Long-term follow-up of Mycoplasma hyopneumoniae-specific immunity in vaccinated pigs.

Mycoplasma hyopneumoniae is the primary agent of enzootic pneumonia in pigs. To minimize the economic losses caused by this disease, M. hyopneumoniae vaccination is commonly practiced. However, the persistence of M. hyopneumoniae vaccine-induced immunity, especially the cell-mediated immunity, till the moment of slaughter has not been investigated yet. Therefore, on two commercial farms, 25 pigs (n = 50) received a commercial bacterin intramuscularly at 16 days of age. Each month, the presence of M. hyopneumoniae-specific serum antibodies was analyzed and the proliferation of and TNF-α, IFN-γ and IL-17A production by different T cell subsets in blood was assessed using recall assays. Natural infection with M. hyopneumoniae was assumed in both farms. However, the studied pigs remained M. hyopneumoniae negative for almost the entire trial. Seroconversion was not observed after vaccination and all pigs became seronegative at two months of age. The kinetics of the T cell subset frequencies was similar on both farms. Mycoplasma hyopneumoniae-specific cytokine-producing CD4+CD8+ T cells were found in blood of pigs from both farms at one month of age but decreased significantly with increasing age. On the other hand, T cell proliferation after in vitro M. hyopneumoniae stimulation was observed until the end of the fattening period. Furthermore, differences in humoral and cell-mediated immune responses after M. hyopneumoniae vaccination were not seen between pigs with and without maternally derived antibodies. This study documents the long-term M. hyopneumoniae vaccine-induced immune responses in fattening pigs under field conditions. Further research is warranted to investigate the influence of a natural infection on these responses.

Influence of parity and reproductive stage on the prevalence of Mycoplasma hyopneumoniae in breeding animals in belgian farrow-to-finish pig herds.

BACKGROUND: Dam-to-piglet transmission plays an important role in the epidemiology of enzootic pneumonia on farms. Although Mycoplasma hyopneumoniae (M. hyopneumoniae) infections in breeding animals are often subclinical, their control could have a positive effect on M. hyopneumoniae infection levels in fattening pigs. This study investigated the presence of M. hyopneumoniae in the breeding population of ten Belgian farrow-to-finish farms suspected by the herd veterinarian to be M. hyopneumoniae infected. Gilt vaccination against M. hyopneumoniae prior to first insemination was practiced on nine of the ten farms. At four different time points in the reproductive cycle 20 animals were sampled on each farm, namely 30-40 days of gestation, 75-85 days of gestation, 3-5 days after farrowing, and 1-3 days after weaning. In total, tracheobronchial swabs and blood samples were collected from 344 gilts and 456 sows (n = 80/farm). Swabs were analysed for the presence of M. hyopneumoniae DNA using nested PCR and M. hyopneumoniae-specific antibodies were detected in serum with a commercial ELISA. Generalized linear mixed models with farm as random factor were used to test the effect of time point in the reproductive cycle and parity on M. hyopneumoniae PCR prevalence and seroprevalence. RESULTS: M. hyopneumoniae PCR prevalence ranged between 0% and 43.8% at the farm level and the seroprevalence between 32.5% and 93.8%. Gilts were significantly more M. hyopneumoniae PCR positive than sows at the 2-4th parity (P = 0.02) and > 4th parity (P = 0.02). At 30-40 days of gestation, significantly more breeding animals were PCR positive as compared to 75-85 days of gestation (P = 0.04), 3-5 days after farrowing (P = 0.02) and 1-3 days after weaning (P = 0.02). Gilts had significantly more often M. hyopneumoniae-specific antibodies than sows (P = 0.03). CONCLUSIONS: M. hyopneumoniae PCR prevalence varied a lot between farms and due to gilt vaccination the number of animals with M. hyopneumoniae-specific antibodies was high on most farms. Gilts were more often M. hyopneumoniae PCR positive than sows and positive animals were mostly found at 30-40 days of gestation. This emphasizes the importance of a sufficiently long quarantine period and proper gilt acclimation practices before introducing gilts to the sow herd.

Transfer of Mycoplasma hyopneumoniae-specific cell mediated immunity to neonatal piglets.

Mycoplasma hyopneumoniae is the primary agent of enzootic pneumonia in pigs. Although cell mediated immunity (CMI) may play a role in protection against M. hyopneumoniae, its transfer from sows to their offspring is poorly characterized. Therefore, maternally-derived CMI was studied in piglets from vaccinated and non-vaccinated sows. The potential influence of cross-fostering before colostrum ingestion on the transfer of CMI from dam to piglets was also investigated. Six M. hyopneumoniae vaccinated sows from an endemically infected herd and 47 of their piglets, of which 24 piglets were cross-fostered, were included, as well as three non-vaccinated control sows from an M. hyopneumoniae-free herd and 24 of their piglets. Vaccinated sows received a commercial bacterin intramuscularly at 6 and 3 weeks prior to farrowing. The TNF-α, IFN-γ and IL-17A production by different T-cell subsets in blood of sows, colostrum and blood of piglets was assessed using a recall assay. In blood of sows cytokine producing T-cells were increased upon M. hyopneumoniae vaccination. Similarly, M. hyopneumoniae-specific T-cells were detected in blood of 2-day-old piglets born from these vaccinated sows. In contrast, no M. hyopneumoniae-specific cytokine producing T-cells were found in blood of piglets from control sows. No difference was found in M. hyopneumoniae-specific CMI between cross-fostered and non-cross-fostered piglets. In conclusion, different M. hyopneumoniae-specific T-cell subsets are transferred from the sow to the offspring. Further studies are required to investigate the role of these transferred cells on immune responses in piglets and their potential protective effect against M. hyopneumoniae infections.

Effects of pre-farrowing sow vaccination against Mycoplasma hyopneumoniae on offspring colonisation and lung lesions.

This study investigated Mycoplasma hyopneumoniae colonisation and lung lesions at slaughter in pigs from vaccinated (V) and non-vaccinated (NV) sows, in two herds (A and B). In each herd, two sow batches were V against M. hyopneumoniae with a commercial bacterin at six and three weeks before farrowing and two sow batches remained NV. From each sow batch, laryngeal swabs were collected from the litters of five primiparous sows at weaning and seven days post-weaning. All samples were tested for M. hyopneumoniae by nested PCR. In total, 488 piglets were sampled. At slaughter, the extent of Mycoplasma-like pneumonia lesions (lung lesion score (LLS)) was assessed. The colonisation rates with M. hyopneumoniae at weaning and seven days post-weaning were (V-A=14.2, NV-A=20.0 (P=0.225); V-B=0.9, NV-B=0.8 (P=0.948)) and (V-A=0.8, NV-A=7.0 (P=0.039); V-B=1.8, NV-B=2.5 (P=0.738)), respectively. The average LLS (in per cent) was V-A=15.5, NV-A=26.4 (P=0.021); V-B=9.7, NV-B=8.4 (P=0.541). In conclusion, in herd A, with a substantially higher level of piglet colonisation at weaning than herd B, offspring from V sows had a significantly lower colonisation rate seven days post-weaning and a significantly lower LLS at slaughter compared with the offspring of the NV sows. This implies that sow vaccination might be useful for control of M. hyopneumoniae infections, although significant results may not be achieved at all times (such as in herd B).