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Oral vaccination against enteric bacterial infections: an overview
Abstract:
The present situation and the future prospects for the use of oral vaccines against the major enteric diseases typhoid fever, shigellosis and cholera are discussed in this paper. No significant protection could be demonstrated for oral inactivated whole-cell vaccines. In contrast, an oral live vaccine based on the attenuated Salmonella typhi strain Ty 21a was highly efficacious in volunteer challenge studies and in a controlled field trial. Two attenuated strains are presently being tested in volunteer studies as candidate vaccines against shigellosis; one uses S. typhi Ty 21a and the other Escherichia coli K-12 as the carrier for shigella antigens. Experimental challenge studies in volunteers showed that recovery from clinical cholera confers solid and long-lasting protection. The goal of present research is to develop a vaccine that mimics the events of clinical cholera without causing disease.
Insights
Oral live vaccines, particularly Salmonella typhi strain Ty 21a, show promise for preventing typhoid fever. Research is ongoing for shigellosis and cholera vaccines that mimic natural immunity without causing illness.
Area of Science:
- Microbiology
- Vaccinology
- Infectious Diseases
Background:
- Enteric diseases like typhoid fever, shigellosis, and cholera pose significant global health challenges.
- Current vaccine strategies for these diseases are under development, with a focus on oral delivery methods.
Purpose of the Study:
- To review the current status and future potential of oral vaccines against major enteric pathogens.
- To evaluate the efficacy of different oral vaccine candidates for typhoid fever, shigellosis, and cholera.
Main Methods:
- Assessment of inactivated whole-cell oral vaccines.
- Evaluation of live attenuated oral vaccines, including Salmonella typhi strain Ty 21a.
- Review of volunteer challenge studies and field trials for vaccine efficacy.
- Analysis of natural immunity conferred by clinical cholera.
Main Results:
- Oral inactivated whole-cell vaccines demonstrated no significant protective effect.
- An oral live vaccine using attenuated Salmonella typhi strain Ty 21a proved highly effective in challenge studies and field trials.
- Candidate vaccines for shigellosis utilizing S. typhi Ty 21a or E. coli K-12 as carriers are under investigation.
- Recovery from clinical cholera provides robust, long-term protection.
Conclusions:
- Live attenuated oral vaccines, exemplified by Salmonella typhi strain Ty 21a, are a promising approach for typhoid fever prevention.
- Further research is needed to develop effective oral vaccines for shigellosis and cholera.
- Mimicking the protective immune response of natural cholera infection is a key goal for future cholera vaccine development.