Pleuropneumonia Caused by Actinobacillus Pleuropneumoniae Biotype 2 in Growing and Finishing Pigs

Actinobacillus pleuropneumoniae biotype 2 was isolated in pure culture or as the predominant isolate from the lungs of 9 growing and finishing pigs with pleuropneumonia. Gross and microscopic lesions resembled those caused by A. pleuropneumoniae biotype 1 serotypes (nos. 1, 5, and 7) traditionally seen in the United States. The overall mortality rate for growing and finishing pigs on this 1,200-sow far-row-to-finish farm ranged from 0.37% to 0.84% per month from July 1990 to February 1991, and mortality due to respiratory disease ranged from 0.17% to 0.52% per month for the same period. This Actinobacillus species did not require V factor (no satellitism on blood agar with a Staphylococcus streak), was strongly beta-hemolytic, and dem- onstrated restriction fragment length polymorphisms in hybridization studies with A. suis, A. lignieresii, and A. equuli. Biochemically, the isolate most closely resembled A. pleuropneumoniae, and a DNA fragment considered specific for A. pleuropneumoniae biotypes 1 and 2 was demonstrated using polymerase chain reaction. Necro- hemorrhagic pleuropneumonia similar to that caused by A. pleuropneumoniae biotype 1 was reproduced ex- perimentally in 2 4-week-old pigs inoculated intratracheally with broth cultures of the A. pleuropneumoniae biotype 2. This study demonstrated the presence of A. pleuropneumoniae biotype 2 in the United States. Actinobacillus pleuropneumoniae, sometimes in pleuropneumonia caused by A. pleuropneumoniae bi- conjunction with Pasteurella multocida, is the most otype 2 in a swine herd in the United States. This common cause of porcine pleuropneumonia. 8 Actino- isolate was used to experimentally reproduce the dis- bacillus pleuropneumoniae pleuropneumonia (APP) is ease. most common in 2-5-month-old pigs (especially 30- 50-kg pigs), with occasional septicemia in pigs 30 days of age or younger. 13,17 Typical cases of APP are asso- ciated with pulmonary necrosis, hemorrhage, and characteristic involvement of the caudodorsal aspect of the caudal lung lobe. 12-14,21 Characteristically, ne- crotic areas are surrounded by darkly stained bands of streaming, swirling alveolar leukocytes; similar cells often line subpleural lymphatics. 18 Fibrin is prominent in alveoli from 2 to 4 days postinfection. 12 Other Actinobacillus species causing disease in swine include A. suis and A. equuli. Actinobacillus suis, A. equuli, and unspeciated actinobacilli are most com- monly isolated from the organs of septicemic nursing