Evaluation of Immunohistochemical and Microbiological Methods for the Diagnosis of Brown Trout Infected withHafnia alvei

In this work we describe pathological and microbiological methods to establish the diagnosis of the Hafnia alvei infection in fish. This pathogen was isolated from a population of brown trout Salmo trutta displaying abnormal swimming, swollen abdomens, and mortalities. Brown trout were experimentally inoculated with H. alvei isolates by intraperitoneal infection to evaluate the histopathology of the disease, and some of the challenged fish exhibited signs of hemorrhagic septicemia. Histological changes observed in the kidney included some necrotic areas, macrovacuolar degeneration in the liver, and loss of the lymphatic tissue in the spleen. Specific granular anti-H. alvei immunoperoxidase labeling was observed in the brush border of proximal segments of the tubular cells and in the base of the intestinal villi. Hafnia alvei was reisolated and identified from the kidney of all the naturally and experimentally infected fish. We conclude that this infection can be successfully detected in fish by microbiological and immunohistochemical methods.