Identification of an area predominantly endemic for childhood and adolescent visceral leishmaniasis in central Sudan.

Although widely spread throughout Sudan, visceral leishmaniasis (VL) is predominantly endemic in the Gedaref, southern Blue-Nile, and Umrimta areas located in the eastern, southern, and central regions, respectively. Regardless of form (endemic or epidemic), VL occurrence follows similar patterns as all ages and both sexes are affected. From January 2005 to May 2016, we received a total of 563 patients with high suspicion for VL from various endemic areas; 159 were children and adolescents (0.5-18 years) from Umrimta (central Sudan). A significant observation during this 11-year period of uninterrupted monitoring using a standard liquid direct agglutination test (LQ-DAT) version was the exclusive VL occurrence (100%) in the child and adolescent populations of Umrimta when compared with other endemic areas (27.3%-48.0%). Among 12 child and adolescent suspects who initially tested marginal in the standard LQ-DAT, 6 scored unequivocally positive readings both in an improved LQ-DAT version (based on an autochthonous Leishmania donovani strain) and rK28 VL reference test. None of the 4 (2.5%) VL adult suspects (≥19years) referred had positive outcomes in the improved LQ-DAT version or the VL reference freeze-dried direct agglutination and rK28 tests. Further incorporation of antigens derived from autochthonous L. donovani strains from Umrimta (central Sudan) or Gedaref (eastern Sudan) in LQ-DAT significantly increased the agglutination titer levels in the respective VL homologous sera (p=0.0263 T=505 and p=0.2814T=219), suggesting possible antigenic variation within the predominant Sudanese L. donovani complex. Additional research is required to determine characteristics other than the serologically-based ones reported for the L. donovani strain involved.