Abstract
Attaching and effacing Escherichia coli (AEEC) are increasingly recognized as causes of enteric and systemic disease in birds. However, large-scale outbreaks in psittacines are seldom reported. We describe a severe AEEC outbreak in a colony of 144 lorikeets (Trichoglossus spp.) in an indoor walk-through zoo enclosure in the Netherlands, which resulted in 75.7% mortality (109/144) and additional mortality in cohabiting species. Affected birds showed nonspecific signs, including lethargy, inappetence, recumbency, and death within 24 h. Necropsy revealed enteritis with intramural and hepatic abscesses, and histopathology confirmed multiorgan inflammation and septicaemia. E. coli was consistently isolated from intestinal and hepatic lesions; PCR and whole genome sequencing identified multiple co-occurring AEEC pathotypes. Nectar feed samples demonstrated contamination and rapid bacterial proliferation, implicating inappropriate feed as the most probable outbreak source. This event represents one of the few documented E. coli-associated mass mortality events in captive psittacines and the first to propose simultaneous circulation of distinct AEEC variants during a single outbreak. The findings highlight the pathogenic potential of AEEC in lorikeets and the need for strict feed hygiene, vector control, and molecular surveillance in zoo biosecurity and One Health contexts.