Field validation of a Leishmania (Leishmania) mexicana exo-antigens ELISA for diagnosing tegumentary leishmaniasis in regions of Leishmania (Viannia) predominance

BACKGROUND: Several tests are performed to obtain better accuracy when diagnosing American tegumentary leishmaniasis (ATL). It is believed that antigens released via secretion, excretion and metabolism are more specific than are antigens released by the lysis of Leishmania parasites. Such antigens are known as exo-antigens (exo-Ag) and are formed from products released by cultured parasites in a way that is similar to that in which they cause infections in hosts. OBJECTIVE: We attempted to validate a Leishmania mexicana ELISA exo-Ag for ATL diagnosis in Midwestern Brazil. METHODS: A total of 281 patients were included in the study. We analysed pre-treatment blood from 98 ATL patients; out of those, 85.7% and 14.3% had cutaneous and mucosal forms, respectively. RESULTS: The exo-Ag accuracy was 83.99% (95% CI = 79.24–87.81) with a sensitivity value of 90.82% (95% CI = 83.46–95.09) and an overall specificity value of 80.33% (95% CI = 73.97–85.44). The positive predictive value and negative predictive value were 71.20% (95% CI = 62.72–78.41) and 94.23% (95% CI = 89.40–96.94), respectively. Among healthy controls, exo-Ag had a specificity of 91.25% (95% CI = 83.02–95.70); additionally, the test had specificity rates of 66.67% (95% CI = 46.71–82.03) in Chagas disease patients, 60.61% (95% CI = 43.68–75.32) in patients with rheumatic diseases, 76.92% (95% CI = 49.74–91.82) in pemphigus foliaceus patients, 87.50% (95% CI = 52.91–97.76) in leprosy patients, 87.50% (95% CI = 63.98–96.50) in VRDL-positive patients, and 77.78 (95% CI = 45.26–93.68) in deep mycosis patients. CONCLUSION: Based on the indicators of validity, we conclude that the results obtained in this study enable the recommendation of the exo-Ag ELISA for ATL diagnosis once it presented a reasonable accuracy compared to classical methods. Cost evaluations are necessary to completely define the role of this technique in large scale.