(i) The URT includes the conjunctiva and harderian /lacrymal gland, nasal turbinates, nasopharyx, tonsils and mandibular LN, trachea, sinuses. and

(ii) Bronchi and bronchioles, loss of ciliated cells and mucociliary blanket and exposure of the basement membrane for the lodgement of bacteria. There may be an production of proinflammatory cytokines (IL-1, TNF-alpha) with local ingress of neutrophils and fibrinous exudates and pyrexia. These block the bronchioles and thicken their walls.

(iii)Alveoli, thickening of alveolar walls, interstitial pneumonia, fluid production, secondary bacterial pneumonia.eg porcine respiratory and reproductive syndrome.