Development and evaluation of fluorescent recombinase polymerase amplification (RPA)-based method for rapid detection of Necator americanus.

Background: Necator americanus is the predominant species causing hookworm infections in humans. Despite advancements in prevention strategies, mild cases of infection still occur, highlighting the need for improved detection technology. Recombinase Polymerase Amplification (RPA) is an isothermal molecular diagnostic known for its sensitivity, speed, portability, and widespread application in detecting various pathogens. Although several molecular assays are available for N. americanus, they have limitations in detecting mild N. americanus infections.

Methods: Fluorescent RPA primers and probes targeting the N. americanus internal transcribed spacer 2 (ITS2) gene were developed. The method's detection limit was assessed via serial dilution of genomic DNA. Specificity was confirmed against Clonorchis sinensis, Schistosoma japonicum, Fasciola hepatica, Ascaris lumbricoides, Enterobius vermicularis and Ancylostoma duodenale. Thirty samples identified as positive by Kato-Katz, along with 11 samples identified as negative by the method, were tested to evaluate the sensitivity and specificity of fluorescent RPA. Additionally, 287 field samples were tested for validation with these methods. All positive samples were identified as either N. americanus or A. duodenale.

Results: This study successfully developed a fluorescent RPA assay targeting the ITS2 gene of N. americanus. The length of the amplified fragment was 237 bp. Optimized conditions were achieved, resulting in a minimum detection limit of 1fg/µL, with no cross-reactivity with other pathogens. In laboratory validation, the fluorescent RPA assay demonstrated 100% sensitivity (30/30) and 100% specificity (11/11) compared to the Kato-Katz, and 100% sensitivity (29/29) and 91.7% specificity (11/12) when compared to the semi-nested PCR. In field validation using human fecal samples, the fluorescent RPA assay showed a sensitivity of 90.0% (36/40) and a specificity of 91.1% (225/247) compared to the Kato-Katz. And the sensitivity of the fluorescent RPA method compared to the semi-nested PCR method was 100% (34/34), while the specificity was 90.5% (229/252).

Conclusions: The fluorescent RPA assay presents a rapid and dependable method for detecting N. americanus in fecal samples. Its high sensitivity and specificity provide significant utility for field surveillance and early identification of N. americanus infections. This advancement could facilitate the rapid molecular diagnosis of N. americanus disease in hookworm-endemic regions.