Transmissible viral proventriculitis (TVP) is a disease of chickens, mostly broilers, of 2 - 8 weeks of age. Chicken proventricular necrosis virus (CPNV), a birnavirus, is the etiological agent. Characteristic gross lesions are enlargement, atony and pallor of the proventriculus. Four hundred seventy seven cases diagnosed in California between 2000 and 2018 were analyzed. They originated from 93 different farms representing all major companies in the region. Frequency of cases varied widely between the years. There was no recognizable seasonality. The flocks were between 6 and 61 days; the average age was 34.0 days and the median age was 35 days. In 166 cases, between 6.3% and 100% of the submitted birds had gross lesions in the proventriculus. Most common findings were enlarged or dilated proventriculi, thickened walls and pale or mottled serosal appearance. Histopathologically, inflammation of the glands was the most frequent finding. Other lesions included necrosis and/or hyperplasia of the glandular epithelium, dilated glands and occasionally fibrin deposition, fibrosis and hemorrhages. Twenty-three proventriculi from six cases were tested by immunohistochemistry for the presence of CPNV antigen; 21 stained positive. In 209 cases, birds also had lesions in the bursa Fabricii attributed to infectious bursal disease, but there was no significant difference in the mean percentage of birds with gross lesions in the proventriculus between cases with or without lesions in the bursa Fabricii. The results show that TVP is a common disease of broiler flocks in California and confirms that CPNV as the likely causative agent.

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