Performance of rK39 immunochromatography and freeze-dried direct agglutination tests in the diagnosis of imported visceral leishmaniasis

Visceral leishmaniasis (VL) is one of the neglected tropical diseases that require a global policy for integrated control programs. The disease is fatal if untreated, affects ∼500,000 persons/year, and is most prevalent in poor countries. Treatment is expensive and carries a risk of toxicity. Therefore, sensitive and specific diagnosis of VL is crucial to avoid under- or overdiagnosis. Selecting an appropriate serological diagnostic test is an issue of controversy and depends on geographic location. The study aimed to evaluate the performance of two serological techniques: recombinant antigen K39 (rK39)-immunochromatographic (IC) lateral flow assay (InBios, USA) that uses a recombinant Leishmania antigen K39 and the specific IgG detection by direct agglutination test (DAT, for the diagnosis of imported VL in non-endemic region (Saudi Arabia). The diagnostic accuracy of the two assays was assessed using bone marrow aspiration, direct microscopic examination, and culture on NNN agar as the “gold standard”. The bone marrow specimens from Indian, Sudanese, and Bengali patients (n = 98) with suspected VL features were cultured. Thirty-five specimens were positive (36%). The sensitivity and specificity of rK39-IC test were 89% (95% CI 78–99) and 92% (95% CI 85–99), respectively. DAT (with cutoff ≥1:1,600) showed comparable results (sensitivity 94%; 95% CI 87–101 and specificity 95%; 95% CI 90–100). To conclude, the performance of rK39-IC test and DAT is comparable. Both tests are moderately sensitive and specific and could be used to facilitate the global drive to eliminate this disease. The rK39-IC test is a rapid, easy-to-perform test and can be used as a point-of-care diagnostic method.