Severe Histiolymphocytic and Heterophilic Bronchopneumonia as a Reaction to In Ovo Fowlpox Vaccination in Broiler Chicks

Abstract

Broiler chickens on several farms from a single poultry company experienced neurological signs and mortality in chicks between 3 days and 10 days of age over a 3-week period after use of a fowlpox-vectored infectious laryngotracheitis virus vaccine in ovo. At necropsy the lungs contained numerous tan or gray, opaque to translucent, 0.5-to 2.0-mm nodules in the parenchyma. Microscopic lesions were a multifocal severe lymphohistiocytic and heterophilic bronchopneumonia. Immunohistochemistry was positive for fowlpox virus in macrophages and lymphocytes, and polymerase chain reaction on paraffin-embedded lung tissues was positive for a fowlpox vector virus commonly used as a vaccine. The cause of the neurological signs was not determined. Keywords chickens, in ovo vaccination, fowlpox infectious laryngotracheitis vaccine, lungSeveral farms in a commercial broiler company experienced elevated mortality and neurological clinical signs of tremors, recumbency, torticollis, and wry necks in chicks ranging from 3 days to 10 days of age over a 3-week period in the spring of 2008. No management changes had been instituted at the farm level. Affected farms had a change in vaccination at the hatchery. Chicks on these farms received in ovo a vectored vaccine that contains fowlpox virus (FPV) with infectious laryngotracheitis virus gene inserts. Ages of vaccination ranged from 17.5 to 19.0 days of embryonation. The company veterinarian noted that flocks vaccinated at 17.5 to 18.0 days were more severely affected than those vaccinated at 18.5 or 19.0 days of embryonation. Gross lesions noted in the field included multiple tan to gray, opaque to translucent, 0.5-to 2.0-mm nodules within the lung parenchyma. Samples collected on the farms included formalin-fixed tissues (brains and lungs) and swabs for bacteriology of the brains. Additional farms submitted dead chicks, formalin-fixed and fresh tissue, or live chicks to the Poultry Diagnostic and Research Center laboratory at the University of Georgia for additional testing, including virus isolation and mycology culture. A total of 6 submissions for different farms were analyzed.Brain swabs were negative for bacteria, and virus isolation was negative for avian encephalomyelitis virus in the brains. Lung cultures were negative for bacteria and fungi. Brains and lungs were routinely processed, embedded, and sectioned at 4 mm with routine hematoxylin and eosin (HE) staining. All submissions (cases Nos. 1-6) had similar changes in the lungs. Microscopic changes in the lungs included multiple areas of numerous histiocytes and lymphocytes centered on the parabronchi. The inflammatory cells filled the airways of several parabronchi and extended from secondary bronchi (Figs. 1, 2). There were occasional areas of acute necrosis of the inflammatory cells with mild numbers of heterophils migrating through the histiocytes to the foci of necrotic debris. Approximately one half of the lung parenchyma was affected in several sections. Gomori methenamine-silver staining was negative for f...

Chicken cGAS Senses Fowlpox Virus Infection and Regulates Macrophage Effector Functions

“…Although well defined in mammalian systems, the function of chicken cGAS and STING has only more recently been identified ( 26 , 27 ). FWPV is an avian poxvirus that causes skin lesions and respiratory infections and can infect multiple cell types including macrophages ( 28 ). Here we show that the cGAS/STING pathway in chicken macrophages can sense FWPV infection and is responsible for the IFN-I response as well as for upregulation of BLB1.…”

Chicken cGAS senses fowlpox virus infection and regulates macrophage effector functions

“…Although well defined in mammalian systems, the function of chicken cGAS and STING has only more recently been identified (Gao et al, 2018;Vitak et al, 2016). FWPV is an avian poxvirus that causes skin lesions and respiratory infections and can infect multiple cell types including macrophages (Williams et al, 2010). Here we show that the cGAS/STING pathway in chicken macrophages can sense FWPV infection and is responsible for the IFN-I response as well as for upregulation of BLB1.…”