Are We Now Well Prepared for Another Major Visceral Leishmaniasis Epidemic in Sudan?

Abstract

To minimize the chance for future visceral leishmaniasis (VL) epidemics such as the 1988-1991 epidemic in Sudan, several VL detection tools have been introduced. There are many VL diagnostics with excellent sensitivities, specificities, and ease of use reported. However, additional test characteristics should be considered for use in the detection of future VL epidemics. The potential for local production or uninterrupted availability, low production and application costs, and stability at ≥45°C are of the utmost importance. Of the antibody-, antigen-, or DNA-based methods introduced, only a liquid direct agglutination test (LQ-DAT) remains in routine use. The LQ-DAT test may be the ideal diagnostic for detection of VL epidemics due to its low cost ($0.50/patient), stability under frequent and long-duration electric failures, and high level of reproducibility. The improved reliability for VL detection achieved locally through incorporating autochthonous L. donovani strains in antigen processing and precluding toxicants in test execution provides optimal sensitivity and safety for routine and mass application.

Keywords: antibody; antigen; diagnosis; epidemic; visceral leishmaniasis.

Figure 1.

Three direct agglutination test (DAT) versions for the diagnosis of visceral leishmaniasis (VL). Two are currently in use, involving in execution the use of formaldehyde and β-mercaptoethanol (β-ME; C LQ-DAT) or β-ME only (C FD-DAT), and a third was recently developed (formaldehyde and β-ME-free; A LQ-DAT) and applied to 2 VL (+) and 2 non-VL (-) sera. All 4 sera were tested through 2-fold serial dilutions starting at 1:100, up to 1:6400. The test outcomes were similar for all 3 versions; they were read by locating a circumscribed blue spot (end point) in the titration row that resembles the 1 in the control well containing diluent only (extreme left column); the serum dilution that preceded the end point is considered the titer of the serum sample under investigation. Titers ≥ 1:3200 are indicative of VL. All 3 DAT versions showed comparable readings: positive titers of ≥1:6400 in the VL (+) and negative titers of ≤1:100 in the non-VL (-).