DIAGNOSTIC INVESTIGATION OF AMERICAN ROBINS (TURDUS MIGRATORIUS) WITH FATAL ETHYLENE GLYCOL TOXICOSIS AND CONCURRENT PLASMODIUM SPP. INFECTION WITH RETROSPECTIVE REVIEW OF 44 YEARS OF DIAGNOSTIC DATA.

We describe a mortality event involving at least 44 adult American robins (Turdus migratorius) that were found dead on the morning of February 25, 2023 in a residential backyard in Natchitoches Parish, Louisiana. Five carcasses were submitted for diagnostic evaluation. All five robins were in good nutritional and feather condition with no external indicators of injury or illness. Grossly, kidneys were diffusely pale in all robins and 4/5 also had splenomegaly. Consistent histologic lesions included severe, multifocal to coalescing, renal tubular degeneration and necrosis with intraluminal, birefringent calcium oxalate crystals and calcified concretions. Toxicologic testing revealed a markedly elevated calcium concentration (10,000 parts per million) in a pooled kidney sample. Collectively, these findings support a diagnosis of ethylene glycol toxicosis. Ethylene glycol, an ingredient in antifreeze, is a hazardous toxicant in domestic and wild animals living in residential areas, although confirmed reports in songbirds are scarce. In the present case, the circumstances of ethylene glycol exposure are unknown but most likely anthropogenic in origin. Additionally, splenomegaly prompted molecular testing, which detected Plasmodium unalis in three robins and P. vaughani in one robin. Both Plasmodium spp. can infect a wide range of hosts, and although infections likely were subclinical, their detection raises awareness of their potential pathogenicity in wild birds. This mortality event underscores the need to recognize health risks posed by environmental contaminants and vector-borne pathogens to wildlife, and reinforces that wildlife, especially peridomestic species, can serve as sentinels for risks to domestic animal and human health.