Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/1996
Publication Date: N/A
Interpretive Summary: Avian influenza is a disease of poultry caused by a virus. When the virus infects chickens the outcome can vary from no disease to a respiratory disease to a severe deadly disease. International trade and national disease control programs require the U.S. government to distinguish the less severe forms from the deadly disease. However, the ability to distinguish between disease forms can be frustrating because of time and scientific limitations of the currently used laboratory tests. This study determined the benefits of using two procedures that used the microscope as aids in diagnosing avian influenza and classifying it as to the deadly or less severe disease forms. For the less severe form of the disease, the virus grew in the lung and trachea of chickens, and produced death of only specific cell types. However, the viruses that caused the deadly disease grew all over the body, especially in the brain, heart, pancreas, kidney and lung and killed a wide variety of cell types. These different patterns as determined by the microscope, can help veterinarians determine if avian influenza is making the chickens sick and whether the disease is the deadly form or a milder form.
Technical Abstract: Pathological changes and distribution of viral antigen were compared among chickens inoculated intratracheally (IT) with either one of three highly pathogenic (HP) or one of two mildly pathogenic (MP) avian influenza viruses (AIVs). Extremely variable clinical signs ranging from mild respiratory distress to high mortality were present. Chickens inoculated with HP virus had histological lesions of necrosis and inflammation, in decreasing order of severity, in thymus, cloacal bursa, spleen, heart, pancreas, kidney, brain, trachea, lung and skeletal muscle whereas chickens inoculated with MP virus had histological lesions typically only in lung and trachea. Immunospecific staining for AIV proteins were most common in heart, lung, kidney, brain, and pancreas of chickens inoculated with HP AIVs, but only present and infrequently in trachea and lung of chickens inoculated with MP AIVs. The pattern of organ involvement and viral antigen distribution for HP AIVs indicates a common capability to spread beyond the respiratory tract, and confirms the pantrophic replicative, pathobiologic and lethal nature of the viruses. By contrast, the MP viruses had the ability to replicate and produce lesions within the respiratory tract, but exhibited a restricted ability to replicate and/or produce lesions in a limited number of non-respiratory tissues and only in association with sporadic deaths.