Application of ddPCR for diagnosis and treatment monitoring of visceral leishmaniasis patients: addition of an ultrasensitive tool to the diagnostic arsenal

Since the available tools in the arsenal toward accurate diagnosis and treatment monitoring of visceral leishmaniasis (VL) are limited. Therefore, efforts are still ongoing to develop an ultrasensitive molecular diagnostic tool applicable for endemic settings. In this evaluation study, we report on the efficiency of a digital droplet PCR (ddPCR) assay for diagnosis and treatment monitoring of VL. A total of 60 blood samples from VL patients were collected before the administration of antileishmanial drug. Upon treatment, blood samples were collected from each patient at 30 days and 180 days post-treatment. Blood samples from an equal number of healthy control subjects were collected from the same endemic region. Both qPCR and ddPCR were performed with the DNA extracted from blood samples to detect and quantify Leishmania DNA. Both of the molecular methods exhibited high sensitivity in diagnosing VL patients. Moreover, leishmania DNA was detected 180 days post-treatment in three VL cases that were diagnosed as VL relapse. The ddPCR showed an excellent analytical sensitivity in detecting as few as 0.1 Leishmania donovani parasite genome equivalents/reaction. With this promising quantitative ability, the ddPCR method showed a high positive correlation (r = 0.8) with the qPCR assay in determining the parasite loads in the clinical samples. Along with the commendable sensitivity, ddPCR showed absolute specificity as well. The findings of the study substantiate the excellent performance of ddPCR for diagnosing and treatment monitoring of VL patients. However, further multicenter studies are a prerequisite to evaluate the applicability of this tool in the endemic settings. IMPORTANCE This is the very first study to report the use of digital droplet PCR (ddPCR) for diagnosis and treatment monitoring of visceral leishmaniasis patients. By leveraging this ultrasensitive tool, absolute quantification of the parasite in the clinical samples is possible without requiring standard DNA materials. Eventually, this method will be useful for monitoring the relapse of visceral leishmaniasis (VL) patients and the post-kala-azar dermal leishmaniasis patients as well, who have been playing a critical role in transmitting the disease at the post-elimination period of VL. Moreover, the successful establishment of this method will pave the way for the detection and quantification of the parasite in asymptomatic carriers and sand fly vectors, which will strengthen the post-elimination surveillance of visceral leishmaniasis in the endemic settings.