alrededor del 1 por ciento, sin embargo en los casos complicados puede ascender hasta el 30 por ciento. La vacuna que se utiliza más ampliamente en la actualidad es la inactivada por calor y fenol, la cual tiene efectos colaterales debido al LPS que siempre lo contamina. Además, confiere protección parcial y de corta duración, por lo tanto su empleo se ha limitado a grupos considerados como de alto riesgo y no está indicada en niños. La vacuna de Germanier -mutante avirulenta de Salmonella que se administra por vía oral- proteje hasta un 95 por ciento, siempre y cuando antes de administrarse se neutralice el jugo gástrico, aunque su utilización general en Salud Pública es impráctica. Ya que las porinas son buenos inmunógenos en modelos animales, la obtención de un conjugado antígenico Vi-porinas puede ser una excelente opción como vacuna contra la fiebre tifoidea

T and B lymphocytes in patients with enteric fever.

Estimation of T and B lymphocytes was done in 50 patients of enteric fever, 50 duration matched non enteric fever patients and 50 normal healthy individuals. The difference in both early and late rosette forming T lymphocytes was found to be statistically significant in enteric versus non-enteric patients. Significant difference was also observed in enteric versus normal individuals in case of late rosette forming T lymphocytes.

Conglutination and passive hemagglutination in rapid diagnosis of typhoid fever

The efficacy of the enrichment work coagglutination and passive hemagglutination techniques in rapid diagnosis of typhoid fever was studied in parallel with the classical [conventional methods of clot cultures and widal agglutination test], on one hundred clinically suspected cases diagnosed as query enteric fever. Antigen detection in their sera was done by coagglutination [COAG] and clot culture as well as antisalmonella antibody which was detected by passive hemagglutination test [PHAG] and widel test. Analysis of data with reference to confirm typhoid fever cases showed that, Salmonella organism was isolated in 16% of clot cultures. This was correlated closely with widel test [23%] in contrast to PHAG [59%] and COAG [73%]. Thus PHAG and COAG were the superior for serological diagnosis of typhoid fever

Specific immune responses in typhoid fever & after TAB vaccination.

The specific immune responses to Salmonella typhi were investigated in 131 patients suffering from typhoid fever and 34 healthy individuals after TAB vaccination. A proportion of individuals failed to develop either specific humoral or cell mediated immune responses. About 5 per cent of the patients with natural infection and nearly 9 per cent of the vaccine recipients failed to develop both the responses. Frequent reinfection and carrier state, and lack of absolute protection following TAB vaccination could be due to the inability of a proportion of naturally infected and TAB vaccinated individuals to mount sufficient specific immune responses, due to the same mechanism.

Fagotipos de salmonella typhi en fiebre tifoidea / Phage-types of salmonella typhi in typhoid fever

Se analizan 175 casos de fiebre tifoidea en niños de 6 meses a 15 años de edad, hospitalizados entre 1982 y 1985, intentando relacionar la gravedad de la presentación clínica con los distintos fagotipos de las S. typhi aisladas de estos enfermos. Comparadas la frecuencia e intensidad de los síntomas y signos clínicos, las alteraciones de los exámenes de laboratorio, la frecuencia de las complicaciones y de las recaídas, no se encuentran diferencias significativas entre los cuatro fagotipos predominantes (E1, 46, A, Vi degradadas). También las cepas mismas mostraron un comportamiento bioquímico y antigénico similar en el estudio de laboratorio, así como una sensibilidad uniforme a cloramfenicol (CIM 100: 4 mcg/ml)

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