Otitis in a weaned pig: a new pathological role for Actinobacillus (Haemophilus) pleuropneumoniae

A weaned pig exhibiting clinical signs characteristic of a vestibular syndrome (abnormal head tilt and abnormal gait including a tendency to circle) was examined as a representative example of a condition which, in a 12-month period, affected approximately 400 other pigs on the farm of origin. The condition caused significant morbidity and financial loss but the directly attributable mortality was negligible. Post mortem examination revealed a severe suppurative, left-sided otitis media and interna. Mixed growths of bacteria, including Actinobacillus pleuropneumoniae, were isolated from the pus from the middle ear. Otitis caused by mixed bacterial infections has been described previously in pigs and cattle but infection of the porcine middle ear cavity by A pleuropneumoniae is considered to be a new pathological role for this organism. Other findings in this case indicated that otitis media had followed from bacterial colonisation of the auditory (Eustachian) tube. The condition was effectively controlled by prophylactic antibiotic therapy. The authors consider that vestibular syndrome due to otitis media and interna, whether caused by infection with A pleuropneumoniae or not, is probably a relatively common condition in England but its significance may be underestimated and for this reason it may be underrecorded.