Abstract
A swine influenza virus (H1N1) was isolated for the first time in Ontario from pigs one week to one and one-half years old during an epizootic which occurred between January and May 1981. Each herd outbreak was characterized by the sudden onset of marked respiratory distress, usually affecting the entire herd, accompanied by paroxysmal coughing, anorexia, prostration and temperatures as high as 41.5°C and lasting for five to seven days. Morbidity was nearly 100%; mortality was less than 1%.
Hematology, bacteriology and postmortem studies were conducted on 18 pigs from 11 farms. A lymphopenia and acute hematological inflammatory cellular responses characterized by neutrophilia with a left shift, hyperfibrinogenemia and a decreased plasma protein: fibrinogen ratio were found in 50% of the pigs. The cranial lobes of the lung were collapsed and red due to a bilateral cranioventral pneumonia which affected the cranial, middle, accessory and cranioventral aspects of the caudal lobes. Histologically, there was a necrotizing bronchitis and bronchiolitis with a neutrophilic cellular exudate. Pasteurella multocida was the species of bacterium most frequently isolated from the lung; however, mixed cultures of P. multocida frequently combined with Corynebacterium pyogenes and other species were usually identified in the lung and other organs of pigs submitted dead.
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