Polymerase chain reaction-miniexon: a promising diagnostic method for mucocutaneous leishmaniasis

Mucocutaneous leishmaniasis is a chronic disease caused mainly by Leishmania species that belong to Viannia subgenus. It affects upper respiratory airways and may lead to deformity, dysphagia, and even death in severe cases. Diagnosis is a challenge because clinical and histopathologic changes are easily confused with other diseases, and conventional methods for parasite identification and culture have a low sensitivity. Molecular methods have been used in the last two decades. In 2007, we published a validation study using internal transcript spacers and kinetoplast DNA as molecular targets with satisfactory results. In this research, we tested miniexon gene as the target.

Mucosal tissue samples from 60 Colombian patients with clinical signs of mucocutaneous leishmaniasis were included. A composite reference standard defined 30 cases and 30 controls. Two blind observers performed patient classification and test application independently. Miniexon gene amplification generated: 226-230 bp fragment for subgenus Viannia; 308 bp fragment for L. amazonensis; 340 bp fragment for L. mexicana; and 418 bp fragment for L. infantum-chagasi.

Polymerase chain reaction (PCR) sensitivity for fresh samples was 87.5% (95% confidence interval [CI] 72.2-100), specificity, 95% (95% CI 83.0-100), and positive likelihood ratio was 17.5 (95% CI 2.58-118.93), similar to results obtained with paraffin-embedded samples. Agreement between observers was 96% (kappa = 0.912; 95% CI 0.815-1.000) for both subgenus Viannia and Leishmania.

We consider PCR-miniexon as a diagnostic method of first choice for mucocutaneous leishmaniasis due to its excellent diagnostic performance and its ability to discriminate between Leishmania and Viannia subgenera as well as between species belonging to Leishmania subgenus.