Wooden tongue (actinobacillosis), a sporadic disease of cattle, is caused by Actinobacillus lignieresii. The most prominent signs are pyogranulomatous lesions that affect the tongue and cause the tongue to become fibrous, shrunken and immobile. However, the pyogranulomatous lesions can also be found in other soft tissues such as the lymph nodes.
This case study reports an unusual outbreak of cattle of several herds affected by actinobacillosis affecting skin and lymph nodes. Nine isolates of A. lignieresii were isolated from the lymph nodes and identified by molecular analysis. A PCR for A. pleuropneumoniae was performed to exclude this species, as both species are indistinguishable by 16S rDNA gene analysis. An enterobacterial repetitive insertion consensus sequence PCR was used for genotyping and the repeats-in-toxin (RTX) genes were analysed by sequencing.
Five isolates from one outbreak on one farm shared the same genotype, which was distinctly different from the other isolates collected from different farms. A total of four genotypes were observed. All isolates contained the apxICABD operon. However, difference in the size of the apxIA and apxID genes were observed. The sequence alignment revealed that two isolates had a deletion of around 697 bp at about 736 bp into the apxIA gene. There was also a deletion of around187 bp at the beginning of the apxID gene.
The deletion and the ERIC PCR patterns suggested that several outbreaks occurred involving different A. lignieresii genotypes. The study provided no evidence of a unique virulence type associated with the A. lignieresii isolates. In turn, this suggests that the outbreaks were possibly due to a range of contributing factors, including environmental factors.