Miltefosine Resistant Field Isolate From Indian Kala-Azar Patient Shows Similar Phenotype in Experimental Infection.

Area of Science:

• Parasitology
• Immunology
• Drug Resistance

Background:

• Indian Kala-azar (KA) control is threatened by emerging drug resistance.
• Miltefosine (MIL), a key drug for antimonial-unresponsive cases, is also facing resistance.
• Limited understanding of the mechanisms behind MIL resistance in clinical isolates.

Purpose of the Study:

• To characterize a putative Miltefosine-Resistant (MIL-R) Indian Kala-azar clinical isolate.
• To investigate the molecular and phenotypic basis of MIL resistance.
• To correlate experimental findings with clinical observations in MIL-unresponsive patients.

Main Methods:

• Phenotypic drug sensitivity testing (EC50 determination) of clinical isolates.
• Gene expression analysis (LdMT, LdRos3) of MIL-Resistant (MIL-R) and MIL-Sensitive (MIL-S) isolates.
• In vivo studies using a hamster model to assess parasite load, liver weight changes, and immune responses (cytokines, ROS, NO, T-cell proliferation, mitochondrial potential).

Main Results:

• One clinical isolate exhibited significantly higher MIL EC50 (putative MIL-R).
• Downregulation of LdMT and LdRos3 genes was observed in the MIL-R isolate.
• The MIL-R isolate caused reduced liver weight reduction, retained parasite load, impaired T-cell proliferation, and suppressed cell-mediated immunity in hamsters.
• Phenotypic characteristics in the hamster model mirrored MIL-unresponsive patient profiles.

Conclusions:

• This study reports the first characterization of a MIL-R Indian Kala-azar isolate.
• MIL resistance is associated with specific gene downregulation and impaired host immune responses.
• The experimental model provides insights into MIL resistance mechanisms and clinical outcomes.