Development of ELISAs for diagnosis of acute typhoid fever in Nigerian children

Abstract

Improved serodiagnostic tests for typhoid fever (TF) are needed for surveillance, to facilitate patient management, curb antibiotic resistance, and inform public health programs. To address this need, IgA, IgM and IgG ELISAs using Salmonella enterica serovar Typhi (S. Typhi) lipopolysaccharide (LPS) and hemolysin E (t1477) protein were conducted on 86 Nigerian pediatric TF and 29 non-typhoidal Salmonella (NTS) cases, 178 culture-negative febrile cases, 28 “other” (i.e., non-Salmonella) pediatric infections, and 48 healthy Nigerian children. The best discrimination was achieved between TF and healthy children. LPS-specific IgA and IgM provided receiver operator characteristic areas under the curve (ROC AUC) values of 0.963 and 0.968, respectively, and 0.978 for IgA+M combined. Similar performance was achieved with t1477-specific IgA and IgM (0.968 and 0.968, respectively; 0.976 combined). IgG against LPS and t1477 was less accurate for discriminating these groups, possibly as a consequence of previous exposure, although ROC AUC values were still high (0.928 and 0.932, respectively). Importantly, discrimination between TF and children with other infections was maintained by LPS-specific IgA and IgM (AUC = 0.903 and 0.934, respectively; 0.938 combined), and slightly reduced for IgG (0.909), while t1477-specific IgG performed best (0.914). A similar pattern was seen when comparing TF with other infections from outside Nigeria. The t1477 may be recognized by cross-reactive antibodies from other acute infections, although a robust IgG response may provide some diagnostic utility in populations where incidence of other infections is low, such as in children. The data are consistent with IgA and IgM against S. Typhi LPS being specific markers of acute TF.

Redefining typhoid diagnosis: what would an improved test need to look like?

“…For example, a recent study has shown that IgA and IgM against S . Typhi lipopolysaccharide may be a specific marker of acute typhoid infection and is a promising target for diagnostic test development 25…”

Plasma Immunoglobulin A Responses Against 2SalmonellaTyphi Antigens Identify Patients With Typhoid Fever

“…We have previously identified HlyE in high-throughput immunoscreens as an antigen that correctly identified individuals with acute typhoid or paratyphoid fever in Dhaka, Bangladesh, using plasma and antibody-in-lymphocyte supernatant, a surrogate marker of the mucosal immune response, and this finding has been confirmed by other groups [28,29,33]. HlyE is a pore-forming toxin that affects bacterial growth within human macrophages and contributes to the cytotoxicity and invasion of epithelial cells [17][18][19].…”

“…In a study in which human challenge participants in the United Kingdom were used as a training cohort and typhoid cases and febrile controls from Nepal were used for validation, IgA responses to LPS had the highest diagnostic accuracy (AUC, 0.88) for a single antigen-antibody isotype, but HlyE was also selected for accuracy in several models [28]. In a study in Nigeria, LPS IgA, IgM and IgG responses (AUCs, 0.90-0.93) and HlyE IgG responses (AUC, 0.91) performed well in distinguishing typhoid from other infections [29]. In our current analysis in South Asia, we found that HlyE IgA (AUC 0.93) performed better than LPS IgA (AUC, 0.92) or MP IgA (AUC, 0.83).…”

Typhoid Fever Diagnosis in Endemic Countries: A Clog in the Wheel of Progress?

“…The candidates for the ELISAs in the Nigerian setting was based on a proteome microarray data previously carried out by the same research group where they identified hemolysin E and LPS as putative biomarker targets. The receiver operator characteristic area under the curve (ROC-AUC) values suggested that LPS-specific IgA and IgA+M ELISA, in particular, was sensitive in diagnosing acute typhoid, and could discriminate well between typhoid and healthy, and other febrile bacteremias commonly encountered in Nigeria [ 62 , 63 ]. In another study in Bangladesh, 12 proteins were expressed and purified to design ELISAs and tested in a cohort of febrile patients.…”