In March 2019, the California Animal Health and Food Safety Laboratory (CAHFS)- Turlock branch received two submissions of broiler chickens from commercial flocks reporting increased mortality. Submissions consisted of either white or brown broilers. Submitted chickens appeared depressed with ruffled feathers. At necropsy, moderate to severely enlarged and pale kidneys were observed, with gross lesions indicative of dehydration. Microscopically, renal tubules were degenerated and distended with necrotic debris and tubular casts. The kidney parenchyma contained mononuclear inflammatory cell infiltrates and interstitial edema. Infectious bronchitis virus (IBV) was isolated and identified by RT-qPCR from kidney tissue pools and tracheal swab pools from both cases. Partial sequencing of the S1 hypervariable region was most similar to a local California variant, CA1737. The outbreak lasted roughly one week in both flocks, with 2% total mortality in the brown broilers and 20% total mortality in the white broilers. Final proof of the IBV strains causing a nephropathy will require fulfillment of Koch’s postulates. IBV associated with nephropathy has been sporadically reported in California chicken flocks and represents a significant pathogen due to its potential for inducing high flock mortality. The incidence of IBV associated with nephropathy diagnosis in chicken necropsy submissions to CAHFS system-wide from 1998-2019 is also reviewed.

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