Pediatric Measles and Visceral Leishmaniasis Co-infection: Diagnostic Challenges and Insights Into Pathophysiology.

Measles remains a major cause of childhood morbidity worldwide despite the availability of an effective vaccine. Beyond its acute clinical manifestations, measles induces profound but transient immune dysfunction, predisposing affected children to secondary and opportunistic infections. Visceral leishmaniasis (VL) is a systemic protozoal infection caused by Leishmania species and is characterized by prolonged fever, hepatosplenomegaly, pancytopenia, and high mortality if left untreated. The coexistence of severe measles and VL poses a significant diagnostic challenge because of their overlapping clinical and laboratory features. We report the case of a previously healthy three-year-old boy admitted to the pediatric intensive care unit with severe PCR-confirmed measles complicated by acute respiratory failure and hemodynamic instability requiring invasive mechanical ventilation and vasoactive support. Persistent fever, progressive hepatosplenomegaly, and cytopenias despite initial intensive management prompted further investigation, which demonstrated positive rK39 antigen testing and elevated anti-Leishmania antibody titers, establishing the diagnosis of VL. The patient was successfully treated with liposomal amphotericin B, vitamin A supplementation, IV immunoglobulin, and supportive intensive care, resulting in complete clinical recovery without sequelae. To the best of our knowledge, no pediatric case of measles-VL co-infection has been documented previously. This case highlights the diagnostic complexity of persistent systemic inflammation and cytopenias in children with severe measles and illustrates the importance of considering endemic opportunistic infections when the clinical course is atypical or prolonged. The favorable outcome emphasizes the value of early recognition, timely pathogen-directed therapy, and multidisciplinary management, while reinforcing the critical role of measles vaccination in preventing severe disease and its infectious complications.