Salmonella, Enteric Fevers, and Salmonellosis


Published on:
September 12, 2019

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Citation:

Hasan, R., Nordin, A.C., Shakoor, S., Keenum, I. and Vinneras, B. 2019. Salmonella, Enteric Fevers, and Salmonellosis. In: J.B. Rose and B. Jiménez-Cisneros, (eds) Global Water Pathogen Project. http://www.waterpathogens.org ( A. Pruden, N. Ashbolt and J. Miller (eds) Part 3 Baceteria) http://www.waterpathogens.org/book/salmonella-enteric-fevers-salmonellosis. Michigan State University, E. Lansing, MI, UNESCO.
https://doi.org/10.14321/waterpathogens.27

Acknowledgements: K.R.L. Young, Project Design editor; Website Design: Agroknow (http://www.agroknow.com)

Last published: September 12, 2019
Authors: 
Rumina Hasan (The Aga Khan University , London School of Hygiene and Tropical Medicine)Annika C. Nordin (Swedish University of Agricultural Sciences)Sadia Shakoor (The Aga Khan University )Ishi Keenum (Virginia Tech)Björn Vinneras (Swedish University of Agricultural Sciences)

Summary

Salmonella species are widespread across the globe and associated with both human and animal hosts. The genus Salmonella includes the species S. enterica. S. enterica is further subdivided into subspecies amongst which Salmonella enterica subspecies enterica includes many of pathogens important for human disease. While newer molecular methods provide good species and subspecies level discrimination for Salmonella, many laboratories still rely on antigenic structure based on the initial Kauffman-White-Le Minor (KWL) scheme which remains valid.

In humans, Salmonella infections are most prevalent in low-to-middle income countries and are divided into infections caused by typhoidal and non-typhoidal salmonellae. Typhoidal salmonellae; Salmonella enterica serovars Typhi, Paratyphi A, B and C are restricted to human hosts and associated with invasive disease (enteric fever). Non-typhoidal salmonellae (NTS), which may be of zoonotic origin, are primarily associated with non-invasive disease. In both Africa and Asia, burden of salmonella infections is highest in children. Salmonella strains show geographical differences with different strain types being prevalent in different regions.

Clinically, enteric fever typically presents with fever and gastrointestinal symptoms. Complications include intestinal bleeding/perforation (in older children and adults) and paralytic ileus in younger children. Additional complications include cardiopulmonary disorders, bronchopneumonia, thrombocytopenia/anaemia (particularly amongst children in Africa), as well as sepsis. NTS infections are typically associated with gastroenteritis, although in immunocompromised (e.g., in patients with HIV), NTS may also result in invasive disease. It is suggested that genomic differences may be linked to non-invasive versus invasive behaviour of Salmonella strains.

The main reservoir for salmonellae is the gastrointestinal tract of vertebrates, with bacteria being shed in stool. Spread is through the fecal-oral route. Environmental factors; including contaminated food, water and poor hand hygiene, contribute to dissemination. Prevention of Salmonella infections centers on safe water, sanitation and hygiene, food safety, and vaccination where available. Commercial vaccines are available for human use against the enteric or typhoid fever causing S. Typhi, and newer conjugate vaccines may have longer lasting immunity than capsular polysaccharide vaccine precursors.

Treatment technologies for reduction of Salmonella in wastewater fractions can be divided into three main types: chemical, biological and thermal. When comparing the inactivation of Salmonella spp. with Escherichia coli, the latter is somewhat more resistant to most treatments and can therefore be used as a proper indicator for salmonella during treatments. Salmonella has several genetically-driven responses to stress related to the inactivation treatments, which increase survival during extreme conditions. In this chapter the inactivation time for salmonella in relation to pH, ammonia concentration and temperature is presented. For pH, generated inactivation chemical substances aid in the inactivation: at higher pH uncharged ammonia is the most active molecule enhancing inactivation while at low pH carbonate and organic acids both increase the efficiency of inactivation. For heat inactivation, increased dry matter content increases the time of survival. Biological treatments affect the survival, while also decreasing the number of viable Salmonella over time. However, the effect of the biological treatment is difficult to monitor and quantify and therefore extended treatment durations are recommended for biological treatment if the treatment is not combined with chemical or thermal treatment.

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