There is a clear medical need for an accurate diagnostic test for typhoid that can be performed at point of care. Two antigens (lipopolysaccharide [LPS] and hemolysin E [HlyE]) have recently been identified that can distinguish typhoid from other bacterial infections. Here, we present the results of a diagnostic accuracy study of the Dual Path Platform (DPP) Typhoid assay (Chembio) that detects IgA to both LPS and HlyE using blood culture as the reference standard. This was a retrospective, observational, laboratory study conducted at the Aga Khan University research laboratory, Pakistan, to evaluate the sensitivity and specificity of the DPP Typhoid assay, using archived frozen serum samples collected during a previous typhoid diagnostic accuracy study (NCT04801602). The sensitivity, specificity, and accuracy (area under the receptor operating characteristics curve [AUC]) were then assessed using the manufacturer's and Youden's optimal thresholds. In total, 385 samples were included in the analysis. Using the manufacturer's thresholds, the sensitivity, specificity, and AUC were 97.8% (95% confidence interval [CI] 94.6-99.2), 65.3% (95% CI 58.5-71.6), and 81.5% (95% CI 75.5-85.3), respectively. At Youden's optimal threshold, the overall sensitivity of the DPP Typhoid assay was 89.7% and the specificity was 82.2%. In latent class modeling compared with other nine rapid diagnostic tests evaluated from the same cohort sample, the DPP Typhoid assay demonstrated the highest balanced accuracy (89.2%). The DPP Typhoid assay demonstrated a high diagnostic accuracy for typhoid fever. However, further adjustment to new thresholds is recommended to enhance its performance capabilities. IMPORTANCE Currently available diagnostic tests for typhoid have several limitations, including low sensitivity and specificity. Dual Path Platform Typhoid assay is a multiplex rapid test that detects IgA antibodies to lipopolysaccharide and hemolysin E antigen. It is considered to have high sensitivity and specificity, and its results were found to be highly correlated with ELISA results. However, very few studies have been conducted to evaluate this test and limited information about the accuracy of this test is present. Hence, this study evaluated the new typhoid test.
Background:Mycobacterium bovis (M. bovis) is the causative agent of animal tuberculosis (TB) which poses a threat to many of South Africa's most iconic wildlife species, including leopards (Panthera pardus). Due to limited tests for wildlife, the development of accurate ante-mortem tests for TB diagnosis in African big cat populations is urgently required. The aim of this study was to evaluate currently available immunological assays for their ability to detect M. bovis infection in leopards.Methods:Leopard whole blood (n=19) was stimulated using the QuantiFERON Gold Plus In-Tube System (QFT) to evaluate cytokine gene expression and protein production, along with serological assays. The GeneXpert® MTB/RIF Ultra (GXU®) qPCR assay, mycobacterial culture, and speciation by genomic regions of difference PCR, was used to confirm M. bovis infection in leopards.Results:Mycobacterium bovis infection was confirmed in six leopards and individuals that were tuberculin skin test (TST) negative were used for comparison. The GXU® assay was positive using all available tissue homogenates (n=5) from M. bovis culture positive animals. Mycobacterium bovis culture-confirmed leopards had greater antigen-specific responses, in the QFT interferon gamma release assay, CXCL9 and CXCL10 gene expression assays, compared to TST-negative individuals. One M. bovis culture-confirmed leopard had detectable antibodies using the DPP® Vet TB assay.Conclusion:Preliminary results demonstrated that immunoassays and TST may be potential tools to identify M. bovis-infected leopards. The GXU® assay provided rapid direct detection of infected leopards. Further studies should aim to improve TB diagnosis in wild felids, which will facilitate disease surveillance and screening.
Serological assays detecting IgM antibodies in addition to IgG antibodies have a diagnostic advantage in finding early infections. Staphylococcal protein A (SpA), widely used as an antibody-detecting reagent in various immunoassays, is considered to have a high binding affinity mainly to IgG, although its interaction with other classes of immunoglobulins has also been documented. Using 28 samples from 22 HIV-1 seroconversion panels, the present study demonstrated detection of early IgM antibodies by SpA-based rapid point-of-care tests, including DPP HIV 1/2, DPP HIV-Syphilis, STAT-PAK HIV 1/2, and Sure Check HIV 1/2. Samples with predominant IgM antibodies were identified by in-house IgM assays and confirmed by pretreatment with 0.1 M 2-mercaptoethanol. Likewise, the detection of treponemal IgM antibodies was shown by DPP HIV-Syphilis assay in eight samples collected at early syphilis infection. Direct interaction between IgM and SpA immobilized in solid phase or in solution was demonstrated with purified human polyclonal IgM. A strong correlation was found between the antibody levels detected by SpA and anti-IgM reagent in the early seroconversion samples, thus supporting the evidence for IgM binding by SpA. These assays demonstrated the ability to detect IgM antibodies, which may increase test sensitivity in early infections due to a reduced serodiagnostic window. IMPORTANCE Sexually transmitted infections, including HIV and syphilis, remain a global public health concern. The main laboratory testing approach for HIV and syphilis relies on serological assays. Detection of the IgM class of antibodies may have a diagnostic advantage in finding early infections. The present study using well-characterized HIV-1 and syphilis samples has demonstrated that staphylococcal protein A employed for antibody detection in rapid point-of-care tests, including DPP HIV 1/2, DPP HIV-Syphilis, STAT-PAK HIV 1/2, and Sure Check HIV 1/2, can capture IgM antibodies in addition to IgG antibodies. The findings strongly suggest that the ability to detect IgM antibodies by these immunoassays may facilitate the identification of acute-stage HIV and syphilis infections.
Recent studies have suggested the potential of innovative serologic tests for accurate and rapid detection of bovine tuberculosis (bTB). Dual Path Platform (DPP) technology has been used to develop rapid animal-side antibody tests for Mycobacterium bovis infection in a range of livestock and wildlife host species. The present study evaluated diagnostic performance of DPP BovidTB IgM/IgG assay designed for differential detection of bovine IgM and IgG antibodies against two chimeric antigens, DID38 and TBf2, respectively, using 662 well-characterized serum samples from M. bovis-infected and bTB-free cattle collected in the United States, Great Britain, France, and South Africa. Test sensitivity and specificity ranged from 71% to 100% and from 95% to 100%, respectively, depending on the country, with overall accuracy of 83%. No significant risk of cross-reactivity with serum samples from cattle infected with most relevant species of mycobacteria other than M. bovis was found. The DPP BovidTB IgM/IgG assay may be suitable for use in multi-test algorithms to improve current strategies for bTB surveillance.
Wildlife tuberculosis is a major economic and conservation concern globally. Bovine tuberculosis (bTB), caused by Mycobacterium bovis ( M. bovis ), is the most common form of wildlife tuberculosis. In South Africa, to date, M. bovis infection has been detected in 24 mammalian wildlife species. The identification of M. bovis infection in wildlife species is essential to limit the spread and to control the disease in these populations, sympatric wildlife species and neighboring livestock. The detection of M. bovis -infected individuals is challenging as only severely diseased animals show clinical disease manifestations and diagnostic tools to identify infection are limited. The emergence of novel reagents and technologies to identify M. bovis infection in wildlife species are instrumental in improving the diagnosis and control of bTB. This review provides an update on the diagnostic tools to detect M. bovis infection in South African wildlife but may be a useful guide for other wildlife species.
