Shigellosis

Shigellosis, characterized by the frequent passage of loose stools mixed with visible blood accompanied by fever, abdominal cramps, and tenesmus, is an important cause of morbidity and mortality, particularly in children below 5 years of age in developing countries. The causative agent is Shigella spp., consisting of four serogroups, S. sonnei, S. boydii, S. flexneri, and S. dysenteriae. Shigellosis can occur in sporadic and epidemic forms. S. dysenteriae type 1 caused large epidemics in 10-year intervals up to the 1990s but has become rare. Most cases of shigellosis recover rapidly with appropriate antibiotic therapy. However, S. dysenteriae type 1 can be multiple-drug-resistant. Transmission of resistance occurs by clonal spread, especially of S. dysenteriae type 1, and by horizontal transfer through plasmids, transposon-mediated conjugation, and mutations in the chromosome. Multidrug-resistant genes in the integrons of the organism and its epidemic nature make shigellosis a challenging public health problem to tackle. Clonal spread of multidrug-resistant S. dysenteriae type 1 may result in large epidemics. Prevention and control strategies should mainly be focused on the supply of safe drinking water, provision of proper and adequate sanitation facilities, and maintenance of good personal hygiene. Emphasis should be given to handwashing. Vaccination for infectious diseases is an attractive, cost-effective disease-prevention strategy. However, vaccine development for shigellosis must overcome considerable challenges in that shigellosis is caused by four serogroups, each with multiple serotypes. Immunity to Shigella is serotype-specific; thus, a polyvalent vaccine may be needed for prevention; IpaB and IpaC were found to be safe and immunogenic and remain in clinical development. However, decades of research have yet to result in the registration of a successful vaccine candidate.