Western
Meeting of Poultry
Clinicians and Pathologists
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Clinicians and Pathologists
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An Unusual Infectious Bronchitis Variant in California Leghorn Chickens A.A. Bickford, C. Gustafson, G. Cooper and B. Charlton California Veterinary Diagnostic Laboratory System
In April 1996, two successive submissions of 15-week-old Hyline W77 pullets were received with a complaint of gasping and other respiratory signs in a small percentage of the 47,000 bird flock. A total of 20 pullets were examined at necropsy and 18 serum samples were tested. The major necropsy finding was mild to moderate excess of mucus in the tracheas of 18 pullets, and petechiation of the proximal tracheal mucosa was noted in one bird and blood-tinged mucus was present in the lower third of the tracheas of 8 birds. Serological test results were as follows: seropositive to MG-18; seronegative to MS-18; strongly seropositive to Newcastle (titers greater than 4096 by HI, mean titer 30,778 by ELISA), paramyxovirus 3 (titers up to 2048 by HI); strongly seropositive to infectious bronchitis (mean titer 14,000 by ELISA, variable titers by HI – up to 1:32 for ARK99, up to 1024 for MASS, up to 2048 for CONN); seronegative for avian influenza-18. Histopathologically, tracheal lesions were unique in that there was extensive proprial edema and occasional focal hemorrhages. In addition, there was extensive deciliation, attenuation or slight hyperplasia of epithelium and mild to moderate mixed inflammatory cell infiltration of the propria. A coronavirus (identified by direct electron microscopy) was readily isolated in embryonated chicken eggs, but was not typable with CVDLS techniques. The isolate could not be identified by monoclonal antibodies in the fluorescent antibody test on the CAM, but it was detected by dot blot using the IBV group monoclonal antibodies. Evaluation of the virus by reference infectious bronchitis virus laboratories have thus far indicated that it is a distinct type, but there is disagreement on identity. One laboratory identified the isolate as Delaware 072, but the other laboratory has not been able to confirm this. Efforts to establish serotype and PCR identity of the virus are continuing. Meantime the affected flock recovered quickly from the acute respiratory phase of the infection and are currently healthy and producing at the expected rates. We have recently determined that these birds were vaccinated with killed Newcastle-bronchitis vaccine at 12 weeks of age and this may, in some way, have accounted for some of the unique serological reactions noted at 15 weeks of age. Follow-up serology in June 1996 indicated that the HI titers for infectious bronchitis were very similar to those noted in April. |
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