Pneumonia and upper respiratory tract infections, such as atrophic rhinitis, are common and insidious diseases of swine. They are often considered causes of decreased rate of weight gain, inefficient feed conversion, and increased time to market, although these parameters do not absolutely correlate with the severity of lesions. Pasteurella multocida is associated with lower and upper respiratory infections, based on results of lung cultures at necropsy and cultures from swabs of the nasal cavity. In the lung, one study showed that nontoxigenic strains were most commonly isolated from acute to subacute pneumonic areas, and toxigenic strains were most commonly isolated from granulomas. In atrophic rhinitis, toxigenic strains are associated with severe, progressive turbinate atrophy. Experimentally, purified toxin induces turbinate atrophy when aerosolized into the nasal cavity or injected into the subcutis, muscle, or peritoneum.