Interaction of Mycoplasma hyopneumoniae, Porcine Circovirus type 2, and Porcine Reproductive and Respiratory Syndrome Virus

Abstract

Porcine Respiratory Disease Complex (PRDC) is the most serious concern for swine producers in Korea and other countries. The most common viral agents involved in PRDC include Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Classical Swine Fever (CSF), Swine Influenza Virus (SIV), Pseudorabies Virus (PRV), and Porcine Circovirus type 2 (PCV2). Bacterial Pathogens associated with PRDC include Mycoplasma hyopneumoniae, Pasteurella multocida, Bordetella bronchiseptica, and Haemophilus parasuis, Streptococcus suis and the Actinobacillus spp. It is important to know that the interactions between pathogens can be a major factor in determining severity of the disease. The successful control of PRDC is based on the accurate diagnosis of the problem pathogens present on a herd basis. And it has been found that timing of intervention strategies, whether antibiotics or vaccines, is increasingly important on a herd basis. The objective of this thesis is to determine the effects of those pathogens and vaccine efficacy throughout experimental model and challenge test.

Part I is with PCV2 and Mycoplasma hyopneumoniae vaccinations on disease severity in an experimental PCV2-M. hyopneumoniae dual challenge model. Vaccine effectiveness was evaluated using microbiological (PCV2 viremia and M. hyopneumoniae nasal shedding), immunological (neutralizing antibodies and IFN-γ-secreting cells), and pathological (gross lung lesions, histopathologic pulmonary and lymphoid lesions, and the presence of PCV2 antigen and M. hyopneumoniae DNA within the lesions) evaluations. Although M. hyopneumoniae potentiates the severity of PCV2-associated lesions and lesion-associated PCV2 antigen level in dually challenged pigs, vaccination against M. hyopneumoniae alone did not reduce PCV2 viremia, PCV2-induced lesions, or PCV2 antigen in dually challenged pigs. In addition, vaccination against PCV2 did not reduce the nasal shedding of M. hyopneumoniae, the M. hyopneumoniae-induced pulmonary lesions or the lesion-associated M. hyopneumoniae DNA in dually challenged pigs. Dual challenge with PCV2 and M. hyopneumoniae did not interfere with the induction of active immunity induced by a previous single vaccination for either PCV2 or M. hyopneumoniae. The results of this study demonstrated that (i) vaccination against M. hyopneumoniae alone did not decrease the potentiation of PCV2-induced lesions by M. hyopneumoniae and (ii) vaccination against PCV2 alone decreased the potentiation of PCV2-induced lesions by M. hyopneumoniae in dually challenged pigs.

Part II is to determine the effects of Mycoplasma hyopneumoniae and/or PRRSV vaccination on dually infected pigs. In total, 72 pigs were randomly divided into nine groups (eight pigs per group), as follows: five vaccinated and challenged groups, three non-vaccinated and challenged groups, and a negative control group. Single-dose vaccination against M. hyopneumoniae alone decreased the levels of PRRSV viremia and PRRSV-induced pulmonary lesions, whereas single-dose vaccination against PRRSV alone did not decrease nasal shedding of M. hyopneumoniae and mycoplasma-induced pulmonary lesions in the dually infected pigs. M. hyopneumoniae challenge impaired the protective cell-mediated immunity induced by the PRRSV vaccine, whereas PRRSV challenge did not impair the protective cell-mediated immunity induced by the M. hyopneumoniae vaccine. The present study provides swine practitioners and producers with efficient vaccination regimes

vaccination against M. hyopneumoniae is the first step in protecting pigs against co-infection with M. hyopneumoniae and PRRSV.