[3] Actinobacillus pleuropneumoniae is a nonmotile, Gram-negative, encapsulated coccobacillus bacterium found in the family Pasteurellaceae.

[3] Actinobacillus pleuropneumoniae was found to be the causative agent for up to 20% of all bacterial pneumonia cases in swine.

The symptoms include respiratory distress, bloodstained discharge (usually frothy) from the mouth, fever, anorexia, mild diarrhea, cyanosis, lethargy, and spontaneous abortion in sows.

[4] Differences in virulence potential, immunogenicity, and worldwide geographical distribution contribute to the diversity of the A. pleuropneumoniae serotypes.

The bacterium rapidly colonizes the host and attaches to the epithelial cells of the tonsils, moving down to the respiratory tract using type IV fimbriae.

[4][10] As the bacteria replicate, they release cytotoxins (in the form of Apx toxins), hemolysins and the lipopolysaccharides (LPSs)on their outer membranes.

[4] The subsequent lysis of macrophages causes a release of lysozymes, which in turn cause the tissue damage seen in porcine pleuropneumonia.

[11] The typical presentation of A. pleuropneumoniae in pigs is the characteristic demarcated lesions in the middle, cranial, and caudal lobes of the lungs.

[12] Overcrowding in pigpens, co-infections of other respiratory pathogens, and unusual stress all contribute to the spread of the disease.

[13] Such losses usually result from medication and veterinary expenses, increased mortality of pigs, extra labor, and other factors, such as reduced weight gain.