Invasive non-typhoidal Salmonella (iNTS) disease is a clinical condition distinct from Salmonella gastroenteritis. With an overall case fatality rate of 14.5% iNTS remains a major cause of morbidity and mortality, particularly in sub-Saharan Africa. However, the sources of infections that lead to cases of iNTS remain unclear. Broadly, there are two hypotheses as to the source of infections i) transmission from a zoonotic reservoir, similar to other non-typhoidal Salmonelloses or ii) person-to-person transmission. Here we review several recent studies that have asked “what is the source of infections causing invasive non-typhoidal Salmonella disease?”. Two studies reported isolates in the stool of household members of iNTS cases that were very closely related (<3 SNPs) to the iNTS case isolates - this is consistent with the hypothesis of person-to-person transmission, but infection from a common source (e.g. a foodstuff) cannot be excluded. On the other hand, thorough investigations of the domestic environment of iNTS cases and the food pathway found only a single iNTS-associated Enteritidis isolate. Therefore, we recommend that future studies test the hypothesis that iNTS is transmitted between people within the domestic environment. Further studies of food and water pathways are also warranted.
Salmonella Typhimurium and Salmonella Enteritidis are leading causative agents of invasive nontyphoidal Salmonella (iNTS) disease, which represents one of the major causes of death and morbidity in sub-Saharan Africa, still partially underestimated. Large sero-epidemiological studies are necessary to unravel the burden of disease and guide the introduction of vaccines that are not yet available. Even if no correlate of protection has been determined so far for iNTS, the evaluation of complement-mediated functionality of antibodies generated towards natural infection or elicited upon vaccination may represent a big step towards this achievement. Here we present the setup and the intra-laboratory characterization in terms of repeatability, intermediate precision, linearity, and specificity of a high-throughput luminescence-based serum bactericidal assay (L-SBA). This method could be useful to perform sero-epidemiological studies across iNTS endemic countries and for evaluation of antibodies raised against iNTS vaccine candidates in upcoming clinical trials.
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