Development and Assessment of Loop-Mediated Isothermal Amplification (LAMP) Assay for the Diagnosis of Human Visceral Leishmaniasis in Iran

Background

Parasitological methods for the diagnosis of Visceral leishmaniasis (VL) require invasive procedures, so serological and molecular approaches have been developed but are not generally applicable in the field. We evaluated a loop mediated isothermal amplification (LAMP) assay using blood from VL patients and compared it to nested PCR.

Methods

Forty-seven subjects with clinical features (fever, hepatosplenomegaly and anemia) were confirmed positive for VL by the direct agglutination test (DAT) at titers >3200. Forty DAT negative individuals from non-endemic areas with no clinical signs or symptoms of VL served as controls. A LAMP assay was performed using a set of six primers targeting Leishmania infantum kinetoplast DNA (kDNA) minicircle gene under isothermal (64 °C) conditions. For nested PCR we used primers targeting the kDNA minicircle gene.

Results

The LAMP assay provided a detection limit of 1 parasite in 1 ml of peripheral blood and detected L. infantum DNA in 44 of 47 DAT-confirmed VL cases, with diagnostic sensitivity of 93.6% (95% CI). No L. infantum DNA was amplified in controls, indicating a specificity of 100%. The nested PCR yielded sensitivity of 96% (95% CI) and a specificity of 100% (95% CI).

Conclusion

The LAMP assay gave results similar to those of nested PCR but in a shorter time. The LAMP method is simple; requires no sophisticated equipment; has a short reaction time; and results, indicated by turbidity of the reaction mixture, are observable with the naked eye.