VIOLIN: Vaccine Investigation and Online Information Network

Pathogen Page

Salmonella spp.

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

Salmonellosis

3. Introduction

Salmonella serovars, like Salmonella enterica serovars Paratyphi and Typhi, cause an estimated 200,000 deaths per year. Much of it is spread by contaminated food or drinking water. Salmonella disease is mostly found in Africa, South America, and Southeast Asia. In Southeast Asia, the prevalence of typhoidal salmonellosis is high and many patients suffer relapses. Studies are being done to see why the immune system is unable to mount a lasting defense against the bacteria, and how to counteract antibiotic resistance, one of the main difficulties encountered in the protection of the Salmonella vaccine (Boyle et al., 2007).

4. Microbial Pathogenesis

Salmonella first replicates in epithelial cells. It generally targets dendritic cells and macrophages after the mucosal barrier, where it multiplies rapidly (Cheminay and Hensel, 2007). Salmonella infections induce a weak and delayed T cell responses in human typhoid fever and in animal models of typhoid fever, suggesting immunosuppressive effects. Salmonella also directly inhibits T cell proliferations (Cheminay and Hensel, 2007).

5. Host Ranges and Animal Models

S. Typhi only causes infections in humans. S. Typhimurium causes a lethal disease in susceptible mice which resembles in many aspects of human typoid fever. Therefore, S. Typhimurium has been frequently used as a model to study human typhoid fever. S. enterica causes zoonotic gastrointestinal infections from reservoirs in all important livestock animals. Vaccine studies have been done on humans, cattle, mice, and chickens (Boyle et al., 2007; Boyle et al., 2007).

6. Host Protective Immunity

Little information exists regarding the protective immunity and immunological memory for serovar Typhi. B-cell production of soluble antibodies, cytotoxic T lymphocyte activities for killing infected cells, CD4+ and CD8+ T cell homing to the gut, and distinct subsets of memory T cells are shown to be essential for protective immunity against serovar Typhi infection (Boyle et al., 2007). Two vaccines are currently commercially available against typhoid. Typhim Vi (Pasteur Merieux) is a vaccine of purified Vi-antigen from S. Typhi. Vivotif is a live attenuated S. Typhi Ty21 strain, generated by the mutagenesis of the virulent, parental S. Typhi Ty2. The major challenge of vaccine development is balancing immunogenicity and attenuation. Many vaccines have been developed with mutations in regulatory genes encoding adenylate cyclase and cAMP receptor protien (Cheminay and Hensel, 2007).

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