Leishmanin skin sensitivity in the inland delta of the Niger.

Leishmanin skin tests were applied to 266 subjects in the city of Mopti which is located on several islands in the center of the inland delta of the Niger in the Republic of Mali. The antigen employed contains 6-10 million killed leptomonads per ml in a sterile suspension preserved with 1:10,000 thiomersal and unlike the phenol suspended antigens, does not give false positive tests. Of the 249 subjects who completed the study 12 (4.8%) had positive reactions, the lowest positive reaction rate yet observed in Mali. No false positive reactions occurred among 139 subjects tested with a control solution of 1:10,000 thiomersal. The absence of known cases of cutaneous leishmaniasis in Mopti's permanent population and the absence of suitable vectors within the city would indicate that positive reactors reflect previous L. tropica infections acquired in the surrounding rural areas where the disease is known to exist or else previous infection with non-pathogenic mammalian or reptilian species of Leishmania.