Pathohistological characterization of pigs from different herds with PRDC

Respiratory diseases provide major concerns regarding production efficiency, animal welfare, antibiotic treatment and consumer protection. Variable combinations of interacting etiological agents and management conditions are source of high complexity and led to the term of the Porcine Respiratory Disease Complex (PRDC). Clinical signs appear late in PRDC and even with cross-pathology and lung checks are not suited to detect all relevant components of the disease. Early detection and pathogen specific attribution of lesions is the classical field of histopathology. The aim of the present study was to give a detailed overview on occurrence and quantity of histological parameters in lungs of pigs with PRDC under field conditions.

58 German hybrid pigs (25-30 kg) were obtained from 29 herds with PRDC for routine diagnostics during herd health service. Pigs were clinically examined and dissected. Lung surface was subdivided into 76 triangles and alterations in each part were scored from 0 (no alteration) to 4 (the whole triangle involved). A detailed histological examination was made from 6 lobes of each lung (except intermediate lobe). Samples were taken from the visually most affected triangles. A score based on the complete range of reasonable histological parameters was developed to quantify degrees of the three main types of pneumonia for all lobes.

Interstitial pneumonia, bronchopneumonia and fibrinous/hemorrhagic pneumonia were detected in 70.3, 18.0 and 13.0% of the lung lobes, respectively, representing different grades, in pure ore mixed form. Macrophages and plasma cells in alveolar lumina, bronchi or bronchioli indicated the lowest degrees of pathological lung lesions. Highest degrees were associated with lymphocytes and macrophages infiltrating alveolar septa and the lamina propria of bronchi and bronchioles and with neutrophils in epithelia and lumina of bronchi and bronchioles. Infiltration of interlobular interstitia with lymphocytes and macrophages was preferentially found in lobes with high aberrations, followed by hyperplasia of the BALT.

Lungs from field cases with PRDC showed overlapping degrees of the three major types of pneumonia which could be scored individually, based on histopathological parameters. Distinct histological findings were suitable to define thresholds in degrees of individual pneumonia forms; they might be useful for diagnosis and prognosis in PRDC field cases. Comparing these pathohistological data with clinical and microbiological findings in a next step should generate a deeper insight into development of PRDC and the interaction and significance of pathogens involved.

Disclosure of Interest: None Declared.