Septicemia associated with Actinobacillus suis infection in growing pigs in Korea

Actinobacillus (A) suis is a small, gram-negative rod and an opportunistic pathogen that colonizes the upper respiratory tract in pigs.

Outbreaks of disease occur in high health status herds or new herds. Infected pigs may have lesions related to septicemia and/or respiratory disease, such as hemorrhagic and necrotic pneumonia. Although acute septicemia with death occurs mainly in suckling and recently weaned pigs, it can be observed in growing, finishing, and adult pigs. Here, we report a case of A. suis septicemia in growing pigs in a Korean domestic herd.

The case involved pigs that were 80 to 100 days old located on a two-site farm in July of 2015. Approximately 5% of growers died, and dead animals did not show any previous clinical signs. The pigs in this farm were negative for PRRS. Two dead pigs were necropsied and various organs were fixed in 10% buffered formalin. The fixed samples were embedded in paraffin and stained with H&E and Gram stains. Diagnostic confirmation was made based on the detection of pathogens by polymerase chain reaction (PCR) and bacterial culture from the lung. PCR was used to detect PRRSV, PCV2, Pasteurella multocida, Streptococcus suis, Haemophilus (H) parasuis, A. pleuropneumoniae, and A. suis.

Grossly, the thoracic cavities in all pigs contained a large amount of dark brown fluid. The cranioventral lung lobes showed a dark red discoloration and a firm to rubbery consistency with fibrinous adhesions to the thoracic wall. Microscopically, the lungs showed severe fibrinonecrotic pleuropneumonia with bacterial colonies within the alveoli. Multiple foci of coagulation necrosis with bacterial colonies were observed both in the liver and spleen.

Intralesional bacterial colonies showed gram-negative coccobacilli with a Gram stain. All pigs demonstrated positive results for A. suis and H. parasuis with PCR. In addition, NAD-independent A. suis was cultured from all lung samples. All of the isolates were sensitive to amoxicillin, ampicillin, cefazolin, colistin, enrofloxacin, florfenicol, ceftiofur, tiamulin, and sulfamethoxazole/trimethoprim.

Based on the gross, microscopic and microbiological features, these cases were diagnosed as A. suis infection in growing pigs. The gross features of the lung lesions may be confused with pleuropneumonia caused by A. pleuropneumoniae in growing and finishing pigs. Therefore, a diagnosis of A. suis should be confirmed by PCR or bacterial culture from affected pigs. To the best of our knowledge, this is the first report of A. suis infection in growing pigs in Korea.

Disclosure of Interest: None Declared.