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Bulletin No. 26 - Fall 2006
BacterologyMycoplasma hyopneumoniae
BUDDLE JR, O'HARA AJ
Enzootic pneumonia of pigs. A diagnostic dilemma.
Australian Veterinary Journal, 2005, Volume 83, Nš3, 134-139
The case reported in this paper is rather unusual due to a long-lasting succession of disconcerting events regarding the diagnosis of enzootic pneumonia (EP) in an Australian multisite production system. In one herd of this production system, swine showed severe respiratory signs which were first attributed to a combination of mixed bacterial infection and environmental dust, the culture of Mycoplasma hyopneumoniae being negative. Usually, a diagnosis is considered consistent with EP with the detection of both gross and microscopic lesions typical of M. hyopneumoniae. In that case, no definitive diagnosis could be established due to the presence of equivocal microscopic lesions. Subsequently, the persistence of the outbreak and the detection of gross and microscopic lesions typical of M. hyopneumoniae led to reconsider the hypothesis of EP. However, serological tests were negative. Two years after the initial outbreak, gross lesions were detected in another herd of the production system with still inconsistent laboratory results. At that point, polymerase chain reaction (PCR) test, which is considered as an almost-infallible diagnostic technique, was performed. Once more, the obtained results were disconcerting and the proportion of positive results did not match with the epidemiological pattern of EP, leaving the practitioners in the impossibility of providing a definitive answer to the producer. This case raises important questions about the interpretation and the limitations of diagnostic tests. For a pig producer, the commercial relationships of the herd and its internal management (vaccination, animal flows) are at stake and depend on the EP-free status. It is thus necessary for a pig veterinarian practitioner to be able to provide reliable answers in terms of diagnosis.
