Clinical presentation of enteric fever include . These symptoms overlap with malaria and other febrile illness which makes the prognosis presumptive and dependent on the serum testing.
The diagnostics used to detect enteric fever are mostly serological testing, globally. Serological testing has been more widely used than nucleic acid testing due to the simplicity and cost in the resources needed for testing while compared to NAT which require laboratory facility. The Widal test being the most popular method . Blood samples most popularly used for diagnosis and stool samples are recommended to be avoided due to asymptomatic faecal shedding following the infection. There are commercially available rapid serological tests like Typhidot (Malaysian Bioduagnostic Research Sdn Bhdd, KL, Malaysia) that detects the antibody against the S.typhi outer-membrane protein, Tubex TF (IDL Biotech, Sollentuna, Sweden) detects antibody against LPS an.-
NAT tests that are developed are mostly conventional PCR and LAMP have been demonstrated to have specificity of . the Merieux foundation is validated a NAT in Bangladesh and currently in progress in Democratic Republic of the Congo, Burkina Faso, Malawi and Ghana.
Serological testing globally has been shown to have poor sensitivity and inadequate specificity. WIDAL test has been also demonstrated to be an due to (a) cross-reactivity with antibody from many other infections (b) establishing a baseline in the population where the infection is endemic and actively vaccinated (A and L, 2000). A recent stakeholders engagement summarized that the current challenges in diagnostics needs to improve the sensitivity of the tests to >90% and specificity >95% (Richard et al., 2019)
Add WHO guidelines
AMR
Use Minette’s review
Path forward with multiplexing
CRISPR Scissors for molecular detection
With the pressing need for a NAT for enteric fever, WHO the ASSURED (Affordable Specific Sensitive User-friendly Rapid Equipment-friendly Delivered) characteristic diagnostics for low-resource settings \citep{S2016} . CRISPR-Cas based molecular detection are gaining popularity due to some of their ASSURED attributes like high sensitivity and specificity. Additionally, these methods rely on iso-thermal amplification of the target which results in rapid results and with limited dependency on simple equipment that could be battery powered for field deployment. However, to employ these methods for diagnosis of enteric fever, the ? needs to be further optimized to achieve affordability. With a focus on local manufacturing of the enzymes and assembly of a detector in Cameroon, we demonstrate that CRISPR-Cas detection could be made affordable and deliverable to the end user.
CRISPR-Cas based bacterial adaptive immunity depends on RNA to direct the Cas endonuclease to detect and destroy the foreign nucleic acid. Since the first demonstration of the ability of Cas13a to cleave non-targeted RNA after recognizing and cleaving the targeted RNA template \cite{East_Seletsky_2016}, CRISPR-Cas platform like Cas12-DETECTR \cite{Chen_2018}, Cas14-DETECTR , Cas13-SHERLOCK are finding wide application in molecular diagnosis. While Cas13a recognizes RNA as a template strand, Cas14 recognizes ssDNA and Cas12 recognizes ds/ss DNA. The choice of any these molecular scissors depends on the needs of the end product. CRISPR-Cas technique has now widely applied to detect human papillomavirus \cite{Chen_2018}, ZIKA virus \cite{Kellner_2019}, DENGUE and also the 2020 pandemic Sars-CoV-2 \cite{Broughton_2020,Ding_2020}.