Loss of leishmanin skin test antigen sensitivity and potency in a longitudinal study of visceral leishmaniasis in Bangladesh

Annual leishmanin skin test (LST) surveys were conducted in a visceral leishmaniasis-endemic Bangladeshi community from 2002 through 2004, using Leishmania infantum antigen from the same manufacturer and batch. In 2002, 530 (35%) of 1,532 had positive LST results; the prevalence increased with increasing age. The LST result was positive in 24 (51%) of 47, 18 (72%) of 25, and 11 (85%) of 13 kala-azar patients treated in the previous 1-11, 12-23, and 24-35 months. A positive LST result in 2002 was associated with protection against subsequent kala-azar (P < 0.0001). In 2003-2004, decreased antigen sensitivity was observed. Among 686 participants, 34% were LST-positive in 2002, 29% in 2003, and 19% in 2004. Of 63 cured kala-azar patients, 70% were positive in 2002, 53% in 2003, and only 30% in 2004. Among 171 participants tested with both antigens, L. infantum study antigen sensitivity was 70% compared with L. amazonensis antigen. Our data underscore the need for better production, standardization, and documentation of sensitivity, potency, and stability of leishmanin antigens.