Clinicopathological progression and molecular characterization of intestinal dilatation syndrome in commercial brown layers

Intestinal dilatation syndrome (IDS) is a poorly described condition affecting layers and breeder hens globally. Its prevalence is increasing, particularly in free-range systems, but the cause remains unknown. This retrospective study examined 35 hens from 3 flocks: free-range flock A (n = 20) and enriched-caged flock B (n = 5), both affected by IDS, and enriched-caged flock C (n = 10), with no history of IDS. Clinicopathological studies were performed on these hens, and metagenomic analysis was conducted on the proventriculus and jejunum of hens from flock A (n = 2) and flock C (n = 2). Based on clinical signs and lesions, 3 progressive stages of IDS were identified. In the first stage, although hens were without clinical signs, proventricular dilatation and lymphoplasmacytic and heterophilic jejunitis and duodenitis were observed. The second stage was marked by cachexia, pale and small combs and wattles, and severe egg production drop. Jejunal dilatation was observed, with microscopic evidence of necrotic, lymphoplasmacytic and heterophilic jejunitis; ganglioneuritis; and mineralization of the jejunal nervous plexuses and subserosal ganglia. In the third stage, spontaneous death occurred due to jejunal volvulus and vascular involvement. Affected hens (stage 2) also exhibited elevated cloacal temperatures (>0.9°C) and marked heterophilia. Metagenomic analysis identified sequences consistent with Megrivirus C in IDS-affected hens and a disruption of the gut microbiota, with increased abundance of Fusobacterium mortiferum and Megamonas funiformis . In conclusion, this study describes in detail the clinicopathological progression of the IDS and suggests that Megrivirus C , in combination with opportunistic intestinal bacteria, could play a role in the pathogenesis of this disease.