The aim of the study was to assess the effect of simultaneous experimental inoculation of PCV2 (intranasal inoculation) and Mhyo (transtracheal inoculation) into conventional, seropositive six-week-old piglets. Under the conditions of the present study, concurrent inoculation of PCV2 and Mhyo into pigs seropositive for both pathogens did not result in potentiation of PCV2- and Mhyo-induced clinical signs and lesions. However, the concomitant inoculation of PCV2 was associated with a higher load of Mhyo in the bronchus, which is one of the major target sites for this infection.

Taking into account the fact that infection with both agents was confirmed by means of laboratory techniques, the present study suggests that the timing of inoculation, initial pig serological status and the nature of the inoculum used may determine the final outcome of the co-infection.

In previous experimental studies, co-infection with Mhyo and PCV2 resulted in a more severe clinical disease in growing and adult animals. These studies, involved naïve pigs inoculated firstly with Mhyo and two weeks later with PCV2.

Mhyo is the main aetiological agent of enzootic pneumonia (EP), a chronic respiratory disease that affects mainly growing and finishing pigs. The main clinical sign of EP is a gradual onset of a non-productive cough caused by bronchointerstitial pneumonia. Mhyo is also part of the aetiology of the porcine respiratory disease complex (PRDC), which involves bacterial as well as viral agents. One of these viral agents is PCV2, the essential causative agent of postweaning multisystemic wasting syndrome (PMWS), a multifactorial disease with a severe impact on pig production worldwide.

PMWS is characterised by wasting, decreased weight gain, enlarged lymph nodes and dyspnoea, affecting mainly late nursing and fattening pigs. Although infection with PCV2 can be sufficient to cause the full spectrum of PMWS lesions, co-infection with other viral (e.g. porcine reproductive and respiratory syndrome virus [PRRSV; porcine parvovirus [PPV;] and torque teno sus virus 1 [TTSuV1]) and bacterial (Mhyo) pathogens tends to exacerbate clinical disease and the PCV2-induced gross and microscopical lesions.

This work has been published in: Sibila M, Fort M, Nofrarías M, Pérez de Rozas A, Galindo-Cardiel I, Mateu E, Segalés J. Simultaneous porcine circovirus type 2 and Mycoplasma hyopneumoniae co-inoculation does not potentiate disease in conventional pigs. J Comp Pathol. 2012 Aug-Oct;147(2-3):285-95.

July 2013