PARTNER FEATURE ▶▶▶


Figure 3 - The effects of M. hyo on the replication of PCV2 in PK-15 cells.


6 4 2


PCV2 + M. hyo PCV2


0 24 Source: Wang, 2016. 36 48 Hours post PCV2 inoculation (h) 60 72


M. hyo also potentiated differently the severity of consequent PCV2 infection depending on PCV2 genotype. Dual infection with two pathogens produced more severe respiratory scores (highest for M. hyo + PCV2d), and reduced weight gain in pigs compared with pigs only inoculated with PCV2. The overall levels of PCV2d viraemia and severity of lymphoid lesions were significantly higher in pigs dually inoculated with M. hyo/PCV2d when compared with all other dually inoculated groups. The results of that study demonstrated that M. hyo potentiated the replication of PCV2d more than it did with the other PCV2 genotypes. Those results indicated that syner- gistic effects occur during the process of M. hyo and PCV2 sequential infection in experiments and also in the field condition. Vaccination against M. hyo significantly protected pigs against multiple viral infections, suggesting that vaccination against M. hyo decreases the risk of PRDC and reduces susceptibility of pigs to other viral pathogens.


M. hyo seems to provide an important site for PCV2 replica- tion in the lung. M. hyo was proven to enhance the replication of PCV2 in a time- and dose-dependent manner. Furthermore, different magnitudes of PCV2-infected cells were detected when co-in- fected with different M. hyo strains (see Figure 3 and Table 2).


In vivo study of PCV2 and M. hyo In an in vivo study, pigs inoculated firstly with M. hyo and two weeks later with PCV2 had increased PCV2-associated lesion severity. That increased severity was attributed to the ability of M. hyo to up-regulate macrophage proliferation and, there- fore, to facilitate PCV2 replication, together with an alteration of cytokine production.


Table 1 – Odds ratio (OR) for a positive pneumo- nia for a pig in different settings (farm type and vaccination status), based on the significant esti- mated coefficients of the cumulative link mixed model.


Setting A


Reference B


Reference B


Reference B


Reference C


Reference Farm type


Farrow-to finish Farrow-to finish Fattening Fattening Fattening


Farrow-to finish Fattening


Farrow-to finish Fattening


Farrow-to finish


PCV2 = Porcine Circovirus, type 2 Source: Raith, 2014.


12 ▶ PIG PROGRESS | Volume 38, No. 4, 2022


Vaccination status (PCV2) Vaccinated


Non-vaccinated Vaccinated


Non-vaccinated Vaccinated


Non-vaccinated Vaccinated Vaccinated


Non-vaccinated Non-vaccinated


OR 0.95 0.78 0.51 0.53 0.65


Conclusion The above-mentioned results of the extensive research demon- strated the pivotal role of both M. hyo and PCV2 in the develop- ment of PRDC. They act directly by causing different types of pneumonia and indirectly by affecting the defence mecha- nisms, facilitating other viral or bacterial infections. Efficient control of those infections is essential to protect the integrity of lung tissue and maintain functionality of the local immune sys- tem so that it can combat other co-infections. Respiratory health can then be monitored in slaughter pigs via lung lesion scoring. At the same time, other infections that may aggravate the course of respiratory disease – such as PRRSv, swine influenza virus or P. multocida – must be watched care- fully. That way differential diagnosis can be done properly, oth- er infections can be controlled and disturbance can be avoided through PCV2 and M. hyo post-vaccine immunity.


References available upon request.


Table 2 – Effects of different M. hyo strains on the replication of PCV2 in PK-15 cells.


M. hyo strains NJ


WX


XLW-1 168 TH AH


PCV2-infected cells (%)* 351 ± 28 157 ± 16 150 ± 14 167 ± 17 341 ± 18 162 ± 16


* The percentages of PCV2-infected PK-15 cells with different M. hyo strains were expressed relative to the number of PCV2-infected cells among untreated PK-15 cells. Source: Wang, 2016.


The titre of PCV2 (Log10


TCID50


/ml)


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44