Multiplex qPCR assay to determine Leishmania infantum load in Lutzomyia longipalpis sandfly samples

Case report: Diagnosis of visceral leishmaniasis using metagenomic next-generation sequencing and bone marrow smear

Visceral leishmaniasis (VL) is a chronic infectious disease transmitted by sandflies. The primary clinical manifestations are remittent fever, pancytopenia, and splenomegaly. As VL is rare with atypical symptoms, its diagnosis is often incorrect, missed, or delayed. Without appropriate treatment, the case fatality rate of symptomatic disease is more than 95%, but the prognosis is good if diagnosed and treated timeously. We report a case of VL that was diagnosed using metagenomic next-generation sequencing (mNGS) of a peripheral blood sample. By using mNGS and a bone marrow smear, we were able to make a timely diagnosis. The patient was treated with antimony, rapidly recovered, and was discharged from the hospital. This case illustrates the value of mNGS for making a timely diagnosis of VL.

Concurrent molecular characterization of sand flies and Leishmania parasites by amplicon-based next-generation sequencing

BACKGROUND

Phlebotomine sand flies are vectors of Leishmania parasites, which are the causative agents of leishmaniasis. Herein, we developed an amplicon-based next-generation sequencing (Amp-NGS) to characterize sand flies and Leishmania parasites simultaneously targeting partial fragments of 18S rDNA and ITS1 genes, respectively.

METHODS

Our assay was optimized using reference sand fly (n = 8) and Leishmania spp. (n = 9) samples and validated using wild-caught sand flies from Palestine. The assay was highly specific, and all DNA references were successfully identified to the species level.

RESULTS

Among the wild-caught sand flies (n = 187), Phlebotomus spp. represented 95% of the collected samples (177/187), including Ph. sergenti (147/187, 79%), Ph. papatasi (19/187, 10.2%), Ph. perfiliewi (3/187, 1.6%), Ph. tobbi (2/187, 1.2%) and Ph. syriacus (6/187, 3.2%). Sergentomyia spp. represented only 5% (10/187) of the collected samples and included S. dentata (n = 6), S. fallax (n = 2), S. schwetzi (n = 1) and S. ghesquiere (n = 1). The study observed strong positive correlation between sand fly identification results of the Amp-NGS and morphological identification method (r = 0.84, df = 185, P < 0.001). Some discrepancies between the two methods in the identification of closely related species (i.e. Ph. perfiliewi, Ph. tobbi and Ph. syriacus) were observed. Leishmania DNA was detected and identified as L. tropica in 14 samples (14/187, 7.5%).

CONCLUSIONS

Our assay was sensitive to detect (limit of detection was 0.0016 ng/reaction) and identify Leishmania DNA in sand flies, thus representing a new tool for studying sand flies and their associated Leishmania parasites in endemic areas.