First report of the giant kidney worm Dioctophyme renale in a domestic dog from Costa Rica.

Dioctophyme renale, the giant kidney worm, is a parasitic nematode of domestic and wild carnivores, occasionally infecting humans. While widely reported in South America, it has not been documented in Central America before. A 3-year-old French bulldog presented with leukocytosis, thrombocytopenia, azotemia, pyrexia, vomiting, and apathy. Abdominal ultrasound revealed tubular structures in the right kidney, and urine sediment contained nematode eggs. Euthanasia was performed after severe health complications, and a necropsy was done. The right kidney revealed severe hydronephrosis with parenchymal atrophy, fibrosis, and lymphoplasmacytic/eosinophilic nephritis. A 25 cm long worm was morphologically and molecularly analyzed, showing morphometric characteristics compatible with D. renale. Mitochondrial cox1 and ribosomal 18S and ITS1 sequences derived from the specimen were highly similar (>98 %) to D. renale. Phylogenetic analysis of cox1 data clustered Costa Rican and Argentinian sequences irrespective of host and haplotype network revealed five geographically distributed haplotypes, with one shared between Argentina and Costa Rica. This study provides the first evidence of D. renale in Costa Rica, indicating local transmission risk. Considering the parasite's complex life cycle involving aquatic intermediate and paratenic hosts and the presence of susceptible wild carnivores in our country, environmental exposure represents a key risk factor. The findings highlight the need for a One Health approach integrating veterinary, public health, and environmental strategies to improve detection, prevention, and awareness of dioctophymosis in Central America.