Enteric fever (typhoid), affects about 22 million people and causes about 200,000 deaths every year, according to conservative estimates. Enteric fever is spread by bacteria belonging to the Salmonella genus, with two sub-species – Salmonella Typhi and Salmonella Paratyphi A – being responsible for most cases of the disease. And although the number of cases of enteric fever has fallen significantly over recent decades, there is a clear need for a diagnostic test for Salmonella that is rapid, affordable and accurate. It is important to be able to distinguish between enteric fever caused by Salmonella Typhi and enteric fever caused by Salmonella Paratyphi A in order to ensure that the correct drugs are prescribed and to combat the development of antibiotic resistance.
The application of metabolomics is relatively new in infectious diseases research compared to the application of genomics and proteomics. Despite this, screening the metabolome in blood plasma has identified useful prognostic profiles of several diseases, including sepsis. One of the major benefits of this technique is that it utilizes a pattern of biomarkers (that is, the various metabolites), as opposed to relying on just one host biomarker, as has been the focus of previous approaches.
A new paper in eLife applies this promising new approach to this challenge. Instead of trying to detect Salmonella in the blood during infection, they used a technique called metabolomics. The basic idea of this approach is that infection leads to metabolic changes, such that a person with enteric fever (or any infection) could have a profile of metabolites in their blood that is different to the metabolite profile of a healthy person. The challenge, therefore, is to identify a ‘metabolic fingerprint’ that can be used to detect enteric fever with high levels of sensitivity and specificity.